Pushing the Pause Button

I started this website about a year ago with some ideas about testing Miata aerodynamics at Watkins Glen. Through those tests and other research, I feel like I’ve made some decent contributions to the Miataverse. It’s been a fun project, but time consuming and expensive. I was hoping Miata enthusiasts might kick back some my way via PayPal, but only one person has ever donated to the cause.

I’ve had a recent change of fortune, well, more of a reversal of fortune, and I’m now pouring myself into a new venture that will take a lot of time and money. For however long this takes, I have to push the pause button on Occam’s Racer, and get on with the business of starting a business. Unfortunately this new venture has nothing to do with Miatas, cars, or racing. I’m developing a mobile app, and if this is successful, I’ll make it back to my side project with more time and money.

Fitting a Miata to the Aerodynamic Template

There’s a nerdy site and forum called Ecomodder. Most of the site is focused on fuel economy, but some of it can be applied more appropriately to racing. In this post I’ll see how we can apply Ecomodder’s aerodynamic template tool to a Miata.

Aerodynamic template

The aerodynamic template refers to the shape of a car that has the lowest possible drag. It’s basically a tear-drop shape on wheels and looks like this.

Aerodynamic template of the ideal low-drag shape.

The Ecomodder site has an online tool that allows you to superimpose the aerodynamic template over a picture of your car. I’ll do this with a NB Miata using a simple line drawing I found on Google images.

NB line drawing is easy to work with.

I’ll superimpose the aerodynamic template over the car, resizing one or the other so that they fit. The zero mark on the template should line up with the highest part of the roof, which I’m putting in the middle of the door handle.

Aerodynamic template superimposed.

It isn’t necessary to extend the tail to a point. Wunibald Kamm found that cutting off the tail resulted in minimal increase in drag, because the wake region converges to mimic the effect of a fully tapered tail. The so-called Kammback shape is quite efficient at 50% of the cross sectional area, which in this case is the second vertical line past the rear bumper in the picture above. That’s way the heck back there!

A more realistic stopping point is at the end of the trunk, which has the roof at an angle of about 14 degrees. At that length, the roof is still quite flat, and has a shape like a Honda CR-X, CR-Z, or a Hyundai Veloster. And like a lot of SUVs, damnit.

Backlight angle

Most cars these days have rooflines that slope gradually, just like the aerodynamic template, but if you look at older cars, the roofs are often flat, and the rear window comes back at a fixed angle. The backlight angle refers to the slop of the rear canopy, which is often the rear window. The ideal angle is around 15 degrees. It’s not intuitive, but the worst angle is 25-35 degrees. Guess what a Miata’s backlight angle is?

Drag vs backlight angle, 25-35 degrees is the worst.

If you extended the rear window of a Miata to the trunk lid, this would make about a 20-degree angle. This isn’t ideal, but still a lot better than an OEM hard top. Adding a spoiler would be an easy way effectively achieve a better backlight angle.

Image result for miata fastback diy
A pragmatic way to make a fastback

Boat tailing the sides

So far I’ve only been considering the two-dimensional side view, but the aerodynamic template is a 3D shape that tapers on the sides as well. The side taper is referred to as “boat tailing”.

Miata rear end tapers nicely.

You can see that the Miata rear end fits pretty closely to the aero template. Extending the length of the rear quarter panels to the full length of the car (even with the rear bumper) would reduce drag. Although it wouldn’t be necessary to go any further than that. (Note that the end of the bumper is right at the 50% line.)

Streamlining the canopy

The Miata canopy is wide and short, and to reduce drag you need to make it longer. In other words, a fastback. If you’re thinking about building one, bring the sides of the fastback all the way to the end of the trunk lid and you’re at about the right angle. You’d have to figure out a way to relocate the fuel filler, as the fastback goes right over the top of it. But you would save some weight by getting rid of the trunk lid.

Boat-tailing the canopy into a fastback.

My fastback is considerably narrower in the hips, and this allows a more efficient rear taper. This wouldn’t work well on a street car (it creates big gaps behind the windows where water would get in), but a fastback built like this would have less drag, and uses the existing gas cap location.

Diffuser

The final piece of the puzzle is the air going underneath the car. You’ll see the aero template shows a 10-degree diffuser. I’m not sure why this is a fixed angle, I’d imagine a continuous curve would be better.

I had to shrink the aero template to fit the diffuser under the rear bumper, and so this is no longer the ideal shape for the roofline, as it’s too short and the angles are thus too steep.

10-degree diffuser

Ecomod all the things

I also race 24 Hours of Lemons with The Awkward Corner, in a Honda Odyssey minivan. It’s had a few different themes, but if it were my car, the next theme would be a gigantic Honda CRX, following the lines of the aero template.

You can reverse the template and outline color.

I race my brother Ian’s Yaris from time to time. I drew a version of his car with a really long tail that was inspired by the aero template and Porsche 930.

Yaris long-tail

Ian also used to track a BMW E30, which is now with WinSome Racing. I’ve cropped the template to show what it would look like as a shooting brake.

Sebring Race Report

My wife’s parents live in Florida, and we visit them every winter. She has two sets of parents, so we usually stay a couple weeks. I go a little stir crazy with all the down time, and so that’s why this blog post is unusually long. Two weeks away from home also leaves me searching for things to do.

Last year I chartered a boat and went spearfishing. Freediving alone in the ocean is both calming and thrilling. Calming because of the motion of the ocean, the silence, and deep breathing. It’s a kind of mediation I suppose. It’s also thrilling because sharks, big fish, low visibility, and the combination of the them. I had a few opportunities, but I was diving like shit and didn’t spear any fish.

I also went on a wild boar hunt. I put an arrow into a decent hog, but it escaped into the palmettos. In the end I had to enlist the help of a dog, and finish the pig with a knife. Good eating, and a fine winter break.

This year I looked around for something else to do and saw there was a Champcar race at Sebring the weekend after Xmas. My Florida geography isn’t great, so I had to look up Sebring. Oh damn, it’s only 53 miles away from Winter Haven, perfect!

I put a post on the Champcar forum page and got a couple interesting offers from professionally run organizations with arrive-and-drive pricing around $2500. This includes registration, all consumables, and catering. Well shit, at that price, it had better. But I figured this was a rare opportunity to race a bucket-list track, so I should do it.

