Mid Ohio, Part 3: Race 1

Sonny at the office.

The prep and testing is done. Practice and qualifying sorted. Car and team are as ready as we’re going to get. Just one final detail is our driver order.

AER requires five pit stops over the course of the day, and in a typical 9-hour day, this means each driver gets about 90 minutes of racing. The race was shortened to 8.5 hours, presumably because it’s late in the season, so that was a bit less track time for everyone. But we still needed to do six stints with four drivers, so we split it up so that Pat and I would drive twice on Saturday, and Evan and Sonny would drive twice on Sunday.

I decided that Sonny should start the race because he’s got the most experience, and track conditions were treacherously damp and cold. As we watched the race cars pull on track for the first time, I noticed frost on the stairs up to the viewing area, it was that cold. Sonny going first also meant he could be coach and crew chief for the team for the rest of the day.

Start your engines (and go backwards)

We began the race in 30th position, with all but one of the Class 3 cars ahead of us, and we slipped backwards immediately. Our momentum machine does not do well when blocked by traffic, and by the 5th lap, all the Class 3 cars were long gone in the distance, and there were nine Class 2 cars in front of us as well.

Sonny getting swallowed up on the race start.

Think about that for a minute. We qualified in Class 3, and a handful of laps later there were nine “slower” cars in front of us. That is not Sonny driving badly, that’s a lot of Class 2 teams not qualifying at their race pace. When the flag dropped, seemingly everyone could get another second out of their car. What a curious situation that is <cough>sandbag</cough>. Kidding aside, this is the problem of a momentum car, if you get blocked in one corner, it ruins the entire lap.

We wanted Sonny to stay out until the tank was dry, which would be about an hour and forty minutes, but he pitted around the 85-minute mark and found us a bit unprepared. Apparently he came together with a BMW in T6 (the right turn after Madness) and was afraid the contact might have damaged something.

Houston, we have contact.

So he rightly brought the car in right away. In fact there was damage, but we wouldn’t know the extent of it until later.

Nevertheless, Sonny did 48 fast laps in difficult conditions, and that brought us up to 29th position. But the long pit stop meant I started the race in 39th position. I lost another spot early on, but then settled into a rhythm and took some positions back. I set my fastest time of the weekend in that first stint, a 1:47.53, which matched my race-pace expectations from Friday. I pitted after 48 laps with us in P31.

Pat was next, and the driver change meant he started in P35. But he quickly went to work, and 46 laps later we were in 23rd position overall. He set his fastest time of the weekend about half way through his stint, a 1:45.373, and did some proper w2w racing. Somewhere around this time we also got reclassed to Class 2, which was appropriate. We then made the least of that opportunity by taking an unplanned stop….

Pat ran out of brakes. In fact, he could hardly get the car stopped going through the RFID gate! We fueled the car in the pits, but then immediately took the car to the garage to change brake pads.

Listen to the brakes as Pat tries to stop at the RFID gate.

If you back up that video 20 minutes, there’s some good w2w race action, including some oversteer saves probably due to the broken sway bar mount (but more on that later).

A short break for brakes

The fact that we wore out the brakes is totally my fault, because I should have put new pads on before the race. I’ve been using Porterfield R4E pads in front (Mu .46), and they have lasted for so long I thought they would last forever! I guess not. In all, I think I got 30-36 hours out of those R4Es, and I would consider buying them again, but being a lot more cognizant of pad life toward the end. On the plus side, they modulated well, and wore evenly. I certainly got my money’s worth.

I brought backup pads, StopTech Sports (Mu .40), which I’ve used many times in endurance racing. They have four redeeming qualities: cheap, last exactly one weekend, aren’t grabby (I’ve had problems with people flat-spotting my tires), and can handle a lot of heat. But StopTech Sports aren’t “race pads” in the sense that nobody takes them seriously, except for my brother and I.

