My brother recently wrote a blog post on the Driving Progression, which is a Dunning-Kruger of performance driving. I thought it would be fun to the do the same thing for aerodynamics.
If you don’t know what the Dunning-Kruger effect is, it’s that people with very little knowledge have a lot of confidence. They’ll freely share the benefit of their inexperience with everyone. As they gain knowledge, they start to realize they don’t know anything, and lose confidence, eventually reaching a low point of “I don’t know shit.” After hitting rock bottom, an increase in knowledge steadily rebuilds confidence to the point that they master the topic.
The D-K effect is not about being stupid, it’s about not knowing any better. That’s certainly how I started my journey through aerodynamics, and it’s probably similar to how other people got started.
I’ve identified four general stages of the D-K effect, which I’m calling Fanboi, Learning, Experiments, and Optimization.
Fanboi – Buying aero parts for looks, drag reduction, or blind trust.
Learning – The apple of knowledge brings despair.
Experiments– Tools and experiments to expand knowledge.
Optimizations – Applying aerodynamic principles to any object with good results.
Fanboi
The first phase of aerodynamics is largely acquiring parts without understanding their specific use.
Appearance – Many people buy aero parts because they look cool. Most dealer options like a front lip, side skirts, or spoiler are early on the upward slope.
Drag reduction – People easily grasp the concept of drag reduction, and not knowing any better, it defines the next level of purchases or DIY projects.
Blind trust – At this point a person has bought a wing or spoiler and some other aero that has good results (I dropped 3 seconds with a wing!), and now they think more aero is better and buy it all, whether or not it’s designed well or would be useful on their car.
The peak of the “acquiring without understanding” phase is probably canards. People who buy them don’t know why they’d want to spin a vortex on the side of the car, and often don’t have underbody aero anyway.
You can ask a fanboi why they have this aero part, or how it works, and you’ll get a reply that has nothing to do with personal aero knowledge and everything to do with blind trust in the manufacturer. Businesses have a vested interest in parting you with your money, are they really the people you should trust on this matter?
Some people never get past the Fanboi phase, and good for them, ignorance is bliss. But some of them watch a video or read a book, or god forbid they find this website, and then they fall down a very deep hole into despair.
Learning
The next phase begins when a person does actual research into aerodynamics, and thus begins a slippery slope down Dunning-Kruger’s backside. Often YouTube is their first inkling that things don’t work exactly the way they’d hoped. For example, maybe they saw Kyle Forster’s video on how wings don’t work with convertibles. Or they watch Julian Edgar read yet another bedtime story from his book.
Some people might stumble onto my Occam’s Racer website, and if you’re a regular reader, you know I do a lot of debunking and peeking behind the curtain. Other notable stops on the way to the pit of despair include Competition Car Aerodynamics, by MacBeath and Race Car Aerodynamics, by Katz.
From there you might dig deeper into to the grandfather of texts, Hucho’s Aerodynamics of Road Vehicles, or hit the lowest point, SAE papers and peer-reviewed university studies. At this point aerodynamics, or should I say, fluid dynamics, is so full of numbers, equations, and nerd stuff that you feel you know shit-all of nothing.
Experiments
Further knowledge comes through experimentation. Just as you were once a fool to trust aerodynamics manufacturers, you’d be a fool to trust anything you read or see on YouTube. So this next phase is where you get hands-on, experimenting to see the result.
Personally I jumped right into Airfoil Tools, OptimumLap, and other free resources, then DIY’d my own projects. A more sensible approach, and one I took later, is to enroll in Kyle Forster’s (JKF Aero) online course on aerodynamics.
Most of us aren’t going to have the means to get into CFD, and so Kyle does that for you, performing the experiments you’d do, and doing a nose-to-tail breakdown of CFD. If you are serious about aero, there’s no better use of your time or money.
It’s worth noting that Kyle uses OptimumLap in his course, since it’s a great way to get instant validation on whether something works or doesn’t, and how it plays out on different race tracks. I was already using the program for years before taking Kyle’s course, and it being FREE, everyone who is serious about aero or validating any other modifications to their car should use it.
The final stop in the Experiments stage is oddly where I started: real-world testing. That could mean going to a wind tunnel, or in my case, hiring a professional to make Watkins Glen into our own personal wind tunnel. And with that hard data, one comes to certain realizations about aero, and it turns out that it’s not that difficult after all.
Optimizations
Once you reach this level of understanding, you realize it’s not about the parts, but by applying certain principles. You are either optimizing the car for a particular rule set, or in the absence or racing rules, to handling characteristics, efficiency, a particular race track, or other factors.
The principles go something like this:
Attached flow – You want to keep air attached along surfaces. A thicker and turbulent boundary layer is better than detached. Streamlined objects have rounded leading edges. Break cleanly at the trailing edge.
Change the directionof air – If you aren’t changing the direction of airflow, you aren’t doing dick. Most often you want to send air upwards, creating an opposing force: downforce. You don’t want to change direction too much or air detaches, causing drag and destroying downforce.
Maximize suction – Pressure is good, suction is better. Maximize suction and minimizing losses to the underside of splitters, underbody, and wings.
Manage tires – Tires are draggy disruptive to airflow, creating a jet of air as they contact the ground. Manage tire drag and squirt to mitigate losses.
Manipulate vortices – Vortices are usually thought of in terms of loss and wasted energy, but you can manipulate vortices to create air fences, delay flow separation, reduce energy on the face of the tire, etc. At the bleeding edge of performance, like F1, it seems like most of the effort is spent managing and manipulating vortices.
Conclusion
There is nothing wrong with being on the early, upward slope of the Dunning-Kruger graph. Choosing aero parts because you like the way they look, or because you support a particular manufacturer, or because they work and you don’t care why, is a happy place to be. This covers the 90% usecase.
In reflection, I can’t think of a compelling reason to get into early aerodynamic texts or plunge into SAE papers, they can be too much. Instead, leave that shit to me, I’ll translate it for the masses and make it fun to read (I won’t say “dumb it down” because y’all are smart or you wouldn’t be here).
But if you really want to get into aerodynamics because you’re developing something for the last 10% of performance, or because you need a competitive edge, then I’d start with the JKF aero course. You’ll definitely be making your own aero parts, because the aftermarket doesn’t support the kinds of things you’ll be doing, so plan on investing in tools and materials.
This is a worthy journey, but all-consuming, and requires sacrifices. Have fun with it.
Generally speaking, touring cars are limited by front downforce, and so optimizing your wing for more rear downforce isn’t super useful. Buy a decent wing and conventional mounts, set it at roof height and zero degrees, and experiment with wing angle to taste. You don’t need to overthink this. However, I do.
I know that by optimizing my rear wing, I can get the same amount of rear downforce while reducing drag, either via less wing angle or less wing area. Some of that can be done by choosing the correct airfoil and using a 3D shape, but it also comes down to how and where I mount the wing. Because I also know that by locating rear downforce further forward, I can get more total downforce with the same aero balance.
And that presents a lot of choices, because wings can be mounted from the bottom, top, or sides, and at different heights and set-back distances. What’s best?
Wing location
In an ideal world you’d laser scan your car and do CFD testing to find out the wing location where you get the performance you’re looking for. Usually this would be where the car (not the wing) makes the most downforce, but you might also be looking for the car’s ideal lift/drag ratio for a particular race track, or for an ideal front/rear aero balance.
Most of us aren’t going to laser scan our cars, nor do we have the hardware and software to run CFD. More to the point, racing rules often restrict where you can put a wing. For example, some SCCA classes limit wings to 8″ above the trunk deck. Grid Life Touring Cup rules state that the wing can’t extend 5″ past the rear bumper. Some rules limit the wing to being entirely in front of the rear bumper!
But let’s start with a no-rules situation, what’s the best location for a wing? As a general guideline, wings should be mounted at about roof height. This provides enough area underneath the wing for the low pressure region to form, helps extract air from underneath the car, and is a good compromise of aero balance and center of gravity.
Mounting a wing higher than that will get the wing into less turbulent air, and the wing may make more downforce in that location, however, the car may make less downforce. Huh? When you place a wing above roof height, it loses interaction with the body of the car, and the rear wake doesn’t kick up as high. The net result is the overall Cl of the car (downforce) is reduced, even if the Cl of the wing is itself better.
In addition, the higher you place a wing, the more it affects rear aero balance, because it has more leverage. So unless you’re making an over abundance of front downforce, it’s not a good idea to get more rear leverage. Placing the wing higher also raises the center of gravity, which will be detrimental to handling.
Conversely, mounting a wing lower than roof height reduces rear leverage and lowers the center of gravity. In addition, a lower height can also help extract more from a diffuser. The downside is that the wing will make less downforce because there’s more turbulence behind the canopy, and there’s less area under the wing for the low pressure region to form. Indeed, the low pressure region under the wing may run into the high pressure area on the trunk lid.
The shape and angle of air also change as you lower a wing. If you read my post on 3D wings, you’ll know that if you mount a wing at roof height, there’s about a 5-7degree difference in angle between the ends of the wings and the center of the wing. If you lower the wing, that angle can be 10 or even 15 degrees. Which means if you mount a 2D wing close to the trunk, the wing is going to stall either at the ends or in the middle of the wing.
All said, mounting a wing at roof height is a good baseline setting for the vertical axis. The next issue is where to mount the wing on the horizontal axis. A good rule of thumb is to overlap the wing onto the trunk by 1/4 chord. Meaning, if you have a 12” chord wing, there should be 3” of wing in front of the trunk lid and 9” behind it. This baseline setting provides the ideal amount of extraction under the wing, which kicks the rear wake upwards and pushes the car down.
If you’re constrained by racing rules that don’t allow you to get a wing that far rearward, you’ll have to run more wing angle for the same amount of downforce. You’ll get more drag as a result of that, but rules be rules.
The only reasons I can think of to place a rear wing further rearwards than 1/4 chord overlap have to do with practicality or aero balance:
If you need to be able to open the trunk and the wing is in the way of that, then you could place the wing further rearward. Although you could also mount it higher. Performance wise, I’m not sure which is better, but this is concessions for practicality anyway.
If you have so much front downforce that you need to balance that with more rear leverage, you could mount the wing further back. But personally, I’d just add more rear wing, not a longer lever.
If your car is a hatchback, you may not be able to get enough space under the wing for the low pressure zone to form. Again the options are higher or further rearward, and it would be hard to say which is better.
Aero balance
Twice now I’ve touched on aero balance, and so a few words on that won’t be out of place. Typically you set up a car with the same aero balance as its chassis balance. So on a Miata with equal 50/50 weight distribution front/rear, you’d put the same amount of downforce on the front and back. On a FWD car with 67% of the weight on the front wheels, you’d skew aero balance 2/3 to the front. And on a rear-engine Porsche 911 you’d put 2/3 on the rear.
That’s how an aerodynamics engineer would baseline the aero balance on a car, but that’s not how I like it. I want a car to oversteer in slow corners and understeer in fast corners. This isn’t difficult to do, you just remove rear mechanical grip (or add front grip), and use a big wing.
On most racetracks, the slow corners are maybe 40 mph and the fast ones are say 90 mph. If the car oversteers slightly in a 40 mph corner and understeers slightly in a 90 mph corner, then there’s a whole range of speeds in the middle where the car is perfectly balanced.
I’ll dive into the details of aerodynamic balance in another post, but the point here is that the type of wing mounts you chose will slightly affect the aero balance by providing more or less leverage on the rear of the car. Mount a wing further rearward or upward and it levers up the front of the car, adding understeer. Place the wing further forward, and the aero balance moves forward, creating less understeer (or more oversteer, depending on how you look at it).