The first team to contact me runs an E36, and that’s certainly appealing. Rear-wheel drive and a stick shift are table stakes in my game, and BMW handling certainly sweetens the pot. It was a strong possibility.

The second team, RYSA Racing, has a Miata with no windshield. Hurm…. I had previously corresponded with them about aerodynamics on their car, and they seemed like great guys. But the no-windshield thing was a bit concerning. Anyway, I liked ’em, and I know the platform, and I had another idea that would make it even more interesting.

I said that I could bring my wing and other aero parts with me. And then we could do a really neat article on before and after. Meaning, we’d run the car as it normally is on Saturday, and then overnight attach a splitter and wing for Sunday. That would be a cool back-to-back test, and even if not 100% scientific, it would make a great article. They agreed. Cool!

But then I got an offer to drive a first generation MR2. Fawk. My first race car was a MR2 Mk1, or AW11 to the enthusiast. We built a boat around ours, got a Lemons trophy for it, and later a neat writeup.

The M-Ark-2

We swapped in a Silvertop from Japan trying to go faster and cure engine problems, which it did and didn’t. We made it into a Lamborarri and got on a Car and Driver “Best Of” list.

Same MR2, Silvertop, new theme

I wanted to race the RYSA Miata, and write a blog post on comparative aerodynamics, Also I instantly liked the team owner Rudy, and I know we could be fast friends. I felt like a total dick letting him down.

Because when it comes to AW11s, I have a nostalgic streak as wide as Sebring’s front straight. My rose-tinted glasses are at 5%. As such I’m blind to all the troubles that led us to giving the car away rather than race it again.

So as much as I would like to end 2019 writing an article on Miata aerodynamics, I’m going to be completely selfish and drive Team Carma’s MR2. And here’s the other thing, the whole weekend for $500.

Sebring International Raceway

Sebring is a bucket-list track for a lot of people. Not only because of its storied history, but because it’s challenging. The pavement is bumpy, changes regularly between concrete and asphalt, and the track is long and fast. There isn’t any elevation to speak of, but it doesn’t need any more character than it has.

I wasn’t going to just show up and drive, I did my homework. I read every online track guide I could find, watched youtube videos, and most importantly, watched the Speed Secrets “Virtual Track Walk”. The track walk is over three hours of content and worth the price. I was an idiot and didn’t get this until two days before the event, and I really should have done this first, it would have helped me on the simulator.

That was the other vital piece of homework I did, sim racing in Assetto Corsa. My brother Ian hooked me up with a sweet computer, wheel and pedals. The rest of my “sim rig” is decidedly get-tow, with a tiny monitor and a bean-bag chair stuffed under a basement staircase. It’s a lot like Harry Potter’s bedroom without a door or heat.

At first I used a stock Miata on Street 90s tires and my best time was 2:59. I’m not bragging, I’m saying that I suck at sim racing. I can’t drive this car at the limit, and I spin out all the time. I then tried the ND Miata, and I could at least drive that one without spinning, and did like a 2:42. And then I tried the ND Cup car and I recall doing 2:35 or maybe even a 2:32. You guys are like, I can do a 2:27 in that car! Yeah, I’m not a sim racer. Yet.

Here’s what I learned. Turn 1 is probably my biggest problem, and that’s true at most tracks. It’s got to be psychological. I can’t tell where to turn in, or how much speed to carry, and I often wind up mowing grass.

Otherwise I’m generally pretty good in the tight esses and 90-degree bends, so the rest of the track flows alright for me. But Turn 16 is another one where I either overcook it, or leave too much on the exit. And the final corner is a mystery of braking and turn-in points, but it seems you can make some adjustments mid-corner. But this area is riddled with bumps, and the reality may be something else altogether.

Team Carma

It’s a good team name if you have an MR2. What goes around comes around. As in the back end coming around! And the fact that team owner Kevin swapped in a heavier and more powerful 3-liter engine… swapping ends is more likely.

Kevin raced SCCA many years ago, and pressed pause to raise a family. The past five years he’s been racing with Champcar. Over that time, his car has evolved. Like us, he got tired of being abused by the 4AGE, but rather than give his car away, he swapped in a V6 engine from a Camry. These typically put out 190-ish hp, but Kevin says this one has 220 hp. He had to cut up the engine compartment to make it fit, but it’s in there.

A 60-degree V6 will fit with some cutting.

At first Kevin used a stock transmission, but only two bolts on the bell housing lined up, and this required some custom fitting and didn’t last long. This will be the first race on a new manual transmission from a ES300, which are as rare as hen’s teeth. The new tranny required custom axles. If you know MR2s, then you know the axles are one of the weak points. Now imagine putting double the horsepower through them. But I’m getting ahead of myself.

Besides me and Kevin, there are two other drivers, Neil and Kevin #2. Neither has any experience at Sebring. Neil has a lot of short track experience, meaning a 1/2-mile oval. So he’s never raced on a track that has both left and right turns. Sebring has a lot of right turns.

Kevin #2 has no wheel-to-wheel experience, but he did the Lemons Rally to Key West in a Miata kart. He even dressed up as Super Mario. No shit, he’s that guy.

Image result for lemons rally key west mario kart
Teammates with this guy. Cool!

Friday

I arrived on Friday evening and looked over the car. Let’s start with the aero, of course.

The aero package starts with a short airdam and splitter made out of aluminum. It extends to the front axle underneath, but the business end is only a couple inches long. The ends turn up and aim at the exposed tires, which is not so good. In all, the splitter probably helps, but these cars typically need more downforce at the rear than the front anyway.

Airdam and splitter. Love the tow chain, I’ll use it.

The rear aero is the stock spoiler moved back a few inches, the Plumley mod, as it’s called. In addition, Kevin made the entire trunk adjustable, so he can increase the height and angle to four positions. It’s a simple DIY solution and I love it.

Simple adjustable spoiler. Notice license plate, this is street legal!

Before I move onto the rest of the car, I’ll note that I saw more cars without rear windows than with. This is an aerodynamic challenge for anyone using a wing, but the Champcar rules specify no rear glass. So for teams that don’t want to shell out for Lexan windows and the required aluminum supports, they just remove all the rear glass.