My reservation with StopTechs were that I had never used them with such a fast team, and brake wear was obviously an issue. I also didn’t know where to set the brake balance vs the Porterfields, so I gambled and turned the prop valve two full turns to the front (it was full rear before this). We sent Evan back on track with the new brakes, and I went over to the Summit Racing truck to order new pads, which we’d swap out in the morning.

Summit didn’t have a lot of options for brake pads in stock: PowerStop (no), Centric (fuck no) and Hawk. Of the Hawk pads they could get me tomorrow, it was HP+, Blue, and DTC60. I ordered the DTC60. So as to not confuse them, I told them the car was a 2004 Miata, because the 2003-2005 all used the larger Sport sized calipers, which is what’s on the race car.

Back to racing

We lost 20 minutes changing brake pads and rotors, so Evan started the race back in 35th place. But Evan is our fastest driver, and he put in 56 laps that got us back to 23rd place. His 1:44.501 lap was the fastest of the weekend.

Evan with a triple pass (no audio).

Then I got back in the car for 27 laps and didn’t find my groove for a while. But I finally got settled and moved us from P25 to P23, and eventually set a time only 2/10ths off my previous stint.

Pat was our final driver, and started in P24. In the video below, his pass on a Porsche GT4 Clubsport ($165,000, 385 hp) is a good example of how to drive a momentum car, and pass cars that have three times the power.

Pat passes a Porsche GT4 Clubsport.

At the end of his stint we were P19 overall, and 5th in class. That’s pretty good considering a couple slow pit stops and a longer pause to change brakes. If we didn’t stop for brake pads we would have placed 15th overall and 2nd in class.

Overnight work

We got the car on stands, and the first thing we noticed was that the front left wheel was bent. This happened in the very first stint, when Sonny came together with a BMW. We got lucky that the tire held air the whole day, because it went flat later when on the trailer. The left rear was also pretty hashed from contact, and I’ll throw it out with the front.

The wheels are 15×9 Konig Helix, which have spokes that are proud of the wheel. Nobody should wheel-to-wheel race a car with spokes like this, and that’s on me for making a purchasing mistake. I’d bought these from Goodwin Racing on sale for $109 shipped, and I think the price outweighed my good sense. I will replace all of my wheels at this point, and move these to a HPDE car.

Another problem we found was a broken sway bar bracket. This is a weak point on a Miata, and there’s a simple cure – a piece of aluminum that braces the bar. Well, I didn’t have that and we had to go looking for another part in the pits. A generous team let us pull one off their car, and we got it fixed late that evening.

In the morning we’d get new brakes pads from Summit, put on wheels with four brand new RS4 tires, and win this thing. Or so we thought.

Mid Ohio, Part 2: Practice and Qualifying

Is this a racing team or the Comet Skateboards team?

American Endurance Racing (AER) is a top-notch racing series. This was my 24th endurance race, but only my second with AER. The memory of my first AER event at Watkins Glen is tainted by me crashing out in T6, and I had forgotten how professional this series is. For example, checkin is much easier, because your personal gear is your personal responsibility, and so they don’t verify all your stickers and labels and whatnot. If you treat people like adults, they act like adults.

Each driver and the car have RFID stickers, and with that they know exactly who is in the car at all times. On your AER profile page, that data is saved for you and the entire team. The pit stops are timed via RFID, as well. All very high tech and classy. You also get regular text messages throughout the event, telling you important details.

The cars are more expensive and faster than you’ll see in Champcar, Lemons, or Lucky Dog. Stacker rigs are not unusual, and so our open trailer stood out as an oddity. We were definitely the budget team against a lot of expensive BMWs, Porsche Caymans, and even an Audi R8.

Sahlen’s R8 sets the class.

AER events start on Friday, with an HPDE point-by session until noon. Non-race cars are allowed as long as they pass a quick tech, and so it’s not unusual to see street cars, including rental cars, on the track together with the race cars. This is a good opportunity to learn the track with a coach in the right seat. It’s not a good opportunity to learn the limits of a street car. One person in a rental car experienced stock brake fade and wadded their car. It did not look drivable afterwards.