With that see-saw effect of aero balance in mind, let’s take a look at some wing mounting solutions.
Wing mounts
Wings generate downforce along the entire surface, but the downforce is centered at about 25-30% of the chord distance from front of the wing. So when mounting a wing, center your supports around that location. Next you might be wondering what kind of mounting solution is best, conventional mounts, swan necks, or end-plate mounts?
Conventional upright mounts
Wing mounts cause turbulence. If you’re read my post or watched the video on Visualizing Airflow, you’ll know that there’s a lot of turbulence right around the wing mounts (mounts = pylons, stanchions, stands, uprights, or whatever you want to call them). Some of that is due to air wrapping around, which adds even more turbulence.
All of that turbulence is happening beneath the wing, which is where most of the downforce is made. So you can see this is the worst case scenario for downforce and drag. Still, conventional mounts are short, stiff, and simple. Like I wrote at the beginning of this article, it’s front downforce that is the main limiting factor in your aero package, so there’s nothing wrong with using conventional bottom mounts and moving onto more important projects.
Trunk mount may require supports underneath.
Conventional mounts can attach to the trunk lid, trunk gutter, or chassis. If the trunk lid is rigid enough, that’s the easiest spot, as the wing pivots easily out of the way. On Miatas, the trunk lid isn’t that well supported, so we typically mount wings in the trunk gutter. The frame around the trunk is very stiff, and with just a little cutting around the trunk lid, there’s no interference when opening it.
Chassis mounting is for cars that produce a metric shit ton of downforce and can’t trust any part of the trunk or rear surfaces to mount a wing. Chassis mounts are heavier, and unless you need them, I don’t see the point; they just make you look like a poseur.
Chassis mounts are for serious downforce. Everyone else can just put them on the trunk or in the trunk gutter.
Swan necks
Swan neck mounts move the mounting and adjustment hardware to the top of the wing. The pressure side of the wing doesn’t matter much, and so adding turbulence here is of less consequence, which leaves the underside undisturbed. In addition, because there’s turbulence around conventional bottom mounts, you get earlier flow separation at steep angles of attack. Meaning that a swan neck mount allows you to run more wing angle before stalling.
Another thing I like about a swan neck mount is the ability to add in some calibrated flex. Normally I think of wing mounts as being rigid, but if the wing mount can flex a little, it allows you to drop a couple degrees of wing angle at high speed.
This is effectively an active aero system, or call it passive aero, but it would theoretically give you some of the benefits of a DRS system. A swan neck mount allows you to do this easier than other types of mounts. However, it’s of less benefit than you’d think, and you can read about that in my post on Active Aero.
Voltex swan neck looking good on fake Miata.
The only real drawback of a swan neck mount is structural. It’s a bit more wear on the wing and wing stands, and so the wing must be stronger, and the mounts must be larger and heavier than conventional bottom mounts.
Reverse swan necks
One fault of conventional swan neck mounts is that the wing stands are still in front of the wing. Flat plates aren’t great aerodynamically, airflow along the plate begins to detach with more distance, and eventually separates entirely, creating a turbulent wake.
Reverse swan necks place the wing mounts behind the wing, removing all turbulence in front of the wing. This is an ideal mounting solution if you can find a good way to mount it. And therein lies the rub.
Let’s use a Miata as an example. We know that the wing should be mounted at roof height and overlap the trunk by about 1/4 chord. That puts the the trailing edge of a standard-sized wing about 7″ behind the trunk lid. The wing mounts need to be behind that, and so if they go in the trunk gutter as usual, that would make for a very large S-curved wing mount. Audi has done something similar mounted to the trunk lid, as you can see in the image below.
Reverse mounted swan neck.
Now there’s nothing intrinsically wrong with S-curved wing mounts except for the weight of the materials and less rigidity in the system. But an easier solution on a Miata would be to come straight down and mount the wing to the chassis at the bumper supports.
A reverse swan neck wing mounted like that would be bomber strong. The mounts would weigh a bit more, but the real penalty is where the downforce is applied, very far rearward. However, I could see this being ideal for a time attack car, where you have huge splitters and hammerhead extensions that make a ton of front aero, and you need as much aero as you can get.
End-plate mounts
An end-plate mounted wing integrates the wing stands and end plates into one piece. There’s no additional vertical supports, so there’s no drag or turbulence generated from the wing mounts themselves, just the end plates, as it were. When I think of iconic cars that had end-plate mounted wings, I always think of a Ferrari F40. The wing didn’t have a very large chord, but it was a perfect marriage of form and function.
Ferrari F40 with end-plate mounted wings.
There are compromises with every mounting solution, and end-plate mounted wings require a stronger (heavier) wing. Wings generate most of their downforce in the middle of the wing, and when supported only by the ends, you need a very strong, rigid wing.
Another drawback is that end-plate wings are limited to the width of the car. You can’t easily put a 78″ wing on a 62″ wide car and mount the wing via the end plates. Well I guess you could, but the end plates would be angled heavily outward, not vertical. Most end-plate mounted wings are vehicle specific (like the F40, NSX, etc.), and so these are typically OEM offerings, not aftermarket.
9 Lives Racing makes an end-plate mounted Street Wang for Miatas that has angled wing mounts so that they can use a larger 48″ wing instead of a 40″ wing, which is the size of the trunk opening. The Street Wang is mounted a bit too low and aft for pure performance, but it looks good, provides trunk access, and as the name implies, is more of a street application anyway.
9LR Street Wang provides access to the trunk and lower downforce for dual-duty Miatas.
Recap
Every wing mount is a compromise:
Conventional bottom mounts are the easiest, lightest, and strongest. They also make the most drag and least downforce. But like I wrote in the first paragraph, that rarely matters on touring cars.
Chassis mounts are the strongest, but also heavy and usually restrict access to the trunk.
Swan neck mounts have less drag and turbulence. The downsides are mostly structural, but could be turned into an advantage.
Reverse swan neck mounts have less turbulence than conventional swan necks, but might increase rear leverage due to mounting location.
End-plate mounts offer the best performance, but they limit wing span, and the wing itself must be very strong.
Wing mounting solutions for a Miata, and the location of downforce applied. It’s a sketch; nothing is to scale.
This year I’m teaming up with Chris White and Josh Herbert to offer data coaching at Watkins Glen International, for events organized by Niagara PCA. Other dates and tracks are TBD, get in touch with us if you’d like us to bring our data program to your event.
Data coaching is using GPS and car telemetry data to understand what the driver is doing in minute detail, and suggest ways to improve speed, consistency, and safety. Data coaching has benefits to students, coaches, and HPDE organizations.
For students, data coaching is an individualized, actionable improvement plan, using the best information possible. Every student has unique strengths and weaknesses, and data coaching pinpoints exactly what the student needs to work on.
To driving instructors, data coaching is a way to teach more than one student per day. As a right-seat instructor, I can only focus on one student at a time, but as a data coach, I can coach several people per day, and follow up with them afterwards.
For HPDE organizations, data coaching is an effective way to reinforce the curriculum. If you want to see if the student is releasing the brakes gradually, or following a prescribed racing line, or anything else you are teaching in class or on track, it’s as simple as looking at the data.
Data is not only useful as a coaching tool, but as a snapshot from a point in time. For example, if you suspect that your car is down on power compared to a previous date, you can look back at the data and see if your longitudinal acceleration has changed. Likewise, you might change parts on your car, and by comparing with previous points in time, you can quantify the differences each part makes.
Who is data coaching for?
Novice drivers don’t need data; they need to listen to their instructor. In rare cases a highly analytical student might learn primarily through seeing graphs and numbers, but for the 95% case, data is not a useful learning tool at the novice level.
Intermediate drivers absolutely need data coaching. Most HPDE organizations only have enough instructors for novice drivers, so there’s very little in-car instruction or coaching after the novice level. As a result, intermediate drivers often plateau for a long time using only the skills they learned as a novice.
Advanced drivers are in one of three camps: 1) those who understand that data is essential, 2) those who have never tried it, and 3) those who don’t want to know how bad they suck. For the first group, you might book a data coaching session with one of us as a second opinion, but you’re probably already on the right track. The second group is why we have this program! We’ll provide the hardware, software, and know-how to make you a better driver. If you’re in the third group, we have a new program to help break the ice: vMin coaching.
vMin coaching
The largest hurdle to data coaching isn’t the hardware, the software, or the ability to read the data. It’s “I don’t want to know how bad I suck.” I’m not being flippant, these are the exact words I hear all the time.
Listen, we all suck at driving. Every one of us has some corner we can’t get our head around or are afraid of. For me, it’s Turn 6 at Watkins Glen. I had a racing incident there with another car (my fault), and I still pussyfoot my way into and out of that corner. If I’m being completely honest, I also underdrive the bus stop and T11. “Hello, my name is Mario and I suck at driving.”
What’s also normal is that you have one or more corners you’re really good at. I have a lot of confidence in T7. You probably also have corners that you’re really good at, too. But is that a good corner, or do you just think so? And by the same measure, are the corners you suck at really that bad?
So you don’t want anyone to know how bad you suck, but you want to find out which corners you need to work on. You can do that by looking (privately) at your minimum corner speeds.
The importance of vMin
Pretty much everyone knows who Ross Bentley is, and I’d wager a good percentage of us have read Ultimate Speed Secrets. Aside from publishing books and teaching classes, Ross also had a subscription series called Speed Secrets Weekly, which was a weekly email of driving advice. On his 500th and final installment of Speed Secrets Weekly, Ross Bentley chose to save the best for last, and focus on what is arguably the most important aspect of performance driving: minimum corner speed.
Minimum corner speed, often abbreviated vMin, is the lowest speed you achieve in a corner. Why did Ross choose to write about vMin in his final SSW?
Min corner speed is one of the best measures of driver experience: Intermediate drivers throw away speed to optimize late braking; Advanced drivers hoard min speed like it’s gold.
Raising your min speed is often the easiest way to go faster.
Earlier I wrote that intermediate drivers need data coaching. The primary reason is because they place too much importance on late threshold braking. Brakes are not just for slowing the car – brakes are for adding front grip, changing weight balance, turning the car, and above all, setting the ideal minimum speed for each corner.
If your vMin is too low, you can’t make it up by driving harder: applying throttle early in the corner results in oversteer or understeer. If your vMin is too high, you’ll have to roll off the throttle mid corner, or be later to full throttle. If your vMin is just right, the car is easy to turn and your car corners effortlessly. So how do we find the minimum corner speed for each corner?
Estimating vMin in every corner
At Watkins Glen, you can estimate your vMin in every corner by looking at turns 7 and 8. The vMin in these corners are usually within 1 mph of each other, and you can use the greater of the two vMin values to determine your min speed in every other corner. For example, Turn 1 is typically 108% faster than Turns 7 and 8. Turn 10 is about 135% faster. It doesn’t matter if you’re on R-comps or all-season tires, it’s the same ratio.
To data coach yourself, I’ll give you a lookup table, and you’ll start by circling your vMin in each corner. Then read from left to right across from T7-8 and you’ll probably see that most corners are in the same row. However, some corners will be above that line – those are corners you can improve on. In the example below, this person could raise their vMin in the bus stop, T6, and T11.
You might have noticed that the table says “No Aero” at the top. Tire compound doesn’t change the ratio between the speeds in each corner, but downforce does. So I’ve created different lookup charts for cars with no aero, and varying levels of downforce.
You might be wondering how I got all this data. A lot of it comes from looking at professional drivers on YouTube. That’s right, you don’t need a fancy data gathering devices to log vMin. A phone app or video camera showing the MPH is enough to get the min speed. Of course I also backed this up with lots of Aim Solo data from veteran drivers. I put all this data into a spreadsheet and averaged the values and came up with the ratios for each corner. It was surprisingly consistent.