Back to the MR2. I noticed the tires were staggered, with 205/40-17 on the front and 225/17 on the rear. The rear tires are the largest diameter that will fit, which Kevin chose for taller gearing. I would have fit 15″ wheels, but it’s not up to me. The tires are Falken Azenis 615k+, which I’m familiar with. Kevin starts these at 30 psi, but doesn’t really adjust them. Which is a no-nonsense approach, but I’m seeing the start of a pattern.

I asked about the brake pads, and Kevin said he didn’t know. Are they race pads? No. Hmmm. I’ve never raced on “I don’t know” pads, so this should be interesting. The shocks also feel a bit soft, and I confirm they are simply cut springs. There are a lot of small details like that, which add up to a car that is, let’s say, not exactly race spec. But it is what it is, and it looks fun.

Ok then. The team owner has some interesting ideas on car setup. The other drivers are inexperienced, and both of them are scheduled to drive before I do. The forecast is for rain, and this is a treacherous track in the rain. At this point I’m certain the car wont last the weekend, and the over-under on me driving at all is about 50/50. Just the same, I’m feeling right at home with this car and these guys. Fuckin bring it.

Saturday

The race started with a bang. Or rather, two bangs. There are two pairs of black rubber stripes on the front straight, which is where the drag racers launch. This area has been treated with some kind of chemical for increased traction, which works in the dry, but has the exact opposite effect in the wet. In addition, the paint on the start/finish line is icy when wet. And it’s pouring. If you accelerate or change direction over these two areas, the car slides.

Green flag. Bang! Two cars hit the side walls before start/finish of the first lap. A few laps later another car would join them. And then another. And then another. The Champcar staff had to call an emergency driver’s meeting and tell all of us what we already knew: don’t accelerate or change direction on the black stripes or the start/finish line.

To Sebring: Clean that drag-racing shit off your front straight, it’s downright dangerous. Or better yet, don’t treat the track! Drag racing is about comparative times, it doesn’t matter what the surface is. Yes, we were told about this hazard in the driver’s meeting, but it’s within your power to make your track safer, and you made the track more dangerous. Even your safety car had problems staying on track!

We didn’t hit any walls, but this is a rookie team, and we made other rookie mistakes. Some examples of this:

  • Kevin #2 had the least experience, so he went first. We were gridded in 7th place, but because of an ill-fitting Hans anchor, he left in last place.
  • The radios gave us fits, caused an unscheduled pit stop, and never worked well.
  • The shifter cables got disconnected by getting caught on the driver’s sleeve. This resulted in another pit stop.
  • At the end of Neil’s stint, Kevin sent him out for three more laps. He interpreted this literally, and so when the entire track went full-course yellow on his out lap, he stayed out there during the entire FCY laps rather than use this for the pit window.
  • You only break parts you don’t bring. But I’m jumping ahead.

Despite these things, I was really proud of Kevin #2 and Neil. They’d never been to the Sebring before, were racing wheel-to-wheel in dangerous conditions, and brought the car back in one piece. They had their moments and saved them, and set some decent lap times in the process. Nice job.

I got in the car around 12:30, in some of the better weather we’d seen. I even turned off the windshield wipers for a couple laps. Despite the dry-ish track, I never got any heat into the tires because I couldn’t push the car. It just didn’t handle. At least not how I remember my MR2 handling.

I’d turn the steering wheel, the front tires would kind of take a set, and then the back end would come around, like there was a hinge in the middle that had to catch up with the front. The brakes didn’t inspire confidence, but at least they were water cooled. The suspension was way too soft, even in the rain. After a couple missed attempts at 2nd gear, I didn’t go below 3rd.

The engine, tho. The engine. More weight over the rear wheels, more power to them, and you can accelerate like crazy. The engine signs off at 5500 rpm, but so what. Short shift and pin it. I passed people on power, which never happens in a Miata.

It took a while to get accustomed to the point-and-shoot nature of the car, but I was getting there. And then on the entry to T5 I heard a clunk from what felt like the right rear wheel, and the car stepped out a bit more than usual, as if it had a second hinge. I backed off until I’d exited T6, gassed it, and then right in the middle of the back straight, suddenly the car popped out of gear and I had no power. I rolled to the inside of T7 and waited for a tow.

Back in the pits we found the problem, a broken RR CV joint. The axles on this car are custom made for the transmission, and Kevin didn’t have any spares on hand. We went to a local parts shop and got a standard MR2 axle, but we couldn’t fit it and our weekend was over.

The bearings are somewhere between T6 and T7.

Further inspection of the car showed a RF wheel bearing with a lot of play, and the entire wheel was moving 1/2″. I was on my way to a parts store 90 minutes away when they discovered that it was simply the nut backing off. Also the front sway bar was disconnected. Sebring’s bumpy surface will rattle apart anything that isn’t loctited or wired down, and these problems were probably victims of the track.

These two problems help explain the funky handling, and why I can put on my rose-tinted glasses back on and still call the AW11 the best handling car I’ve driven. Just not this one.

Sour grapes

This wasn’t my worst racing weekend. One time I flew out to California and the car broke on the first stint, and I never got to drive it. Another time I came together with an E30 at Watkins Glen and ruined both our weekends. Measured against these, this weekend wasn’t so bad.

I paid $500 for 12.5 laps. This works out to about $40 per lap, or $720 per hour. However, I got to race wheel-to-wheel at high speed, on an iconic track, in a nostalgic car. If I do the math, that’s less expensive than autocross, and a hell of a lot more fun than dodging cones in a parking lot. When things go badly, it feels better to point the finger at other people. So there I go bashing autocross again. I still don’t fucking get it.

Swedish Simulations

Every year my sister Mia gives me Swedish Fish in my Christmas stocking. This year I’m in Florida (I’ll be racing Sebring next week), and I won’t get any candy. Instead of getting something Swedish, I’ll give something.

The other day, Torbjörn Linderson (I’ll call him Torb hereafter), from Sweden, asked a question on the Miata Race Prep group about aero modifications vs weight and should he do them. The question started vague, and with limited information I said do the wing, based on the fact that in every racing simulation I’ve run, a car with a wing beats a car without a wing. Another person with more knowledge and less science said that a low-drag wing (like my 9LR) doesn’t do anything until 80-90 mph, and that he wouldn’t use one.