Friday practice. Let’s get this show on the road!

We each took one run in the car. Sonny did the first run since he’s very familiar with the track (ahem, TT6 track record), and we wanted feedback on how the car handled. He said it was pretty good right away, and that our car should be capable of a 1:45, maybe a 1:44. He said this would be a decent NASA ST6 time. And when you consider we’re using the chicane, which adds a couple seconds, and we’re on RS4 tires, that’s not bad at all. In my previous blog post I wrote that OptimumLap predicted a 1:43.5, so that’s pretty close. But that would be a perfect lap, and we only just got here.

Pat has been to Mid-Ohio a couple times before, so while he knows the track, he had to re-familiarize himself with my Miata. Pat usually races a 265 whp E36 M3, and so I would imagine it takes a bit of time to get on the momentum line. Evan is a Miata specialist and knows how to get the spurs into a slow car, but had never been to the track before. Nevertheless, they both posted initial times that were similar to each other, and not too far off Sonny. Impressive.

I take longer to get adjusted to a new track, which is mostly braking too early, a slow entry speed, and other fear-based survival tactics. I did a shaky and uncertain 1:58. Thankfully we didn’t have the Aim Solo turned on, I really don’t want to see the data.

Coaching moment

We didn’t have time to look at the Aim data over lunch, but we watched video from Sonny driving the car, and that was illuminating. He explained where he was braking, turning in, shifting, etc. The big surprise to me is that it’s all 3rd and 4th gear, and I was shifting twice into 2nd. This is partly because I put in a couple hours sim time in Assetto Corsa, and was driving the stock NA car the same as my race car.

Sonny also carried much more entry speed, barely braking for T1, the chicane, T9, and T11. I chewed on this while chewing my sandwich, and prepared to go out again.

Image may contain: 2 people, people smiling, people sitting and indoor
Worst. Picture. Ever.

Practice and qualifying

The afternoon session is race cars only, in racing conditions. It’s still practice, but it’s also qualifying. AER classes you solely based on your team’s lap times, and there’s a secret threshold (maybe not so secret) for each class division.

I got in the car first, and was immediately more confident, knocking off over six seconds and did a 1:51.7s. Strewth, six seconds. That’s the difference between me trying to learn a track on my own, and literally 10 minutes of Sonny explaining the track to me. I need a coach at every race.

We each got two 20-minute practice runs each, and in my second run I did a 1:48. I had 8/10ths in hand on the next lap, and then felt the car sputter as I sipped the last off an empty tank. I nursed it back to the pits, but it was good to know I’m capable of a middle 47. With more track time throughout the weekend, that felt like a good target for a race pace, as well.

Pat’s times came down a bit and by his second session he was reacquainted with the car and solidly in the 1:45s. He came in with grass on the splitter, evidence that he was feeling comfortable and exploring the space. Maybe a bit too comfortable.

Sonny did a high 1:44 in the afternoon, which gave us an indication of how fast the car could go, and matched his forecast from the first time he sat in the car. Sonny said that he can determine the potential of a car in one lap, and often in just a couple of turns. Not an exaggeration. Fact.

And then Evan surprised everyone by going quicker, managing a 1:44.5. Holy crap this kid is fast. This is his time ever to Mid-Ohio, in his third 20-minute practice session, and he out-qualified our pro driving coach by .35 seconds. This kid had like 42 hours of racing time in his entire life before this event.

Evan Merrill. Two Rs, two Ls. Remember the name.

AER Class 3

So with both Evan and Sonny doing 1:44s, we got put in Class 3. My goal for this car was to be eventually competing in AER Class 3, and here we were! But mostly because we didn’t sandbag qualifying. We were still learning the track, and that required going as fast as we could. Most other teams held some in reserve so they could be classed lower (or classed appropriately, if you wish), and race for a win.

We were classed with these cars in AER Class 3. Seriously?