If you want to coach yourself on vMin I’ll be offering a classroom lecture once per day. I’ll explain the concept in more detail and hand out the the lookup tables and a cheat sheet of strategies (mostly coming from Ross Bentley) that will help raise your vMin. You can choose to share that with other people, or keep the data private.
By working on your min corner speed, you can see huge gains in terminal speed. It won’t surprise me when one of you tells me that a 1 mph increase in vMin gave you 3-5 MPH at the end of a straight. Once you see how important data is as a feedback mechanism, some of you may want to go deeper into one-on-one data coaching.
One-on-one data coaching
If you schedule a one-on-one data session with me, Chris, or Josh, this is how a typical data coaching day goes.
First we’ll give you an AIM Solo and mount it securely in your car so that you can reach the power button and see the display. We have suction cup mounts and rollbar mounts, or can use any 1″ RAM style mount that’s already in your car.
In the first session, just drive as you normally would. We need to make sure the unit is functioning 100% correctly, and get some baseline laps. We also want to make sure you can see the delta timer, if you choose to use that.
Delta timer
If you’ve never used a delta timer, you’re in for a treat. Any decent motorsports data logger (or phone-based lap timer) can be set for predictive or delta time.
In predictive mode, the main display shows the lap time that the Aim Solo thinks you’ll do if you continue at this pace. I don’t like this setting, because lap times are not something we need to focus on – there’s too much importance put on this metric, and it’s too granular to be useful.
I much prefer the delta timer mode, in which the display shows a + or – sign with the amount of seconds that is different from your best effort at that particular point on track. So, if you roll through T1 at Watkins sGlen and glance at the delta timer going up to the esses and see -00.55, you’ll know that whatever you did in T1 this time was a lot better than before. You can use the delta timer to try different lines and techniques and get immediate feedback on whether it was a good idea and execution… or not.
The delta timer is a distraction, so don’t look at it unless you have clear track around you and you’ve unwound the steering wheel. But once you’ve gotten the hang of looking at deltas, it can be difficult to drive without that feedback.
Race studio analysis
After a couple track sessions, bring the unit back so we can download and review the data. The first thing we’ll do is load your best lap into Race Studio and look at the speed trace. The shape of the speed trace shows where you brake and how hard, where you get on the gas, and how smooth you are.
Next we’ll load up some more laps to see how consistently you’re driving. Consistency isn’t necessarily the goal here, because it’s good to experiment with lines, braking points, etc. But if you’re repeatedly doing something good or bad, it’s worth noting.
Next we might look at all your laps and split them into sectors. Analyzing sector times is a great way to stitch together different laps. In a crowded run group, it can be difficult to get a clean lap, and by using sectors, we can estimate what your runs would look like, even on a crowded day.
There are a lot of other things we can look at during our 1:1 sessions. Most of it will depend on what we see in the data, which tells us what you need to work on.
Advanced data coaching
There’s a limited amount of coaching we can accomplish in one day, but once we have your data, we can do follow-up sessions afterwards.
Comparisons – Similar car and tires, different drivers. What can you learn from other people? What can you teach us?
Lat and Long G – Are you braking and cornering at the limit?
Friction circle – How well are you blending inputs?
Areas for improvement – Backing up the corner, compromise corners, racing line, etc.
One of the great things about data coaching is that it keeps you engaged between events. So instead of going home and not thinking about driving until your next event, you can make a plan for what you’ll do on your next DE. Using data feels like it shortens the time between events, and makes you faster in the interim.
Computer simulations
Another thing we can do with advanced data analysis is to create a computer model of your car and simulate your car on track in the virtual world. This allows us to change the tires, aero, weight, power, etc, and see what potential benefit this provides.
For example, I see a lot of people focusing on weight reduction. If you could remove 100 lbs of weight, what will that do? Well, I can tell you exactly (or rather the computer can tell you). And that goes for adding power, decreasing drag, increasing downforce, switching to softer tires, and many other variables.
Like advanced data coaching, this is a service we’d have to do in a follow-up session. But it all starts with getting the data.
Get signed up!
If you want data coaching at Watkins Glen, sign up for one of the Niagara PCA events. The vMin coaching is free, and the 1:1 data coaching is a modest $50.
I attended my first Grid Life event this weekend at Watkins Glen International. It was probably the best motorsports event I’ve ever attended. T.J. Lathrop has a blog called the RISING EDGE, and did a great job describing what’s different and better about about Grid Life, so go read that for the overview.
I can sum up my feelings about Grid Life with this: It’s what I’m doing in the future. Here are some additional random thoughts I had on the weekend.
HPDE coaching
Most of the festival events were held Friday on Saturday, with Sunday reserved mostly for HPDE. I pestered the Grid Life staff enough that they allowed me to be an HPDE instructor at this event, and it was a different experience. There’s no in-car instruction for novices. Yes, you read that correctly. Instead, the instructors are assigned three students (ish) and we coach them actively between sessions.
The coaches are assigned different areas on the track, and we keenly observe and report over radios what’s happening. We then get our flock together and go over the finer points.
And that probably works really well for some students. For some students who need someone in the car with them, this may not work out as well. But I will say that the novice group was very well behaved on track, and I don’t think this is any worse than any other kind of novice instruction, it’s just different.
I definitely talked more to my students than I normally would. The conversations starts well before the event, so we get to know our students and most importantly, make sure their cars are track-ready.
In fact one of my students came over to my race barn and I got to pre-tech his Miata. I also showed him some hardtops and wings I’ve built, because in this strange world of coincidences, Lucien is a reader of this blog, and is one of a few who have bought me a coffee! I’m going to do him one better and eat at his family restaurant, Le Garmin Cafe, when I go to Lime Rock later this year. Lucien, it was great to meet you, come back later and let’s aero your Miata!
Aero
I’ll admit it: I spent too much of the event admiring or criticizing other people’s aero. Mostly criticizing.
But let’s start with the admiration. There were three pro-level time attack cars in the Toyo tent, and they were doing things I’ve only thought about.
Splitter cross section is an airfoil shape.
Such as using a wing-like profile for the shape of the splitter. And also, instead of using splitter diffusers, kicking the entire rear edge of the diffuser.
No need for splitter diffusers, the entire rear edge kicks up.
There was a lot of other cool shit, but I didn’t take enough pictures, and some of that stuff should remain a secret anyway. Now I’ll get on with being critical about other people’s aero.
TCR wing
I’m like the kid who says the emperor has no clothes. I’m a nobody; I have nothing to lose by telling it like it is. So I’ll just say it: the TCR wing looks like a piece of shit.
After some research, I found that this is the BE 183-176 airfoil, which is designed specifically for motorsports. To my eye, it’s got way too much camber. Just looking at how much it kicks in the rear I’m like, how does air stay attached to the bottom?
My buddy Josh Herbert was looking at the underside and pointed out that the rain had left water stains that was just like flow-vis paint. And sure enough, we could see that the air was clearly separating at the rear third of the wing!
Aside from the amount of camber it has, it’s also very thick. Airfoils generally gain downforce with thickness, and at around 12% that trend reverses. The TCR wing is 18% thick (as related to the chord of the wing), and you can see that thickness especially when viewing the wing head on. One driver complained of excessive drag when mounting the wing higher than spec, and I can see why – it’s a fucking brick.
Given the number of really good wings out there, I wouldn’t buy a TCR wing unless I was racing TCR. Full stop.
Build one yourself.
But some people have no choice. The TCR wing is a homologated part; every TCR car must use it. One of the stipulations is that the wings must be mounted such that no part of the wing, and that includes the wing mounts and endplates, can be higher than the roof. This means the wing itself is underneath the roofline, and that doesn’t help a wing perform well, especially since most of the cars are hatchbacks.
But it got me to thinking: this could be the reason the TCR wing is shaped the way it is, because of how low it must be mounted (per the rules). As such, perhaps it behaves mostly as a spoiler, meaning the pressure side of the wing (the top) is doing the work?
Now this kind of makes sense for the underside as well. Because the only way air is going to stay attached to that kind of bottom curvature is if the air is being accelerated into it. This is what happens when you run a second element wing, the top element is at an extreme angle, and air stays attached via acceleration through a convergent gap. Perhaps by mounting the wing below the roofline, the roof is itself acting as the main element (bottom) wing in a makeshift dual-element wing setup?
Possibly. This is all conjecture, since I don’t have a TCR wing to play with. I’ll try and get one and test it just for the science of it. I have the coordinates and could make one, but apparently they aren’t that expensive, and are manufactured and distributed by Volkswagen. Leave it to the people that fucked our asses with diesel-gate to bugger a racing series with a wing that stinks of shit.
S2000 hardtop
The Honda S2000 is a popular car in both GLTC and Club TR. In the past I haven’t paid much attention to the not-Miata, but there were more of them than actual Miatas at Grid Life.
I believe that every S2000 I saw had a hard top. Some had a replica OEM hardtop, but most were Seibon or maybe Mugen, I can’t tell the difference.
Most S2Ks had a hardtop sorta like this.
I did put an angle meter on the rear window and found it was 30 degrees. This is something I’ve written about before, that the absolute worst angle for the rear window (the backlight angle) is 30 degrees. Drag, turbulence, and separation, oh my!
Obviously a fastback would be a lot better, but I didn’t see anyone doing this. On my Miata, my DIY fastback was 15% less drag, and also helped my wing make 30% more downforce. You’d think with the high-dollar builds and level of effort in these cars that someone would figure out a fastback. But no.
I need a S2000 in my garage for a couple weeks so I can fab one. Get in touch with me if you want one, it’s one of those “for science” projects I’d like to do one day.
GLTC Aero
Grid Life Touring Cup made some minor changes to the aero rules for 2023. Splitter length is the same 3″ as before, and they still don’t allow splitter diffusers, or winglets, scoops, ducts, etc. on the blade. Splitters are now measured from the innermost vertical part of the front fascia, which has made some of them even shorter.
With these limitations, splitters aren’t going to make a lot of downforce. There are obvious and less obvious ways to work around that, but I didn’t see many people exploiting hardly any gains. In fact, I saw a lot of people running an airdam without a splitter.
This is a curious pacakge, because most of these airdam-only cars also use a rear wing. It makes for a rear-biased aero solution (gaining more rear downforce than front), which is something I don’t mind, but most people seem to hate understeer and prefer a balanced aero package.
On my own car, I measured a 3.5″ splitter extension at 38 points of front downforce (-0.38 Cl) and 1 point of drag reduction (-.01 Cd). Mathematically, I still believe a 3″ splitter is worth the 3% penalty to lbs/hp. And I’d do some clever shit I didn’t see anyone else doing and make that 3% work like compound interest.
The 2023 rules also added an in-between rear wing to the two existing sizes:
Free – Any rear wing or spoiler under 250 square inches is free. You can conveniently buy a 135cm aluminum wing on eBay for about $60 that is 249.8 square inches or DIY yourself a spoiler. Both of these will be superior to no rear aero, and why not, it’s free.
1% – Any wing between 250 and 500 square inches incurs a 1% penalty to lbs/hp. Many people use a 54” 9 Lives Racing wing, but a 59” APR GTC200 wing also comes in under 500. Personally, I would build a body-width wing and match the chord so that the total was 499 square inches (Miata 64″ x 7.8″).
3% – Any wing over 500 square inches, but less than 701 inches, is legal and incurs a hefty 3% penalty. With the recent 499-wing option, I can see people might not be as interested in the 701-wing, but there’s another stipulation that is you can run a splitter and any wing for 4%. And that’s probably what I would do.