That’s an interesting statement, and it begs the question, at what speed does aero start working? To see if aero helps at a lower speeds, I’ll do a quick simulation in OptimumLap. Using a stock Miata (with windows open) and some round numbers: .50 Cd, -.50 Cl, 2450 lbs, 1.1g static grip. I’ll run this car through a low-speed corner (T1 Pineview) and it goes 66.25 mph. Now I’ll use a Miata with airdam (no splitter) and 9LR wing for .05 Cd and +0.68 Cl (OptimumLap reverses the lift number). Now the car goes through the corner at 66.80 mph, a difference of .55 mph.

You might be thinking that half of a mile-per-hour is nothing, but it works out to 104.58% more grip, which is not nothing. But I’m citing a car modified with airdam and wing, not just simply the addition of a wing and no front aero. But at least we answered the question of, is aero useful at less than 80 mph, and the answer is yes.

Torb gave us more details on his car and the rules he races under, and that made things even more interesting. Blog post interesting.

The rules and the car

Torb races under the Roadsport C rules, which are a bit like NASA ST/TT rules, using kgs/hp with allowances for minor tuning. Without getting too deep in the details, his car would be at the class limit with 147 hp and 2367 lbs. That’s a pretty decent Miata, right between NASA TT5 and TT6.

The rules allow aero mods that don’t protrude from the body as seen from above. This is a lot of leeway, and would allow him to use an airdam, or an OEM-style front end with a splitter, as long as the splitter doesn’t protrude beyond the front bumper. He can also use a spoiler and flat bottom for free. So right away I’m thinking this: build a Supermiata with a flat floor! I’m a big fan of spoilers myself, and that may yet be the conclusion, but let’s move on.

The rules don’t allow him to change the roofline shape, and so a chop top or fastback are not allowed. But he could remove the rear window from a OEM hardtop and get the slightly better lift value of the chop top.

But Torb is interested in a wing. The wing needs to be mounted within the shape of the body as seen from the top, which is about 60″ (same as my wing). The wing needs to be 2″ below the roofline, and I can’t simulate that and will just use the roofline. The end plates can measure up to 10×10 square, which is within an inch of mine. The major problem with a wing is that it incurs a a 5% weight penalty.

As the car sits, Torb can just squeeze below min weight limit. However, it would be really easy to add weight. Starting with a 40-lb lead-acid battery instead of the 2-lb race battery he has now. The wing and stanchions are about 20 lbs, and a flat floor made out of metal could easily bring the weight up, and ballast would do the rest.

Front end options

Torb needs to keep the front-end aero within the lines of the stock bodywork, when viewed from above. In addition, if he adds rear downforce, he needs to balance that in front. The two obvious front-end options are a vertical airdam, and an OEM bumper with a splitter that extends only to the front bumper.

That’s exactly how my car is currently set up, see the pic below. In addition, I have a splitter extension I can add to this, it bolts on underneath. This can be easily adjusted so that the length is flush with the front bumper, when viewed from above, or to any length I want.

OEM front end with undertray acting as a short splitter. Splitter extension not shown.

Such a front end would have more drag, but also more downforce, than an airdam. I haven’t tested this myself, but CFD from Hancha/Velox came to this conclusion. Compared to the airdam, they said it would have .01 more drag and .07 more downforce. These seem like reasonable numbers, I’l use them.

Swedish tracks

Torb sent me details on the three tracks he races on. If you follow the links below, you’ll see different cars with lap times which lists the power/weight ratio of the car, and what kind of tires the car is using. Hallelujah for good data!

  • Kinnekulle Ring is a short 1.28 miles, lots of flowing corners, very little braking. The best Miata lap on slicks is just under a minute. At the other end of the spectrum, a 1990 Miata with 19 lbs/hp lapped at 1:06.17, which is another useful data point. So far this is looking a bit like Lime Rock, which is slightly longer (1.47 miles) and faster.
  • Mantorp Park is 1.93 miles, with a long uphill straight. Watch a Civic K20 do this in 1:26.55. It’s a bit like Thunderbolt without the chicanes, but the speeds look more like Summit Point.
  • Gelleråsen Arena is 1.57 miles and Torb does around a 1:17 lap. The track has three 2nd-gear corners where aero wouldn’t do much, but it starts end ends with a complex of of 3rd gear corners where aero would help. Waterford Hills is 1.4 miles and tighter, but this is probably the closest approximation.

Car builds and simulations

There are four configurations worth testing here. I’ll name them so it’s easy to follow.

  1. OEM – Open windows destroy a Miata’s drag and lift numbers. I’ll be kind and call this Cd .50 and Cl -.50, 147 hp, 2367 lbs.
  2. SuperM – I don’t have real numbers for the Supermiata formula of an airdam and spoiler. I do have comparative data from my car, plus drag and lift numbers from cars that have similar aero. I’ll call this Cd .50, Cl .40. 147 hp, 2367 lbs.
  3. Sp-SM – As above, but with an OEM front end and splitter (not the airdam). Cd .51, Cl .47. 147 hp, 2367 lbs.
  4. Ad-Wing – This version uses an airdam (no splitter) and wing. This is actual data from my car with OEM hard top. Cd .49, Cl .68, 147 hp, 2485 lbs. This version should also use a flat floor, since Torb needs to add weight anyway, but I don’t know what that would do for drag and lift, so I won’t factor that in.
  5. Sp-Wing – As above, but swap the airdam for an OEM front end with a splitter. Cd .50, Cl .75. 147 hp, 2485 lbs.

In all cases I’ll use 1.3g grip. Torb sees spikes higher than that, and the class limit is 1.4g, but in steady cornering 1.3g seems a good value.

At Lime Rock (which I’m using to simulate Kinnekulle), the average speed is around 90 mph, and you can see that the airdam-wing setup is almost a half second faster than the airdam-spoiler version. In addition, the OEM front end with a splitter is another .1 seconds faster.

It’s not really worth mentioning stock aero, because it sucks. All of the aero options beat the OEM bodywork by over two seconds.

OEMSuperMSp-SMAD-WingSp-Wing
62.3960.2060.0859.7459.64
Kinnekulle (Lime Rock)

At a lower speed track, like Waterford (which I’m using to represent Gelleråsen) average speeds are around 70 mph. But it’s pretty much the same relationship with the wing coming out on top, despite the extra weight. The gap isn’t as great, however.