This makes for some interesting choices:
An airdam and small 1” spoiler is the combination with the most power and least drag.
An airdam and medium wing take a 1% penalty in power, but would have significantly more downforce.
An airdam, splitter, and big wing makes the most downforce, but would have a 4% penalty to power.
On my car, which isn’t near the 12.5 lbs/hp ratio power cap, I’d choose the full-aero option. But I could see cars that have to detune or add ballast taking either of the other two options. Which is an acceptable choice, so I can beat them.
That’s all I can remember to talk about, and a wrap on my first Grid Life event. I’m going to continue to pester the organizers to include me in whatever capacity they can use me in, because this is an awesome series and it feels like the future. I’m preparing my Miata for GLTC, and my Veloster for time attack. Yeah, I’m a fucking fanboi now.
I’m going to aero the shit out of Veloster N. This will require serious head scratching at first, and then some DIY fabrication, followed by a lot of testing at low- and high-speed tracks. I expect this process to take the entire summer, with alternating gains and setbacks along the way. But I’ll eventually nail a satisfactory aero package, it’s just going to be a process to get there. So let’s start with the head scratching.
First the stats: I figure my VN weighs about 3250 lbs with me in it, and has about 64% of its weight on the front tires (2080 lbs). The rule of thumb is that aero balance should match chassis balance, and that means a 64/36 split on aerodynamic downforce. This should preserve the car’s natural handling characteristics at all speeds. As a practical matter, this means going after as much front downforce as possible, and balancing that with about half as much in the rear.
I want to figure out what that will do for the total grip of the car. I’ll start with a body that has 0.3 coefficient of lift, and assume that’s evenly distributed (in reality, it’s mostly in the rear, but I’m just doing some rough figuring here). I’ll estimate a splitter gives about 40 points of front downforce (that’s -0.4 Cl) and balance that with 20 points in the rear. That’s not much rear downforce, and I could achieve that with a very small wing, or more likely a spoiler.
Splitter and spoiler add downforce while keeping similar chassis balance.
I want to see what this aero package will do for downforce and grip at different speeds, so I’ll do some rough calculations based on tire grip being proportionate to weight (it isn’t exactly, but these are rough calculations).
MPH
Front DF
Rear DF
Front weight
Rear weight
Front aero balance
Total grip
0
0.0
0.0
2080
1170
64.0%
100.0%
40
20.0
10.0
2100
1180
64.0%
100.9%
60
41.0
20.5
2121
1191
64.0%
101.9%
80
74.0
37.0
2154
1207
64.1%
103.4%
100
117.0
58.5
2197
1229
64.1%
105.3%
120
170.0
85.0
2250
1255
64.2%
107.7%
135
212.0
106.0
2292
1276
64.2%
109.6%
Aero balance same as chassis balance
The results show that the car will gain grip at speed and that the chassis balance will stay pretty much the same. In a 80 mph corner, this would give about 3.4% more grip, which is great.
But I don’t subscribe to the theory that I should balance the aero the same as the chassis. I’ve implemented exactly the opposite of that on my brothers Yaris race car, and had great results. Let’s see how that works out mathematically.
Dynamic rear aero balance
I like a FWD car that is loose in slow corners and tight in fast corners. This makes the car easy to turn in hairpins, neutral in the majority of corners, and stable in high speed kinks. This handling magic isn’t difficult to do, just set up the car to oversteer and use a big wing to shift aerodynamic balance rearward at speed.
There are numerous ways to get a FWD car to rotate easier.
Reduce front roll couple – Softer front springs and/or softer front sway bar; Harder rear springs and/or stiffer rear sway bar.
Tire grip – Reduce front tire pressure or use wider front tires or a softer tire compound. Or increase rear tire pressure, narrower rear tires, reduce rear, use harder tires.
Add rake – Make the car lower in the front or higher in the rear.
Alignment – There are numerous ways to use camber and toe to increase front grip and/or reduce rear grip.
So assuming that I can get the car handling the way I like it in low-speed corners, let’s see what happens when I spec a properly sized wing. In this scenario, I’m going to add twice as much downforce on the rear as the front, and this is about what a typical splitter and wing setup will do.
Wing makes a lot more downforce and shifts balance rearward at speed.
Just like before, I want to see how much grip the car has at different speeds. More importantly, I want to see the aero balance of the car, how much weight moves rearward, and how quickly it shifts.
MPH
Front DF
Rear DF
Front weight
Rear weight
Front aero balance
Total grip
0
0.0
0.0
2080
1170
64.0%
100.0%
40
20.0
40.0
2100
1210
63.4%
102.2%
60
41.0
82.0
2121
1252
62.9%
104.5%
80
74.0
148.0
2154
1318
62.0%
108.1%
100
117.0
234.0
2197
1404
61.0%
112.8%
120
170.0
340.0
2250
1510
59.8%
118.6%
135
212.0
424.0
2292
1594
59.0%
123.2%
Rear-biased downforce.
What the math says is that the aero balance will change about 2% between slow corners and fast corners. That’s like putting 200 lbs of luggage in the trunk, and you’d think that would be noticeable. But the weight shift doesn’t happen that suddenly, and for most corners, I doubt I could feel the difference. In an 80 mph corner, total grip has gone up to 8.1% with the wing, which is a lot better than with the spoiler. But can I use all that grip, or will the car just push like crazy?
Hopefully it works out like this:
In slow corners, the car rotates easily; there should be no noticeable change in rear grip or front aero balance.
In medium-speed corners (80 mph), aero balance should shift about 2% to the rear. This is where I want the car to feel neutral.
In fast corners, aero balance should shift about 3% rearward. I’d like the front tires to be pushing a bit, although I doubt a 1% increase will do that. Maybe I need a bigger wing for that to happen.
At top speed, aero balance should shift about 5% to the rear. I won’t be cornering at this speed, but moving weight, drag, and the center of pressure rearward should help stability when braking.
Now that’s a lot of shoulds, and I don’t usually go in for this kind of rampant speculation. But FWD hatchback aero is mostly unfamiliar territory, and I want to explore the numbers before I build anything. Also, nerding out on this shit is fun.
No splitter, just a wing?
Splitters are a pain in the ass on a street car. In order to make downforce, they need to be close to the ground, and since they also protrude forward, they run aground. The fact is, splitters are just not practical for a daily driver.
So what about using all of this previous conjecture (set up a car to rotate in slow corners and move aero balance rearwards at speed) and applying it to a street car? Could this be as simple as not using a splitter and simply adding a smaller rear wing?
Yeah, it should be. In fact my first project is a DIY spoiler and small wing that attach on the same brackets. I’ll test them back-to-back vs the OEM wing/spoiler and see how they perform.
I was hoping to do my first real-world test this weekend at Grid Life, but it’s going to be wet, and I’m behind schedule on DIY projects. Not a huge loss, I have a lot of dates at WGI this year, and I can do the high-speed testing at the end of May.
Before that I’ve got a track day at Waterford, and I should be able to bring some rear aero options. It’ll be interesting to see if a small amount of rear downforce alone helps at a small track.
I’ve been looking into aftermarket wings for Velosters and thought I’d do a quick review. None of them are super interesting to me, so I’ll do a follow-up article when I make my custom wing.
I’ll start with the OEM wing. It doesn’t have an airfoil shape, the trailing edge is rounded, and there’s no camber to speak of. I doubt it creates much suction underneath, and so it’s not fair to call this a wing. If it’s not a wing, it’s also not a spoiler, as air certainly goes underneath it. If you filled in the gap it would be more effective at creating downforce, but it would also have more drag, which would be a lousy tradeoff on a street car.
Style over substance, but somewhat effective.
But I’m not saying the OEM wing is useless. Most hatchacks create rear lift due to the curvature of the roof, and the Veloster N has about 10 degrees of downward slope in the rear, which is fairly extreme. By flattening out the air at the rear with the “wing”, Hyundai reduced rear lift.
In addition, adding some drag and rear surface area (end plates) moves the center of pressure rearwards. This creates a greater static margin (the distance between the center of gravity and the center of pressure), which makes the car more stable at high speed.
There is more styling than substance here, but at least the Veloster doesn’t have a shit ton of fake vents (ahem, Civic Type R).
On a wing and a prayer
Some aftermarket companies have used the OEM wing as a starting point, which makes sense if you’re trying to sell a product. It would be a lot more expensive to sell a wing complete with a new roof extension, third brake light and window washer nozzle. But while starting with the OEM wing as a base is easier, it results in major compromises. Take a gander and see what I mean.
First, this TIE Fighter wing. It’s shaped similarly to the OEM one, but looks like it has more topside camber. Nevermind that it’s the bottom that needs camber, but you can tell from the fat, rounded trailing edge, that this is cosmetic more than functional. This isn’t a proper airfoil shape, and the end plates are hella stupid. (Usage: The adjective hella is properly used only to modify the word stupid, and then only in relation to people who use hella in a sentence. Example: Dude that wing is hella tight! – No, you’re hella stupid.)
Vader called, wants his ship back.
One thing they did do correctly was make it taller. Wings create downforce via suction, and you need space below the wing for the low pressure region to form. And on that note….
The ADRO V2 wing is a better TIE Fighter. Looking at the underside, it appears to have an airfoil shape, it has a bit of a kick to the topside, and the trailing edges are sharper. They’ve added some height to the middle of the wing, but for some reason not on the sides, which certainly won’t help. Overall, I bet it performs marginally better, but for $1400? Meh and fuck no, all at once.
Shape meant to confuse and distract the enemy?
Next up is the EPSILON+ spoiler extension. At $220, this is the cheapest aftermarket way to make something useful out of the OEM wing (or whatever you call it). By creating pressure on top of the blade and directing air upwards, this locates the rear stagnation point higher, which creates a pressure differential underneath, meaning suction, this makes downforce. There will be some drag increase, but the tradeoff in downforce is worthwhile (for track use). This is also the only OEM option that doesn’t look hella stupid.
EPSILON+ (isn’t that ZETA?) extension.
Clean sheet designs
All of those options started with the OEM wing and had multiple concessions as a result. With a clean sheet of paper, and the roof extension from the base model, what kind of wing could you mount?
The first wing I found was on a first-generation Veloster. The wing mounts are quite nice, attaching to the hatchback door so that you can still get at things inside the trunk. The main problem is that the wing is mounted too close to the roof, and so there’s no room for the low-pressure zone below the wing to form. As such, this is mostly a spoiler in function.
OG Veloster with endplates that are cut out where the low pressure zone is. Like… why?
The other problem here is that this is a 3D wing, but it doesn’t match the profile of the roofline. The whole point of a 3D wing is to make it so that air going down the middle of the car is at the same angle of attack as the outsides of the car (free stream, zero degrees). This 3D wing doesn’t match the roofline very well; the center section isn’t large enough.
I will say that the wing mounts look decent, and I plan to build something similar.
Better end plates, but otherwise same shit, different day.
On the subject of wing mounts, what the fuck is up with chassis mounts on a hatchback? Maybe I’m missing something here, but is there any way to get into the trunk of a hatchback with chassis mounts?
Chassis mount boggles the mind.
Next is a proper wing with proper mounts, and it ought to be, because it’s off a TCR Veloster. I tried to find the specs on this wing and failed, but two things jump out at me right away: 1) It’s set back quite a ways, 2) how did they get the wing to not sway back and forth with those mounts?
TCR wing is proper
First let’s talk setback distance. Increasing setback distance results in more space underneath the wing, and so there’s plenty of room for the low pressure zone to form. On the other hand, the further back you mount the wing, the more leverage it has, which reduces front downforce. Maybe that’s the point of it, to move the F/R balance further rearward?
The mounts themselves only attach at two points, and therefore must have some sturdy backing plates inside, because I can’t see how those are going to keep the wing from swaying back and forth on quick transitions. It’s a TCR car, so I’m sure they have that shit down solid, but I don’t think I’m going to make mine like that.
Next I should be reviewing a 9 Lives Racing wing, but they don’t have one for the Veloster. I’ll have to correct that on my own time. (Meanwhile, I often say 9 Lives Racing “wing”. This is like a litmus test for annoying; anyone who corrects me with “wáng” is a fanboi poseur.)
Next is a wing by CF Style. Mok Racing will be importing these from Korea, and they look like the best option to me. The wing appears to be a proper airfoil shape, and the only nit I have to pick is the lack of a Gurney flap.
Now a Gurney flap isn’t always necessary, the effect is pretty much the same as increasing wing angle. But if you’re cranked all the way up to 10 and you need just a little more, then a Gurney flap is how you get to 11. So some provision for that would be nice to see, as it doesn’t look like a simple piece of angle aluminum will fit that contoured trailing edge very easily.
The wing is mostly a 2D shape, which is fine considering the wing doesn’t stick out into free stream air, or at least not far enough to require twisting the ends down. I don’t have the dimensions or pricing on the wing, but will fill that in when those arrive.
CF Style is an oxymoron, this is function-first design.
If you look at the wing mounts, they appear to be as short as you can make such a thing, and so probably very stiff and light. The setback distance isn’t as far as the TCR, but that may be preferable for most of us, who don’t want to shift aero balance too far to the rear. All said, this wing package is a 98 out of 100, and if I was looking to buy one rather than make one, I’d buy this one.
I look at airfoils a lot, comparing different shapes at various speeds and angles of attack. It’s a nerdy and pointless exercise, because Miatas are limited by front downforce; trying to get the most out of the rear is rarely necessary.
Of the commercially available wings, 9 Lives Racing’s extruded aluminum wing is the best bang for the buck, and nobody is going to feel bad about that purchase. The Big Wang is built apocalypse-strong, and you could probably run a front wing as a bumper. With that strength comes weight, and that’s the only nit I have to pick.
At .2 lbs per inch, a Miata-sized 64” wing weighs 13.2 lbs, and when you add wing mount and end plates it’s close to 20. This isn’t all that much weight considering the benefit you get, so what am I fussing about?
It’s where the weight is. Put that weight down low in the center of the car, and it wouldn’t matter. But put that weight at roof height, at the far end of the car, and that hurts fast changes of direction.
Try this: Imagine running around your yard like it was an autocross track, holding a broom out in front of you. Now do that again with the broom held close to your chest. Much easier! Mass centralization is important for fast changes of direction, and weight at the polar ends of the car, or high up, is bad.
I race a time trials series at Pineview Run, which is a very tight road course with 15 turns in one mile. It’s a bit like an autocross course, but with elevation and camber changes. With so many fast changes of direction, I’ve had better results with a spoiler than a wing. Mathematically, the wing is making more downforce and I should have more grip than when using the spoiler. But the stopwatch doesn’t lie, and I believe the reason for that is entirely the weight and location of the wing.
So I got to thinking about it, and I figured I could build a lighter wing. I’d also make it narrower, which would help a little for mass centralization. But I’d need to increase the chord to so that it had similar overall downforce.
I started with the 9 Lives Racing “Mini Wangs“, which are cutoffs from their factory. I traced the 9LR wing profile onto two pieces of 1/4” aluminum plate, and cut them out on a band saw. I then drilled one side of the Mini Wangs and tapped them for a M6 bolt, and drilled through the other. Next I simply bolted them together. These would serve as my wing supports, as well as the support for my end plates. No welding, easy peasy, and someone could easily do the same upside down and make a swan neck mount.
Wing supports
Next I took a strip of 48″ of aluminum (street sign) and bent an angle on it. This made a 2.5″ extension that I wedged into the 9LR Gurney flap slot. (I had to cut the vertical part of the slot off.) This would act as both the Gurney flap and the chord extension. I used the extension/flap to join the two “book ends” I’d made, and added a center support using another 9LR Mini Wang. For the nose of the wing, I used 1/2″ aluminum tubing, fastened into the bookends and center mini wang.
Next I took a skateboard laminate (single ply of maple that bends easily and takes epoxy well, and I happen to have a lot of these around because my buddy Jason owns Comet Skateboards) and epoxied it over the underside of the wing. I strapped the whole thing down with clamps and let it cure.
Gluing and clamping the bottom
Then I flipped the wing over, added some supports on the inside, and glued another skateboard laminate to the top. I then fiberglassed the whole thing with 6 oz fabric.
9LR wing with 125% chord.
The end result is a 9LR wing with more chord. Ideally I would have made it slightly thicker (to preserve the same shape airfoil), but cut me some slack here; I’m literally gluing a skateboard deck and a street sign to scrap metal.
All told this wing cost me about $70 in materials and a few evenings of labor. But I have a lot of experience with fiberglass and weird shit laying around (like Comet skateboard laminates, street signs, microballoons, etc.), and someone else buying all the materials and having less experience would double the cost and effort.
One Louder
I was trying to come up with a name for the wing. It measures over 11”, which reminded me of the quote from Spinal Tap, “this one goes to 11.” So I’m calling it the Marshall wing, after the guitar amp.
The Marshall has 9% less area than the typical 64″ 9LR you’d put on a Miata, and should have about the same amount of downforce as a 58” 9LR wing. I used a 60” wing on my fastback Miata, so that’s in the same ballpark.
However, at 48″ wide, the ends of the wing are not in free-stream air, and the close proximity of the wing stands and end plates is going to cause more drag and probably some loss in downforce to turbulence. My guess is that behind a standard Miata hardtop, this wing will make 15% less downforce than a regular 9LR wing. Mounted behind my fastback, it’ll be fine.
The important part is that the Marshall weighs just 7 lbs, including the beefy 1/4” wing mounts. This is about half of what a 64″ 9LR wing weighs, and that was the point of this project.
End Plates
If you’ve read my article on DIY end plates, you know that end plates are about the least important thing you can optimize on your car. A good rule of thumb is to make the end plate rectangular, and about as deep as the chord.
I made these end plates from a 10 MPH street sign. I started with a rectangular shape that would leave a number 10 on one side, and the initials MPH on the other. I rounded the bottom corners so I won’t cut my head open reaching for a tool under the car. I made a relief cut on the top to bleed some high pressure air on top of the wing and reduce drag, and then made a cut on the top back corner to lessen the vortex there.
But the real reason I chose this end plate shape is simply to preserve the serif on the number 1. This is how much I care about end plate design these days, I’m letting the sign graphics dictate the shape.
Single wing end plate only goes to 10.
Double Wing – Marshall Stack
My single-element Marshall wing should work for high speed tracks where a reduction in drag might be useful, but I really made this for Pineview Run, where the average cornering speed is in the 40s. For that speed, I could use maybe even more chord and more camber. The easiest way to do this is to stack a second element onto the existing wing. That’s right, I’m calling this the Marshall Stack!
I have a couple made-in-China wings kicking around my shop. I’ve modified the bottom profile to fill in gaps and add roundness, and it’s now a custom profile. I went looking for a similar profile on Airfoil Tools, and the closest I can find is the WORTMANN FX 72-MS-150B shown here at zero degrees. I reviewed that wing in a previous article, no need to go into the details here.
Wortman FX72
Gurney Flap and End Plates
I want to put a Gurney flap on the upper blade. On airplane wings, the standard formula for Gurney flap height is 1-3% of the chord, but on cars you typically see 5% and even up to 10%. The MIC wing has a 5.6″ chord and 5% of that is .28″ which is close enough that I’ll call it 1/4″.
I can adjust the main and secondary wing angles, so I don’t think it’s necessary to have a removable Gurney flap, so I riveted 1/4″ angle aluminum to the top of the wing and called it done.
You may recall that the main wing already has a Gurney flap, it is in fact an integral part of the entire wing structure! But can you use a multi-element wing with Gurney flaps on both wings? Yes. I’ve read a couple scientific papers (1, 2) on the subject, and it definitely creates more lift, but it’s finicky.
There is risk of turbulence and flow separation at the main wing’s Gurney flap, and this appears mostly dependent on the size of the convergent gap between the wings. Which is also dependent on the size of the Gurney flap. To quote Catalano “The use of Gurney flap at the trailing edge of the main element is highly dependent on the gap and overlap optimization.”
To hedge my bets I did two things: First I reduced the size of the main wing Gurney flap to 2% of the chord (about 1/4″); Next I drilled two sets of adjustment holes in the end plates, one to create a smaller convergent gap, and one for a larger gap. I can now adjust the gap size vertically and see which works better.
The secondary wing is supported entirely by the end plates. I made some new ones from street signs following MacBeath’s pressure plot of a double wing.
This image from MacBeath’s Competition Car Aerodynamics. I hope he’s OK with me using it because I always include a link to buy his book. Do it.
To cover the low pressure zone, you can see that the end plate doesn’t need to be extend aft of the upper wing. Most of the low pressure (suction) zone is low and in front of the main wing. My rule of thumb is to make end plates as deep as the chord of the wing, but when I mocked them up, it just looked stupid. I know that larger end plates would probably perform better, but sometimes you have to make concessions for appearances.
MacBeath and others have suggested 2nd element angles of between 20-40 degrees, and so I drilled three holes to allow 10-degree increments on the upper wing.
Triple Stack?
Using another MIC-wing and street-sign end plates, I added a third wing on top. I tested it at Pineview and it worked even better than the double stack. But it looks so fucking ridic I’m embarrassed to be seen with it in public.
But this construction method proved strong and light, and my next project is a 3D wing for my Veloster N. Subscribe to the blog if you want an update when that happens.
I just bought a 2022 Veloster N, 6-speed manual. Naturally I’m going to aero the shit out of it, which will bring new hatchback content to this site. All of the Veloster articles will be tagged with “VN” in the title for easier searching (and so Miata people can ignore it).
Why a Veloster N?
Last August I decided I wanted a new car because driving a couple hours to and from a track in my Miata was loud and uncomfortable. Yeah, I’m that old. I put a deposit on a 2023 BRZ, but after 6 months of hearing nothing from the dealership, I got my deposit back. It wasn’t just the waiting game, but I realized I don’t want a Subaru engine in anything, and I also want a front-wheel drive sports car for a change of pace.
I’ve owned several FWD cars in the past (Corolla Tercel, EF Hatch, EF wagon, 10th gen Civic, Mini Cooper), and have raced my brother’s Yaris a number of times, and FWD has different capabilities that makes driving interesting. Compared to RWD, FWD is faster in the wet, better in the snow, but is generally slower on track. At Pineview Run, FWD is really fucking slow for some mysterious reason. And therein lies the challenge.
I did a lot of research on FWD sports cars and my top three were the Veloster N. a K24 Civic Si and a Mini Cooper S (or Coupe). The Veloster N is certainly the fastest, but more importantly, it reminds me of the CRX I always wanted in my youth.
The shape of things to come.
I’ve tracked a couple
I’ve driven a couple Velosters at Pineview Run. One of my oldest and bestest friends, Chris Gailey, has let me track his VN at Pineview. The car impressed the hell out of me, and I reviewed it and other cars in Driving Other People’s Cars in 2020, and said this about the VN:
If I was going to buy a new car tomorrow I’d buy a Veloster N. This is coming from a Miata guy who was teetering on quitting racing and buying a ND2. Yeah, the Veloster is that good. I would roll the fenders flat and fit the widest 18″ wheels and tires that would fit, add a splitter and a wing, and fucking dominate.