OEMSuperMSp-SMAD-WingSp-Wing
76.7574.9074.7874.6174.50
Gelleråsen (Waterford)

Another thing worth noting is that on the cars with a spoiler, the OEM front with the non-protruding splitter is .12 seconds faster than the one with the airdam. It’s weird that it’s the same time difference at both tracks, but the airdam is always slower. I’m not sure this would bear out in the real world, though.

Screen shot of some of the data.

Oh shit, OL has Swedish tracks

I went looking for more track maps and OptimumLap has seven Swedish tracks! Among them is Torb’s home track, Linköping, and his favorite track, Kinnekulle Ring. I re-ran the simulations again, and while the results were the same for Kinnekulle Ring, at Linköping the wing versions did not win!

OEMSuperMSp-SMAD-WingSp-Wing
65.1364.1164.0664.1764.12
A spoiler and less weight beats a wing by .06 at Linköping.

Conclusions

In all but one of the scenarios, the wing wins. But that’s making the assumption that the wing is not affected by mounting it 2″ below the roofline, and it might be. And even though this is a simulation based on scientifically acquired data, it is a simulation. YMMV.

If this was my car, I might choose an adjustable spoiler, primarily because I’m lazy. The car is already at the class limit, and a spoiler is less work. The wing is more expensive, and would require modifying the car. Although that would provide an opportunity to use a flat floor, and add ballast where I wanted it. If Torb adds a flat floor to the spoiler version, he needs to remove weight to offset that. If that proves difficult, the wing is the obvious choice.

Torb had also asked about using a hardtop without a rear window, and if you’ve read my results on that, the answer is yes if you’re not using a wing, and no if you are using a wing. I don’t know what the answer is with a spoiler, but it would be fun to A/B test it.

Regardless of what happens at the back, I would use an OEM front end with an adjustable splitter and vertical end plates, rather than an airdam. While the airdam has slightly less drag, the adjustability and extra downforce could be more useful. It’s also easier to load on a trailer with less overhang. And let’s face it, everyone can use .12 seconds.

P71 Interceptor Cup

The other day we had a flurry of activity in our Unofficial Pineview Run Fan Group. It started with a brag about lap times, which got to guys (ahem) measuring themselves without anyone having a ruler.

And then my teammate Evan suggested we should have such a ruler, or call it a village bicycle. With a shared vehicle, everyone could compare lap times on a level playing field. Well that makes a whole lot of sense, what would it take?

We discussed different cars for this application. For the first time, Miata wasn’t the answer, because a lot of people don’t fit in one. A BRZ/FRS is better, but initially more expensive. BMW E46 is a great platform at a reasonable price, but maintenance and parts costs are higher. And then my teammate Pat says what about an old cop car?

P71 Interceptor

There are a lot of different models of cop car, but what Pat and probably anyone else is thinking when you say “old cop car” is a 1998-2009 Ford Crown Victoria Police Interceptor, often called by its code name, P71. Part of Pat’s reasoning was that most people wouldn’t be familiar with the platform (except the back seat), and that starts people on even ground. In addition, P71s are cheap to purchase and fix, have rear wheel drive with decent power, come with heavy-duty parts more suitable to track life, and will fit just about any driver.

Image result for p71 interceptor race car
Ford Crown Victoria Police Interceptor (P71). Looks like Pineview. Isn’t.

I thought about it some more and there are other virtues to the P71. Being heavy, it’s less sensitive to driver weight, and so correcting for that will be easier. It’s got rear-wheel drive with some have an open diff, making traction sensing an important skill. It’s got ABS so we don’t flat spot tires. Heck, even the auto trans is a virtue, maybe get some millennials on track!

If I can’t convince you, check out the following videos which come to the same conclusion in a very different way.

So the car has a lot of merit, and on top of that, there’s the whole police angle. Pineview Run does police training at their facility, and so we might even get the officers to run laps – get a little cops and robbers thing going. Or fan the fires of inter-department police rivalry – which highway patrol has the fastest driver? Or, settle the argument on old age and treachery vs youth and skill, pitting retired cops vs rookies. Or, for manufacturers, benchmark the latest cop cars vs the P71s Interceptor. Yeah, this police car thing has a lot going for it.

But the P71 is not a “county club car”. It’s not selling the image of an exclusive and high-end motorsports club. But IMHO, what the club needs right now is more people coming to the track and driving it, not judging it from a distance. The P71 contest could be a tasty carrot, something that brings people to the track and facility. At this point in time, there is no such thing as bad publicity.

PVP71 Competition format

The Pineview Run P71 Interceptor Cup (PVP71 for short) competition would run all year long. Anyone can rent the car for a regular 15-minute session, start the Aim Solo, and lay down some laps. At the end of the year, the top finishers get some kind of prize, maybe a cash reward, their name on a perpetual trophy, that kind of thing.

To make the P71 competition fair, we’d need tires that don’t change much over their lifespan, and stay consistent over different temperatures. Hankook RS4s will do that. We have data from our last race that shows time of day had no statistical impact on lap time. We used old tires on Saturday, and brand new on Sunday, and so tread depth, heat cycles, and track temperature seem to have a minor effect on these tires.

Stock tire size is 235/55-17. The RS4s are only available in 235/45-17, but maybe that’s not an issue. If we stick to the stock size, the most common cop tire is Goodyear Eagle RS-A (260 TW all-season). Firehawk Indy 500 and Dunlop DZ102 are also available in that size, and I’ve heard similar comments about the DZ102’s indifference and lifespan, but have no data on that.

We also need a way to adjust ballast between drivers, but that should be easy with some removable ballast weights and varying fuel loads. In the future we may be able to have a correction factor for driver and fuel weight, eliminating the need for ballast. So we should keep a detailed log of everything, including air temperature, track temperature, wind speed, and other variables, and correct for those as well.

Special events

Aside from the regular on-demand rentals, I can imagine a lot of special events, here are some ideas.

  • We’d need an initial weekend event to settle on a standard tire pressure, adjust suspension, figure out ballast, and other baseline tuning and setup.
  • We could have a P71 Open Test Day, where many people get to drive the car for shorter sessions, in a non-competitive environment. Pineview is often empty when it’s raining, so this could be a good opportunity.
  • It would be great to get some police officers at the track with civilians and do a meet and greet. Try out some of the newer cop cars against the P71. Shoot some guns. No really, because Pineview is also a sportsman’s club, and shooting is a part of that. We could even do a shootout with the cops (competing on paper targets, of course).