It took three years, but the plan remains pretty much the same. Except that it’s not easy to fit really wide wheels and tires. Most people have only increased the width by half an inch and are on 18×8.5 +45, and use a 235 or 245/40r18. I waffle back and forth on which way to go on 18″ tires, but if history has taught me anything, then I’ll probably have a dozen wheels in my basement this winter.
On the OEM Pirelli PZ4s I was able to do a 1:17.767 at Pineview Run. I’ve gone a couple ticks faster in my Miata on Continental ECS, and so around this tight track, the VN isn’t any faster than a modified NA6. On Falken RT660s I did a 1:15.565, which is a bit faster than I’ve done in my Miata on RS4s, so again, the Veloster is probably slower than my Miata on equal tires. I suspect this will only hold true at Pineview, and at longer tracks the VN will come into its own.
But check this out, driving that bone stock VN on RT660s, I was only .25 seconds away from the all-time FWD lap record! As a data point, here’s me driving a VN at Pineview on the OEM PZ4s (red) and RT660s (blue). Lateral grip was better on the Falkens, but I also backed up the corners a lot better.
Lateral Gs and speed trace for Veloster N at Pineview Run on PZ4 and RT660 tires.
Admittedly the VN isn’t a Pineview car, and I bought it mostly for coaching at bigger tracks like NYST and Watkins Glen. I’ll be data coaching at those tracks a dozen times this year, but I also want to hit a few tracks that are further away.
Meant for track use
The N stands for Nurburgring, because that’s where the car was developed.
The user manual doesn’t have a bunch of warnings about not driving on race tracks, it assumes you will.
Proper.
Warrantied for track use
Back in the day you could change the brake fluid and brake pads to higher temp versions and track just about any car. These days it seems like every car overheats on track, has nannies that spoil the fun, or is otherwise unsuitable for track use. Many new cars also stipulate that if you track them or compete in a timed competition, you void the warranty. This even applies to autocross.
There aren’t many new cars that are warrantied for track use. I believe all Porsches are, the Camaro 1LE is and… the Veloster N. From the factory: “Since the Veloster-N was designed for high performance at home or on the track, track utilization alone does not void the warranty.”
Most track cars get modified a little, and if you reprogram the ECU or use a piggyback, install an aftermarket blow-off valve, increase boost, change the turbo, etc., that will void the Hyundai warranty. But you can add a cold-air intake, bigger intercooler, oversized throttle body, and things like that and you’re still covered under warranty. I’m going to drive it without any mods, as it already has 275 hp (about 235 to the wheels according to most dynos), and that seems like more than enough.
Hyundai has a 10-year, 100k mile powertrain warranty, and because I got a Hyndai-certified used car, I was able to get bumper-to-bumper coverage for that entire duration. This is based on the original purchase date of the car, so I can beat the living shit out of this car until November of 2031 and if anything breaks, it’ll be someone else’s problem. That’s pretty incredible, and maybe more of a reason to own this car than everything else put together.
Insured for track use
I did the most adult thing I’ve ever done: bought track insurance. I used a company called OpenTrack because they have an annual policy, whereas Lockton and Hagerty are a la carte, and would require a new purchase every track day.
Total cost was about $3100 for the year, with a 5% deductible. This covers me for unlimited track days in my Veloster and my Miata, and a second driver. Wait, what?!? For realz. I can specify a second driver for any event and they are covered in my car as well.
Pre-delivery purchases
I’m still waiting for the car to arrive, but before that, I’ve already purchased a few things:
Brake pads – I don’t like the squeal of race brakes, and prefer a pad with a lower mu, but I also need high temp resistance. I used to get StopTech 309-series pads, but since changing manufacturing plants those pads are now utter shit. So in the end I went with Porterfield R-4E, which is a pad I’ve used before.
Tow hitch – I may tow my motorcycle or a teardrop trailer, or add a bike rack. The hitch is also a good jacking point, and I might find a way to use it as a base for a diffuser.
Base model spoiler – I’m going to add a big wing in place of the OEM one. The base model Veloster has a simple roof extension without a wing, which won’t compromise my mounting options.
Camber bolts – High performance tires require a lot of camber, and I’ve read that people have damaged the OEM shocks by using adjustable top hats. Crash bolts don’t seem to have the same problem, but also don’t allow as much negative camber. The bolts do reduce inner suspension clearance slightly, so this may affect future wheel decisions.
Oil cooler – If the engine breaks in the next 10 years, Hyundai will fix it, but it’s still worth taking care of. An oil cooler should help everything last longer, so I splurged on a nice one.
Wheels and tires – For dedicated track use, I got Konig Countergram 18×8.5 +43 wheels and Kumho V730 235/40r18 tires. Most people seem to go with 245, but 235 is closer to the standard diameter, and wider tires are not always faster.
Once I receive the car I’ll do some shakedown runs at the local tracks (NYST, PV, WGI) and get baseline data. And then the aero fun begins.
A splitter separates airflow above and below the car, reducing drag and lift by decreasing the amount of air going underneath the car. A splitter also creates downforce via pressure on top of the splitter blade and suction below the undertray. Like a rear wing, the suction side is much stronger than the pressure side.
When I look at splitters on typical track cars, I see a lot of mistakes, mostly because people don’t understand that creating suction underneath is more important than everything else a splitter does.
Now you’ve seen people who put wings really low on the trunk lid, with the result that very little air goes under the wing. Moreover, there’s no space below the wing for the low-pressure region to form, and so the wing doesn’t perform as it’s supposed to.
A wing mounted too low is a spoiler. A splitter mounted too low is just as bad.
When a wing is mounted that low, it behaves as a spoiler, creating downforce through pressure, and not suction. If you mount your splitter too low, it does the exact same thing. But most people don’t know that, and make all sorts of mistakes by not optimizing the underside of the splitter.
Given that major misconception about which side of the splitter does the most work, let’s talk about how people mess up their splitters, and how to get the underside working for you.
Now before I do that, I have to admit that I’m as guilty as anyone when it comes to splitter mistakes. In the past, I really only considered splitter length and ground clearance, and those were mostly for durability. After taking the JKF Aero course and understanding CFD pressure plots, I have a much better understanding of the mistakes I made, and hope to help my readers avoid the same ones. Such as…
…sharp leading edges
Aerodynamic wings (airfoils) always have a rounded leading edge. Air must flow around either side of the stagnation point at the front of the wing, and stay attached along the entire surface.
Airfoils come in all shapes and sizes. All of them have a rounded leading edge and sharp trailing edge. Your splitter should be the same.
Sharp leading edges cause flow separation, which results in drag and turbulence. If you want a really shitty wing, turn it backwards so that there’s a sharp leading edge and a rounded trailing edge. You’re not going to do that with a wing, but you might be doing that with your splitter!
Sometimes sharp leading edges are a consequence of the material, such as when using aluminum or carbon fiber. But if you’re going through the trouble of making a splitter from composite materials, you can certainly go through the trouble of thickening and then rounding the leading edge! When you round the leading edge of your splitter blade, round the bottom of the splitter blade more than the top, obviously.
Just say no to sharp leading edges.
On high-end sports cars, I see a lot of aftermarket splitters that are super thin, made from carbon fiber, and costing thousands. Something that expensive makes you believe it works as designed, but that sharp leading edge creates flow separation, no matter how much you paid for cognitive dissonance.
…too low
There was a recent conversation on a Facebook Miata group regarding splitter height. One internet pundit gave everyone else the benefit of his inexperience by stating that you should run the splitter as close to the ground as possible. His reasoning was that the splitter keeps making more and more downforce the closer you get. That’s not entirely accurate.
Yes, downforce increases as the splitter gets closer to the ground, and the gain is fairly linear. However, from around 3” to 1.5”, downforce increases sharply, and that’s where you want the horizontal portion of the splitter (measured with driver, full fuel tank, and at speed). If you go lower than 1.5”, you start to get flow separation, which results in drag and a drastic reduction in downforce.
To put some round numbers on it, let’s say your splitter makes 80 lbs of downforce at 6″ of ground clearance. It will make about 135 lbs at 3″, and max out at 200 lbs at around 1.5″. If you go lower than that, the situation reverses and the splitter loses downforce dramatically until its back to 80 lbs at .75″. If you run your splitter half an inch off the ground, it produces the same downforce as eight inches off the ground!
Flat splitter blades are easy to build, but are more sensitive to height. You’ve seen splitter blades that are higher in the middle than on the sides. The purpose of this is twofold: To get more air volume under the center of the splitter to create more downforce, and to mitigate detrimental effects of sudden changes in ground clearance.
Let’s dig into that second part. Let’s say you have a flat splitter that’s 1.5” off the ground making 200 lbs downforce. Then you hit a bump or pitch the car forward such that the blade is now just barely off the ground – the splitter loses most of its downforce. The car now rebounds upwards on its springs, back to where it was making maximum downforce, which pushes back down again. Repeat that process and you have porpoising.
Having a splitter blade that has a higher center portion means you don’t get the same maximum downforce, but you also won’t get into a situation where the car suddenly loses (or gains) large amounts of downforce with sudden changes in ride height. A raised center is essentially hedging your bets. So you can see how important ground clearance is to splitter performance.
To the people who run their splitters as close to the ground as possible, I want to race you. For money.
…unsupported
Airdams and front lips don’t create much downforce unless there’s planform area of low pressure under the car. In other words, the front lip needs to be connected to, and supported by, a horizontal component. Factory or aftermarket front lips that aren’t connected to a rigid undertray only create a tiny (negligible) amount of downforce.
On NA Miatas, the R-package front lip is a popular add-on. This will keep some air from going under the car, and in that way can reduce drag and lift. Larger versions like the Garage Vary (GV) front lip also can build a small amount of local pressure on the convex portion, but it won’t be much.
Unsupported front lips look cool, but do very little to create downforce.
This kind of unsupported front lip is the only situation where you’d want to run the aero as low as possible. You won’t lose downforce because you haven’t gained any, and less air under the car is better. But compared to a proper splitter, these cosmetic doodads aren’t really an aerodynamic device, they are just for show.
Attaching a front lip to an undertray is far better, because then you can add splitter diffusers and other tricks to make real downforce via suction. A car set up like that would be a real sleeper – looking stock, but performing far better.
…flexible
Splitters can create more than two hundred pounds of downforce, so the blade needs to be rigid. I see people standing on their splitter blades and that’s an OK benchmark for how strong the lip needs to be. And yet I’ve seen so many amateur splitters (both DIY and aftermarket) that would flex under the weight of my big toe.
Case in point, a guy I met at Miata Day (Canaan, NH) who had never been on track before. Like many street enthusiasts, he had a very “appearance grade” Miata with eBay aero tacked on everywhere. His spitter was so flimsy I could deflect it with a touch. I told him he should remove the “splitter” or he was going to lose it in the first session. He lost it.
Now before you go building a splitter out of 1” plywood so that you can stand on it, note that the low-pressure area is about 1/3 of the way back from the splitter lip. It’s not the front or the top of the splitter that is doing most of the work, so you don’t need to be able to stand on your splitter blade, you just need to keep it from flexing at speed.
…shitty materials
Plywood is probably the most common splitter material. Regular exterior plywood from your lumber yard is junk: it’s heavy, has knots and voids, very few plies, and delaminates when wet.
Sometimes you can find a better quality of plywood, such as oak or birch, but often only the outer veneers are better wood and the inside is the same knotty, void-ridden, pine-based shite in the exterior plywood racks.
If you look hard you can get true Baltic Birch, which is a furniture-grade wood with a good strength to weight ratio, and lots of thin laminates. But I’ve seen Baltic Birch splitters delaminate, and suspect the glue is usually the water-soluble type.