Simulated lap times

If you thought I was going to do a blog post without simulating lap times, you haven’t been reading my blog for very long. Here are some optimum laps based on 236 whp, Cd 0.46, Cl 0.40, at 3900 lbs and 4100 lbs. Take this with a big grain of salt.

Tire 3900 lbs 4100 lbs
All season1:21.091:21.26
Older summer tire (DZ102)1:19.601:19.78
Newer summer tire (Indy 500)1:18.211:18.38
200 TW enduro tire (RS4)1:16.911:17.08

If those times work out, it’s faster than my Miata. It burns a bit to write that. Nah, that can’t be right. Can it?

Let’s do this

There are three main hurdles to get over.

  1. Convince Pineview (mostly Todd) that the P71 fits into Pineview’s vision. [updated] We have the go-ahead!
  2. Someone (me, probably) has to buy the car, prep it for track duty, and maintain it throughout the season.
  3. We need a pricing model that is cheap, but also pays for the car and track time fairly.

To point number 2, my instinct says to buy the car myself and it’ll all work out. I don’t have the time or inclination to prep it for track duty and do regular maintenance, but if this is a community effort, then people will help. If you build it, they will come.

Point number 3 will take some math. Logistically, the price of the car, plus tires, brake pads, fluid changes, a better seat, and other necessities is probably $3400. If we take $17 per rental and apply it to the car, we need 200 rentals to pay for it. That equals 50 hours of track time, which is another set of tires, brake pads, fluid changes, etc. Consumables will run about $70-80 per hour, so around $18 per 15-minute rental.

If running cost is $18 and car payment is $17, then the minimum price for Pineview members, annual pass holders, and people using a track pass is $35 per 15-minute session.

For non-members doing an arrive-and-drive, pricing would have to include track access, which is around $50 per 15-min session (based on getting six 15-minute sessions and a $300 track pass). But if we base it on the current sale price of $209, that’s $35 per 15-minute session. In which case the price is $70 for non-members.

The $35/$70 pricing is as low as we can do it, and the pricing doesn’t include anything towards awards, cash prizes, etc. We’d have to add $5 to each session if we want those things.

Eventually the car should pay for itself (or rather pay me back), and then it can start paying for its upgrades. And by upgrades I mean in-car video, live timing, four on-track cameras to capture the action, etc. Eventually we live stream everything, so that people sitting at home can watch you set a new lap record. Or go four off.

I’m really liking this P71 Interceptor Cup concept . Who’s with me?

New Time Trial Rules

Last year’s Pineview Challenge Cup had a unique (and flawed) set of rules, using only tire treadwear to class cars. The “Race” class was any tire under 200 UTQG, the “Track” class was for any 200, and the “Street” class was for 300+. On the plus side, we had no rules lawyering or protests throughout the season, and it was easy to manage three classes. On the downside, the rules didn’t take into account power, weight, tire width, or the fact that there’s a great deal of variation within each tire class. In the end, the racing wasn’t always close.

We need a better set of rules for 2020, and so I took it upon myself to do some research. First, I put all of the lap times from the Pineview races into a spreadsheet, and noticed they fell into four groups. I figured that whatever rules we come up with, they should place people into four groups.

  • Under 1:14 – Just three people were in this group.
  • 1:14-1:17.2 – Fast cars and fast drivers, but only five people in this group.
  • 1:17.8-1:19.7 – Fourteen people, diverse cars and drivers, close racing.
  • 1:20.1+ Six people, some newcomers, a wider spread of times.

I then ran hundreds of simulations in OptimumLap at Pineview Run, using different cars, power/weight ratios, tire grip, and aero. I put all of them into a spreadsheet, and analyzed the data. Let’s take a look at what I did for a Miata with various power and grip values.

MiataHP  (lbs/hp)1.0g 1.1g 1.2g 1.3g 1.4g
Stock NA8 100  (24.5)82.3479.1376.3773.8871.65
Spec Miata125  (19.6)81.2577.9875.1472.6470.46
K-swap200 (12.5)79.6076.1473.2070.6468.42
Turbo, Rotrex265 (9.2)79.3975.6972.5169.7767.42

You can see that tire grip is the most important factor. For example, a Spec Miata on 1.3g tires will beat a K-swapped Miata on 1.2g tires. The lbs/hp ratio is also very important, especially as you add more grip. But on shitty 1.0g tires, power gives diminishing returns, and cars with better than a 12:1 ratio are pretty evenly matched.

Existing time trial rules

With this data on hand, I then reviewed the rules of nine time trial series to see if we could leverage them, and learn how others are doing it. Here’s a quick synopsis.

  • NASA PT/TT – The old NASA rules listed and ranked every car and trim level, and everything you might do to it. It seemed like a fair system, especially how they ranked tire compounds and width. But they abandoned it for a reason.
  • NASA ST/TT – The newer NASA TT rules are much easier, and seem very fair, based mostly on lbs/hp. My main gripes are 1) everyone needs to dyno their car on a Dynjojet. 2) Many common modifications are not allowed. Why not just make them a point value instead of making them illegal? 3) The new tire system favors race tires, not tire choice.
  • SCCA Autocross – 36 classes and a 387-page rule book?! I didn’t wade into this tome; this is the exact opposite of what I want to do.
  • SCCA Time Trials – I’ve got some issues with how cars are classed. In the “Sport” category, all Miatas from 1990-2015 are in the same class. If you know Miatas, you know how stupid that is. If you’re going to do that, you may as well put the BRZ/FRS in the same category as a 1990 Miata. Which they fucking did. I should have stopped there, but kept reading and found that in the “Tuner” category, they put E30s in with S2000s and ND2 Miatas. Ha ha ha ha. Anyway, there are five main categories with subdivisions that make 20 classes. The stock-ish categories are based on a car list, while in the modified categories, cars are classed by displacement divided by weight (as if displacement is a good indicator of power). These are new rules and maybe they need a few seasons to refine them, but the rules look unbalanced and unfinished.
  • EMRA – Kudos to them for making a 12-page rulebook! As such, it’s sparse and open to interpretation. There are ten classes based on a car list. You bump up a category based on modifications, but there’s not a lot of balance to the mods. The only thing they say about tires is that they must be DOT. There’s a world of difference in there, I guess everyone shows up on A7s?
  • Porsche – PCA has a great system of ranking their cars and various points for modifications. It looks very fair and complete. But they have only one brand of car, and they split them into different 28 classes. We can’t afford to give out that many trophies or manage that many classes. BTW, if you ever wondered about the comparative performance of different Porsches, look at the point values, it’s great data.
  • Speed SF – The classing system is calculated from a relatively simple worksheet that puts you into one of six classes based on a list of cars and modifications. The classing rules are simple, and because of that, there are going to be inequalities within the classes. Tires are easy: everyone is assumed to be on 100 TW or higher, and you take a slight penalty for using race tires. I like this system for a lot of reasons.
  • COM – Corvette Owners of Massachusetts have the best rules I’ve seen. It’s a bit like the old NASA system, and takes into account tire compound, width, and really anything you want to do to your car. This puts you into one of ten classes. The 98-page rulebook is a tad long, but they have a great spreadsheet calculator that makes classing easy.

After all that research, I’ve come to the following conclusions.

  • Creating a fair classing system is difficult, and nobody does it the same.
    • One starting point is to list and rank every car .
    • Another starting point is pounds per horsepower.
  • Tires are a very important factor.
    • Many rules evaluate each tire individually.
    • Tire width is a factor, and often relates to weight.
  • It would be easy to use another club’s rules, but impossible to manage them. Our time trials are run over 2 hours, and we simply can’t have more than 4 classes.
  • I poke fun at some of the rules above, but I applaud any effort to make racing fair and fun. Every system is full of good ideas, this is just a really difficult problem to solve.

Creating new classing rules

So with all of that knowledge, I went about creating new rules. My guiding principles were:

  1. I need to end up with only four main classes. Ideally these should correlate roughly to the lap time groupings observed in the 2019 season.
  2. The classing rules must be fair, and allow people to run what they brung. It should be easy for people racing in other series to cross over.
  3. The rule book should be short and simple.

Pounds per horsepower

I started with pounds per horsepower, because that’s easier than ranking every car in existence. For people who dyno and weigh their car, getting lbs/hp is easy, but most people won’t do that, so the rules allows using factory values.

lbs/hp = (Factory weight + driver weight) / (Factory HP * .83).

Of course people modify their cars for less weight and more power. So they must declare, on their honor, what their modified weight and power are. This is obviously a place someone can cheat. However, I would make the class worksheets public, so anyone obviously cheating would be publicly shamed, a-la Game of Thrones.

For people racing in the NASA TT series, which is based on lbs/hp, they can use their class minimums. Meaning TT6 is calculated at 18:1, TT5 at 14:1, TT3 12:1, and the faster classes at a 10:1 cap.

For other racing series that don’t use lbs/hp, I’m experimenting with some crossover rules. These would let people bring their race car on their spec tire, and fit into a class. But more on that some other time.

Tire grip factor

I used the tire point values from the old NASA series and COM, and then cross listed with recent tire tests, forums, and various web pages to come up with a hierarchical list of tires sorted by grip value.

PtsUTQGTypeExamples
2400+All seasonAny all-season 400+
3300-390Summer -olderYok S.Drive, DZ102, G-force Comp2
4240-380Summer – betterContinental ECS, Michelin PS4S, Bridgestone Potenza S001, Champiro SX2 (260), Toyo T1R, any 240+ not listed
5180-200200 EnduroAccelera 651, Champiro SX2 (200), Dunlop Z2/Z3, Falken Azenis 615K+, Federal RSR, Hankook RS4, Maxxis VR1, Nankang NS2R, Nitto NT05, Toyo R1R, Yokohama AD08R
6120-200Auto crossBridgestone RE71R, BFG Rival 1.5 S, Federal RSRR, Michelin PS Cup 2, Nexen Sur 4G, Yokohama A052, any 120-200 not listed
6100R-CompNT01, RA1, R888R, RC1
740-80R-comp softNankang AR1, Toyo RR. Pirelli Trofeo R, any 60-100 TW not listed
840RaceBFG R1, Goodyear Eagle RS, Hankook Z214 C51/C71, Hoosier R7, SM7, Kumho V710
1040*Race softBFG R1S, Goodyear Eagle RS AC, Hankook  Z214 C91, Hoosier A7, any 40 TW or less, not listed

I then assigned a point value to each tire, so that I could try out different formulas that would make lbs/hp and tire grip meaningful. I tried a few different ways to balance lbs/hp with different tire grip values, and make that correspond to real and simulated lap times, and simultaneously group people into four classes.

In the end, classing is based on a simple formula: FLOOR(Lbs/Hp/Tire). Or in plain english, the weight of the car with driver, divided by the wheel horsepower, divided by tire points, rounded down to a whole number. This usually results in a number 1 through 4. That’s your class.

Low-powered cars on hard tires may evaluate to more than 4, but they still must run in Class 4. We aren’t making a 5th class, there’s just no way to run that many groups in a two-hour session. For the same reason, there’s no Class Zero. So that makes Class 1 basically a no-limits class. Whatever car, on whatever tire, bring it.

Examples

To see how this works, let’s take a look at a Honda S2000. Weighs 2850 lbs with driver, dynoed at 200 hp = 14.3 lbs/hp. Different tires would put this car in a different class.

  • R7: 14.3 / 8 = 1.83, round down. Class 1
  • RE71R: 14.3 / 6 = 2.38, round down. Class 2 
  • ECS: 14.3 / 4 = 3.75, round down. Class 3
  • S.Drive: 14.3 / 3 = 4.76, round down. Class 4

Let’s take a look at a Spec Miata, which would be at the 20:1 lbs/hp cap.

  • Hoosier A7: 20/10 = 2.0. Class 2
  • Toyo RA1: 20/6 = 3.33, round down. Class 3
  • Dunlop Z3, 20/5 = 4.0. Class 4

Or using a car crossing over from NASA TT4, which has a 12 lbs/hp minimum.

  • Hoosier A7: 12/10 = 1.2, round down Class 1.
  • Toyo RA1: 12/6 = 2, Class 2.
  • Michelin PS4S: 12/4 = 3, Class 3.
  • BFG SC2: 12/3 = 4, Class 4.