To avoid delamination, plywood splitters need to be made out of marine plywood. Marine plywood has different grades, and what the “marine” distinction really means is that the glue is waterproof.
I once ordered a sheet of 3/4” marine plywood from my local specialty lumber store. What I got was a 80-pound slab of 5-ply Douglas Fir. I returned it immediately. A similar sheet of Meranti plywood weighs 64 lbs, has 11 plies, and is stronger.
The ideal wood is certified boat building plywood. There are two grades, BS1088 and BS6566. 1088 is an appearance grade, more expensive, but generally easier to find. 6566 isn’t as pretty, but is built to the same specification. The BS specification is void free (X-rayed, I believe), and boil tested for delamination.
I like Meranti BS6566 Hydrotek made from mahogany. There are other BS-certified plywoods made from sapele, gaboon, and other hardwoods, and some of them are lighter than Meranti, but none of them are cheaper or better. For example Okume is about 10% lighter than Meranti, but it’s also more flexible and more expensive, and so I don’t think it’s better for splitters (for boatbuilding it’s superior).
I typically make my splitters from 9mm (3/8) because I like them light and I brace them accordingly. For an endurance team catering to the arrive and drive crowd, I’d spec 15mm for the extra durability. And 12mm (1/2”) is right in between and a great compromise for most uses.
You can also make a splitter from aluminum, Alumalite, carbon fiber, etc. Sheet aluminum is heavy and has a sharp leading edge, and I wouldn’t build a splitter out of solid aluminum.
Alumalite is a common splitter material, it’s two very thin layers of aluminum bonded to a lightweight hollow plastic core. The material is mostly used for street signs, but has wound up underneath a lot of budget race cars as a flat bottom, or as a splitter.
I have an Alumalite spoiler, and I’m not sure why people love this material. You can’t weld it, it doesn’t glue well, it’s more difficult to work with, and it’s not particularly light. A square foot of 10mm Alumalite and 9mm Meranti weigh the same and the Meranti is stiffer, more durable, easier to fix, and half the cost.
I once made a speargun out of carbon fiber, and the layup process isn’t that complicated. If I had unlimited funds I’d build a splitter from carbon and Kevlar, but for my current situation, I don’t think a 5 pound savings is worth it.
…exposed ends
Time-attack cars often have splitters with “hammerhead” extensions on them, which are wider than the car. When properly constructed, these extensions are wing shaped in profile and cause air to move upwards, which creates pressure on top and (more importantly) suction below the splitter extension.
On Miatas, I often see smaller splitter extensions that are basically unused splitter material, they are horizontal and don’t change the direction of airflow. Here’s the thing: if you don’t change the direction of airflow, you aren’t doing dick. A flat horizontal plate just increases frontal area and causes drag. Why have a splitter that’s wider than the bodywork if you aren’t using that in some meaningful way?
Exposed flat splitter blade does nothing.
I sometimes see these exposed splitter ends coupled with an endplate or spill board on the outside edge. The first thing I always think is, “this is going to get caught on grass and rip the splitter off.” For the life of me I don’t understand why people do it, as there are better uses of that space.
I’m not saying it’s useless: a spill board acts as an air curtain, directing air along the side of the car. This can reduce the wake of the front tires, and reduce drag of the car as a whole. For an endurance racer that’s right on the cusp of being able to skip a fuel stop, you might choose less drag over more downforce, but the drag reduction is tiny.
On a street car doing 15k miles a year, reducing drag can be useful, but for a race car, it’s better to kick the air upwards or out sideways.
If you have some extra width on your splitter, by all means make a vertical back wall. This will create a high pressure zone on the top surface, generating downforce. That spat will also send air up and out, creating a suction zone under the splitter extension, creating even more downforce.
I wrote about this in Splitter Length and Side Fences and you should read that if you haven’t. The gist of it is that MacBeath tested spats of different shapes and sizes in a wind tunnel, and a vertical spat increased front downforce by 150% and had the best L/D ratio. The car was an Integra, not a Miata, but you can imagine the results would be pretty similar. Now that’s using the exposed splitter end to good effect.
You can put a fence on the outside of that vertical spat, which will capture more local pressure (more downforce), or leave it bare, which will kick air out sideways. Directing air outwards will help prevent air from intruding beneath your splitter, and helps extract air from the wheel arches, which in turn makes your splitter more effective.
Whether it’s better to kick air up or out is debatable. There are downstream effects of both, which you could estimate in CFD or test on track. But surely, however you direct the air off that extra splitter width is better than leaving it unused.
…no diffusers
By now I hope we’re all on the same page and agree that splitters make downforce by creating suction underneath. Suction increases if you allow air to expand behind the splitter. You can do this to a small degree by rounding the underside of the front edge and tapering the trailing edge upwards, creating a curved surface.
Better still, rake the splitter upwards at the rear, or drop the front if you have the ground clearance. You can’t normally get more than a degree or two by doing this (subframe, oil pan, and other things get in the way), but if the rules don’t allow tunnels, this is all you’ve got to work with.
If the rules allow it, or if you simply have a track car unbound by racing rules, absolutely install splitter diffusers (splitter ramps) underneath the splitter. The concept is the same as a diffuser behind a car, it allows air to expand, which accelerates the air in front of it, creating more suction.
Splitter ramps can be 3D-printed into a continuous curve, or just an angled ramp of sheet metal. If you go the latter route, don’t exceed a 12-degree angle, or you risk flow separation. If you don’t have an angle meter, that’s about a 2.5” rise over 12” run.
Splitter ramps from scrap aluminum.
If you buy 3D-printed splitter ramps, beware of what you’re buying. I just saw someone in the Miata 3D printing group who is trying to sell a product with an 18-degree slope. That’s too steep and will cause flow separation. His price was also too steep, considering you can make your own out of scrap metal for a dollar.
Verus Engineering splitter diffusers are legit, but you can DIY something for a lot less.
Where you place the splitter ramps depends on where you can get the required height for them. Generally you can dump air into the wheel wells as there’s room to work with and it’s a fairly lossy area to begin with. But if you dump air into the wheel wells, you need to extract it.
And on that note….
…bleeding air underneath
Nature abhors a vacuum; if you have suction underneath the splitter, then air from everywhere else is at a higher pressure and wants to hate on it and spoil the party. To make the splitter perform at its peak, you need keep the bad air out. And yet, I often see cars that make no attempt at keeping air from bleeding air into the low-pressure zone beneath the splitter.
The largest source of this air comes from the engine compartment. Think about it: all the air that goes through the radiator has to go someplace, and it often goes under the car. If this air can wrap around the sides of the splitter, it ruins the suction you’ve worked so hard to create. So the best way to mitigate this is ducting the radiator and using hood vents. Hood vents aren’t just for cooling (or looking cool), they make downforce.
Vents on top of the fender and extractor vents behind the wheels will also relieve pressure in the wheel arches that’s trying to get under your splitter. If you have splitter diffusers, you’ll need as much venting as you can get.
Both hood vents and fender vents should ideally eject air upwards, thereby creating an opposing force, downforce. Unfortunately the downstream effects of these vents is turbulence, and with that, a loss on rear wing performance. But since most cars are front limited with respect to downforce, it’s a good tradeoff, just use more wing.
Downstream effects of venting.
Getting back to the situation under the splitter, another area of loss is air that comes in through the wheel spokes. Optimizing this area doesn’t provide a lot of benefit, but it’s worth going after if you’ve done everything else already. If you take the JKF Aero course, he goes into a lot of detail on caketin covers, and it’s beyond the scope of this article, so if you’re looking for the last bit of performance, take the course.
…cooling ducts too low
So far I’ve concentrated only on the underside of the splitter, but the top of the blade also matters. There’s a recirculating bubble of high pressure air on the top of the splitter blade, and you want to hold it there. For the people that ignore what’s happening underneath the splitter, this is the part of the splitter that matters to you.
If you place vents (radiator inlet, intercooler, brake ducts) low down on the airdam/fascia, that high pressure air goes through the holes instead of being held on the blade. Directing air into ducts might be beneficial for cooling, but it reduces the downforce.
A radiator opening this low will make less front downforce, and air has to bend sharply upward to get to the radiator. Radiator openings should also have rounded corners for attached flow.
The other problem with a radiator duct that’s too low is that air has to bend upwards to get to the radiator. If that angle exceeds 12 degrees, you’ll get flow separation (drag, turbulence, loss of velocity and cooling ability) inside your air duct. You’ll get better cooling and less drag with a straight shot to the rad, and you’ll create more downforce by holding pressure on the splitter lip.
If you’re racing in a series that doesn’t allow you to use a splitter, but allows an undertray, you could use an arrangement like the pic above (imagine the airdam and undertray being flush, with no splitter extension). This would allow you to hold some pressure on top of the undertray and make suction below. In that case, I’d certainly put the radiator opening at the bottom and trade downforce for the consequences.
Your splitter sucks!
The purpose of this article was to point out the most common mistakes people make with splitters, and to tell you that your splitter sucks. Literally. It sucks to the ground and that’s where most of the downforce comes from. I see a lot of aftermarket and DIY splitters that could be easily modified for less drag and considerably more downforce.
Now that you know that your splitter sucks, take a look at it with fresh eyes and ask yourself how you can optimize what’s going on underneath. What can you do to make your splitter suck even more?
There’s a scene in The Road Warrior where Max hits a switch on his shifter and his supercharger spins up, giving him an extra boost of speed. I’ve always wanted something like that. Or rather, I want something more effective than turning off the A/C.
It makes a noticeable difference.
The aerodynamic equivalent of that is a DRS system, like on Formula 1 cars. In F1, the upper wing of a dual-element wing can pivot into two positions, one for downforce, and one for low drag. It works, and makes F1 racing a lot more fun to watch. But you don’t see active aero much in other racing series, which is a shame, because racing improves the breed.
Since active aero is largely banned in racing, most of the advancements are happening on street cars. The first street car with active aero was way back in 1986, the exotic and unattainable Porsche 959. But just two years later you could get an active spoiler on a pedestrian Volkswagen Corrado.
Corrado active spoiler.
And two years after that, the Mitsubishi 3000GT had active aero on both ends! A Russian magazine did some testing and reported that front lift reduced by half, and rear lift became actual downforce. This reduced top speed by 5 mph, which is an acceptable trade.
Russian spy data on Mitsubishi 3000GT active aero.
Those cars are now considered vintage, and on modern supercars like the Pagani Huayra, active aero is much more sophisticated.
Pagani Huayra active aero.
Given unlimited resources and time, I’d develop a system that changes around the track based on GPS points: On the straights the aero would settle into the position of least drag; In braking zones the aero devices would move 90-degrees to the wind and behave like a parachute; In corners, the aero would pivot into the position of max downforce. I’d also have rudders and vanes on the sides of the car to help bank it into turns, loading up the tires differentially and using air resistance for turning.
But bringing this back to reality, I’d start with something simple, like the VW Corrado spoiler. I’ve got a pair of Miata pop-up headlight motors on a shelf that I’m saving for just such a project. I’d hook them up to the headlight toggle switch on the dash, which would give me a high downforce setting I’d use for most of the track, and a low-drag DRS setting for straight line speed.
Before I embark on that journey, I’m going to look at a few aftermarket active aero systems, and then run some simulations to see how much active aero is worth.
NINTE Lifting Spoiler
I’d never heard of NINTE before writing this article, but apparently they make active aero for many sedans. You can tell from the shape and the integrated 3rd brake light that this is not a wing – they really don’t care what the underside is doing.
Active spoiler.
The spoiler rises up automatically when speed reaches 60 km/h, and descends automatically after 10 seconds when the speed drop down to 30 km/h. You can also control it manually.