So that’s how it works, pretty simple. But is it fair? I ran a bunch of simulations using four different cars that I have data for, and the lap times come out pretty close to how I had them grouped.

One thing I found out was that this formula works best for cars in the middle range. Cars with high lbs/hp ratios, like Miatas were going too fast on sticky tires, and so I put a cap on all cars at 20 lbs hp. If your car is slower than that, you still have to use that value. Likewise, high-power cars at the other end of the spectrum were treated unfairly by the classing formula, and so I put a 10 lbs/hp cap on that. So if your car is 6 lbs/hp, it’s classed at 10. With these mins and maxes set, the simulated laps fall very close to reality.

Caveats and final thoughts

The rules are based on real laps and simulated laps at Pineview Run; I don’t know if this system would be fair at any other track, that was never my intention.

I was trying to place people into four groups, and the rules work out for that. If I doubled the number of classes, there would be more equality between cars in the same run group. But it isn’t logistically possible to manage that many classes in a 2-hour evening session.

Here are some final thoughts, in no particular order:

  • This is the first year we’ll try these rules, and we might need a mid-season addendum. This should be pretty easy by changing tire point values, or adding a tire width factor.
  • To keep things simple, I didn’t take tire width into account. But an easy calculation is to take the average tire width, and divide by 245, and multiply that by tire points. This means that every tire under 245 width would get some advantage, and a width over 245 would get some penalty. As an example, a 195 RE71R would be evaluated the same as a 225 RS4. The average tire width could be anything, I’m speculating on 245 because it seems right. This could also go by class, so that Class 4 has a 205 width average, Class 3 has 225, Class 2 has 255, and Class 1 is 275.
  • I’m not stuck on tire point values, or integers. For example, we might find that Z3s and R1Rs should be evaluated at 5.5 points instead of 5. Or that RC1s are really a 7-point tire, not 6. We need real-world data before making any adjustments, tho.
  • I didn’t take into account modifications to suspension, brakes, aero, or really anything else you might do to a car. All of these are important, but not as significant as lbs/hp and tire grip. Not at Pineview, anyway.

We are still working on the final rule set, which includes things like points per race, and how the season points add up to who gets to put their name on the Pineview Challenge Cup. But I thought people would like to see the classing system ahead of time. The first race isn’t until Saturday May 2nd, so there’s plenty of time to break out your calculator and figure out the optimal tire for the class you want to run in. Or if you’re doing it the other way around, figure out how many pounds to remove or horsepower to add, so you can use your favorite tire.

2020 Aero Tests and Projects

I’ve been thinking about what to build and test in 2020. It’s a long winter here in upstate NY, and I’ll have some time on my hands. I just got my barn floor poured with concrete, and now I have 950 square feet to let my imagination run. Here’s a list of what’s on my mind. Leave a comment if there’s something in particular you’re interested in.

  • Underbody aero – Is it worth doing on a Miata?
    • Flat bottom – I’m very curious about this one, not sure if I’ll do this on my race car, street car, or both. I installed a canon subframe brace in my 1.6 specifically so I could hang the flat bottom off it. So… it’s fairly likely this will happen at some point.
    • Side skirts – The race car lost one side skirt spinning out at Mid Ohio. I’ll make new side skirts, which will be wider, and fit next to the pinch welds, reinforcing the jacking points along the entire car.
    • Diffuser – I made a diffuser out of aluminum street signs (I must have been in a Lemons frame of mind), but I haven’t mounted it yet.
  • Misc aero projects – Some projects are partially done, some are just drawings and ideas.
    • DIY fastback kit – I’ve been thinking about building a fastback kit for a Miata. This would be for race cars only. It would be a bunch of parts that can ship flat, and then you assemble it at home, fiberglass the seams, and paint it. My main problem with creating a product is I don’t want to support pain-in-the-ass customers.
    • 3D wing visualizer – This is a series of pivoting airfoils that I can mount on any car, just like a wing. It shows the shape and angle of air where a wing would be mounted. This would be great for setting wing height and angle, and also figuring out what’s the ideal shape of a 3D wing for just about any car. For science!
    • eBay wing 2.0 – Continue modifications to my cheap eBay wing to reduce drag and increase downforce. I’ve already started on this project because it’s a total fucking waste of time and that’s how I prioritize things.
    • End-plate mounted 9LR wing – This would require building new wing stanchions that mount to the rear quarter panels and come up vertically. Think Ferrari F40.
    • Shooting brake – I didn’t finish the shooting brake top I started earlier this year. Theoretically, it could have less drag than my fastback, and better visibility. And it’s unique looking.
    • NASA TTop – The TT6 rules allow convertibles to change the roofline shape, but the roofline must terminate at the front edge of the trunk. I have some ideas on how to build a roof with those limitations, but they are all sort of weird looking, like a Lotus Europa or Porsche 914. But they would have less drag and would work well in conjunction with a rear wing. From a practical standpoint, the trunk would still be functional.
    • Mazda RX500 top – This would be a custom top for 24 hours of Lemons. It’s almost like a station wagon, and would be simple to build.
    • Shark fin soup – Make a LeMans prototype-style top, complete with shark fin. If it works, race it in AER. If it doesn’t, race it in Lemons.
  • Aero+ tests – To do these properly I need to hire Jeremiah again. Without him, it’ll be just Aim Solo data which is a lot less accurate.
    • Underbody aero – Test different combinations of flat bottom, side skirts, and diffuser.
    • Front end aero – I didn’t get to test a stock front end vs R-package lip vs airdam. I have all the parts. I think we all know which is best, but how much better?
    • Low-speed aero – It’s easy for me to test low speed aero at my country club, Pineview Run. I just need to get my shit together, bring all the parts, and do it.
    • Spoilers by the inch – There’s a neat website called Ballistics by the Inch, where they start with a long gun barrel and progressively cut it shorter and record the resulting velocity. My test would be like that, but progressively a taller spoiler and record lap time. What’s the optimum spoiler height?
    • Tires – Pineview is a great place to test tires. I have some ideas in mind, like using one tire, and trying different widths, to see how much just tire width changes things. For example, I could test RS4s in 195, 225, and 245, on 7.5, 8.5 and 9″ wheels, respectively. I’m not sure how useful that is, but I’ve always been curious about this.

What’s on your mind? Leave a comment.