In general, I’m a fan of spoilers on street cars, because they reduce drag and lift, and cars look better with them. Aesthetically, I like simple spoilers and this one is not. But at $850, it’s not outrageously expensive for something that could be fun and different.
Active Miata Wing
Carbon Miata sells an active wing for Miatas. It’s a three-position system for DRS, normal, and airbrake. The motors and levers are exposed and the entire thing has a DIY look about it. Normally I’d dig that, but if I was shelling out $3k, I’d want a more professional look. I think they could have hid the motors on the underside of the trunk lid or something.
Exposed motors don’t do much for the looks of it.
The airbrake mode is interesting, it tilts the wing to 90 degrees and while I believe it would be effective, it also scares the shit out of me. With the wing in airbrake position you’d lose rear downforce, but you’d move the center of pressure rearward and get a lot of drag to boot. I wonder how much stress the system can take, and if it’s designed for fast racetracks or just autocross.
Airbrake activated!
The carbon wing looks quite nice, and even if you never used the airbrake mode, the standard setting and DRS would be useful.
TRK1 Active Aero Smart Wing
If you have $3500 bucks lying around, you might want to try the SPT 1 Smart Wing. The wing comes in different sizes from 58″-70″, and has five downforce settings, low-drag, three downforce levels, and airbrake. The downforce levels can either be preset or programmable.
If you opt for the presets, you get three downforce levels: 10 mph, 50 mph, and 80 mph, plus the low drag and airbrake settings. If you buy the CPU version, you can program the wing to change angle at any three speeds you want.
The wing looks nice and the active aero strut is unobtrusive.
For example, you might set the wing for low downforce at speeds up to 40 mph, to help the car rotate in slow corners, then transition to a maximum downforce setting up to your fastest corners, say 80 mph, and then start dropping wing angle at 100 mph, and go into full DRS mode at 120 mph.
You set the airbrake based on longitudinal Gs. Now I imagine this one would be a little tricky to set up, because just lifting off the gas will give you around .3 G of deceleration, and there are times when you want to lift and brush the brakes slightly, but still retain maximum downforce and grip. In such a situation, you wouldn’t want the wing to pivot into airbrake mode. So maybe after some experimentation you’d find that around .6 or .7 G translates to straight line braking, and that’s when you’d activate the airbrake.
It all sounds very high tech and fascinating, and one wonders what it would be worth in a lap time. The manufacturer claims that their single-wing DRS system was 10 mph faster than a fixed wing when tested on a Shelby GT350 at COTA. I’m not going to call total bullshit on them, but if F1 cars get only 7 mph out of a double-wing DRS system, it does sound a little far fetched.
OptimumLap simulations
This is Occam’s Racer, where we do simulations and pretend it’s meaningful. In this make-believe world, I’ll do the simulations at Watkins Glen. The straights are long enough to use active aero, and in the real world, the track is only 25 miles from me, so I might be able to test this for realz one day.
You might want to skip ahead to Single element wing. The rest of this section recaps how I made an error in the simulations, then figured out a more accurate way to measure DRS, and a neat trick in OptimumLap to see small deltas.
The first time I ran the simulations, I cheated: I simply took a wing and reduced its drag value, reckoning that this was the same thing as active aero. It’s just less drag, right? Wrong. I immediately saw my error because the active aero wing had a lower top speed than the low-drag wing. The reason is, the car weighs less in when the wing is in a low-drag setting. Wings make downforce, which is the same as weight. So I had to scrap everything and start over.
To properly simulate active aero, you have to take into account not only drag reduction, but weight reduction. To do this required increasing mechanical grip of the low drag wing, such that it matched the exit speed of the high downforce wing. And then I had to determine the amount of time from corner exit to the braking zone between the active wing and the low drag wing. Good fucking god that was a lot of work!
And not to get too far ahead of myself, but the values were tiny, and difficult to see in the data. However, in doing these simulations, I found out something useful, which is that you can easily zoom in or out in OptimumLap. If you draw a rectangle on any of the charts starting in the top left and drag to the bottom right, it zooms in. Do the reverse and it zooms out.
Using this method, I was able to zoom into the time-distance graphs and get the exact amount of time it takes to cover any amount of distance on track. By subtracting starting and ending points, I then got the delta for how much faster the low-drag setting was. Ugh, tho.
Single element wing
On a Miata, you typically run a single element wing at 3-5 degrees angle of attack. Air comes down the roofline at an angle, which puts the middle of the wing at around 10 degrees. Most wings will stall at more than 10 degrees, and so you don’t want to set the wing with much more angle than that. A wing set like this adds 3 points of drag, so if your Miata has a Cd of .45 without a wing, it’ll be .48 with a wing.
In the low-drag wing configuration, the car would have a Cd of around .465. This is really the best you can do on a 2D wing, as the ends of the wings are always 5-7 degrees offset from the middle of the car, and a properly set up wing doesn’t have a lot of drag anyway.
Watkins Glen has eight potential DRS zones: the front straight, the back straight, and the short straights between the corners. In those DRS zones, I’d have to push a button to lower the wing after exiting each corner and then push the button again to raise the wing before the start of every braking zone. Sixteen button pushes would take some concentration, and I might find my lap times were worse using DRS.
Instead I’m going to say that there are three DRS zones: front straight, back straight, and between turns 7 and 8. I’ve added 10 lbs to the car with active aero, to account for motor and levers.
I’ll simulate going around the track three times. Once with the wing fixed in the low drag position, another time with the wing fixed in the standard downforce position, and then using active aero in the three DRS zones. Here’s the lap times:
Wing
Low drag
Standard
Active aero
Lap time
2:18.12
2:15.28
2:14.92
Fixed wing and active aero configurations.
The slowest configuration would be the wing set to the lowest drag setting. This corresponds to the wing set for maximum efficiency, which is why choosing a wing or angle of attack based on its efficiency is meaningless.
Setting the wing to the standard 3-5 degrees angle of attack makes the L/D ratio of the entire vehicle the most efficient. This is faster than the low-drag setting by almost 3 seconds.
Finally, the active aero wing would be about 0.36 seconds faster than a fixed wing. Now wait a goddamn minute… that’s it? Yep.
Single element wings are efficient at producing downforce and do so with very little drag. In fact, a wing has about the same amount of drag as your two side mirrors combined. Thus, active aero on a single element wing is about as effective for drag reduction as if you moved one of your mirrors inside the car on the straights.
Given that, is active aero worthwhile? For causal lapping at a track day, notsomuch. In a racing situation, sure.
At Watkins Glen, the back straight is where drag reduction makes up the most time. From the exit of Turn 2 to the braking zone of the Inner Loop is about 3000 feet. Setting the wing into the low-drag position makes the car go 1.5 mph faster, and gains 0.17 seconds per lap over a fixed wing.
Speed trace from Start/Finish to the braking zone for the Inner Loop.
But a better way to visualize that is that DRS gains about 25 feet on the car with a fixed wing. So with two evenly matched cars racing close together on the back straight, the car with active aero should be able to pass the car with a fixed wing.
And that’s pretty much how it happens in Formula 1. The trailing car activates DRS and makes a pass on one car at the very end of a straight. Speaking of F1, wouldn’t a dual element wing be a better usecase for active aero?
Dual element wing
Dual-element wings aren’t as aerodynamically efficient as single wings. As you add elements, you gain downforce, but you gain drag at a higher rate. However, because the wing contributes a very small amount to the overall drag of the car, the aerodynamic efficiency of the vehicle is better with a dual wing. As I’ve simulated it, the aerodynamic efficiency of the single-wing car is 2.08, and the dual wing is 2.98.
The first simulation I’ll run is a fixed single wing versus a fixed double wing. Despite a 2 mph slower speed on the back straight, the double wing is about 1.5 seconds faster than single. It makes up time in every corner and keeps that speed onto the shorter straights.
Speed trace of a double wing (green) vs single wing (blue).
So now I’ll make the upper wing active and it goes .60 seconds faster than a fixed dual wing. Here’s the lap times:
Wing
Singlewing
Double fixed
Double active
Lap time
2:15.28
2:13.86
2:13.26
Fixed wing vs double wing vs double active aero.
That’s not too shabby, and most of the gain is on the back straight. Activating DRS on the run from T2 to the inner loop is worth .35 seconds alone. This is a gain of over 50 feet of track on a car with a fixed dual wing. So as you can see, active aero makes more sense for a dual-element wing than a single wing.
So how come active aero isn’t as effective as we see on TV? Mostly because F1 cars are so damn fast. Drag force doubles with the square of speed, so there’s four times as much drag at 200 mph than 100 mph. At autocross speeds, drag is inconsequential, but at high speed it’s a game changer. Even so, on a F1 car, DRS is only worth about 6-7 mph. So it stands to reason that a dual-element DRS wing might be worth only 1.5-2 mph on our cars.
New York Safety Track
Watkins Glen is a long, fast track with a higher top speed than any other track I’ve been on, and represents a DRS best-case scenario. I also simulated what would happen at New York Safety Track, because it has shorter straights and a lower top speed, and is more similar to the average road course. I also coach at NYST several times a year, so if I build a DRS system, I’ll be able to test it in the real world as well.
NYST has just one DRS zone, the 1400′ front straight that they use as an airstrip for small planes. I only simulated the dual-element DRS wing, as it was the most effective.
If I activated the DRS system at the exit of T18, I’d gain .058 seconds to the Start/Finish line, and from there to the braking zone for T1, I’d get another 0.062 seconds. All told, DRS would be just 0.12 seconds faster than a fixed dual wing. In terms of top speed, it’s a difference of less than 1 mph. That’s enough to make up only one car length against an evenly matched fixed wing car, and would be of dubious benefit.
Conclusions
Active aero is typically banned at the club racing level, and after doing this theoretical investigation, I’m inclined to agree with that restriction. Active aero adds weight and complexity, and mechanical things fail mechanically; I can only imagine the jank that me and other DIY pioneers would litter the track with.
Now if you’re racing in 24-hours of Lemons, go ahead and make an active aero system and see if it’ll pass tech. Or build an anti-aero device that makes a jack-in-the-box pop out of your roof. But for serious racing, you’ll achieve more by reducing drag anywhere else on your car.
Think about it: if you want to reduce the weight of your car, you don’t look at all your carbon fiber components and try to lighten them. You go after the parts that weigh the most.
Wings are already designed for optimum performance and low drag. Reducing drag on what is already the most aerodynamic part of the car, is as silly as trying to lighten what is already made out of carbon fiber. Your hardtop, cooling system, mirrors, wheels, rear surfaces, and everything else on your car are better places to concentrate on drag reduction.
For HPDEs, there’s even less to be gained with DRS than in racing. Moreover, I ran these simulations at a very fast track with three long DRS zones. Most race track have fewer and shorter straights, and DRS would be worth only a tenth of a second.
Just the same, I’m pretty sure I could build a robust DRS system. And I have those headlight motors just sitting there on a shelf. And it’s still over half a second at WGI that I’m not going to get anywhere else….
Addendum: Spoiler
The first simulations I ran were with spoilers, but once I realized that I’d made incorrect assumptions, I didn’t bother recalculating the lap times to the same level of detail as I did with the wings. However, someone might be curious about the effectiveness of spoilers and this data is close enough.
A low spoiler makes the car about a second faster than a car with no rear aero.
A tall spoiler is about a second faster than a low spoiler.
An active spoiler is .28 seconds faster than a tall spoiler.
If you read my previous posts on 3D wings, you’ll know that a 3D wing designed for the Miata’s roofline shape is marginally better than a 2D wing. I’ve included the 3D wing data and a car with no rear aero in the summary data below.
Occam's Racer 