After seeing the other cars in Class 3, we went to the officials and said how did a 120 hp Miata, the least powerful car on track, get put into Class 3?Obviously it was good driving, but they said that if this turned out to be a mistake, they would re-class us half way through the race tomorrow, and put is in Class 2. Cool.

Pat adjusts tire pressure. Note the green “3” class sticker on the windshield banner. For realz.

But still, we did get AER Class 3 in qualifying, and for me, that feels like a million bucks. When I look over the cars we out-qualified, it goes like this: lots of BMWs (E36 325 S52, three E46 330s, all of the E30s, 525i), all the Miatas except one (two NC, two NA), three Porsche 944s, a Toyota 86 and a VW GTI. Fuck yeah.

Coaching moment

Friday evening we got a chance to look at the Aim data, and Sonny coached us on where we could improve. For me, the biggest problem was slowing the car too much. I always do that, but to a criminal degree in T1, T4, and T11. I also sometimes coast into or through corners, and lost a quarter second by not getting on the gas early enough in Madness.

Image may contain: people sitting, screen, table and indoor
Late-night coaching moments require IPAs.

But it’s not like I’m a total noob. There were some corners I did right. In the keyhole and esses (T5-8), I’m as fast as anyone. To understand this, Sonny looked more into the data, and my lateral Gs are identical to the rest of the team pretty much everywhere except T1, meaning I’m cornering just as hard. My problem is I throw away too much time before the corner. This is not new news to me, it’s my particular driving style, and something I will have to correct if I want to go faster.

Aero and setup notes

I saw a lot of great aero this weekend, with most teams running splitters, side skirts, venting, etc. Wings were mostly about roof height and about zero degrees angle of attack. This is much different than a typical Champcar race where you see wing angles set too steeply, wings mounted too low, or otherwise aero done wrong. I only had to threaten to dick-punch one guy, when he said his 190+ hp 2.7 stroker e30 didn’t make enough power to use aero.

There were other Miatas without aero, and they all had motor on us. In fact, we were the slowest car in a straight line. But the extra downforce gave us better cornering and braking, and was clearly felt in the high-speed sections on the track. One Miata with aero and more power was doing 1:42s and was a legit Class 3 car. They were on RE71Rs, though.

I’m still using a 60″ 9LR wing set at about 5 degrees, without a Gurney flap (the flap would add about 15% rear downforce). The front has a typical Supermiata-style airdam, and a splitter of 4-5″ length depending on where you measure it. We didn’t adjust the aero one bit, and the car was very well balanced and easy to drive.

Setup wise, we added two turns up on the left rear shock, which is a Mid-Ohio thing. Otherwise we left the car alone. We set the 225 RS4 tires at 24 psi cold, and they came up to about 30 psi hot, and we’d bleed them down to 30 if they went higher. A pyrometer verified this as the proper setting.

Mid Ohio, Part 1: Test Day at Pineview Run

The Occam’s Racers team will be racing at Mid Ohio on 10/18-20 with AER. The main team is Mario Korf (me), Pat Cornwall, and Evan Merrill. Pat races regularly with a BMW league, and he’s been on the Occam’s team twice before. He’s a fast driver, a good mechanic, and you can’t ask for a better teammate. Evan was one of the drivers at the Watkins Glen aero tests. His background is sim racing, and this make his racecraft very impressive, and his online speed somehow translates to the real world.

I’ve been looking for a fourth driver for this race, and found one: Sonny Watanasirisuk. If you follow Miatas, you probably know the name, he works for 949 Racing has won many a race and championship, and is a pro driving coach. Sonny will be joining the team primarily as our coach. Who am I kidding? He’s our ringer. I’m super stoked at this development, and I’m sure it will result in some humble pie, as well as a bunch of speed and setup secrets which I will share with you all. (Or not. Muah ha ha ha.)

But first things first. We have a car hasn’t been run since the WGI tests, and we wanted to address the understeering problem we had there. So we put the rear sway bar back on and corrected the negative rake. There were other things to do, like new shackle-style motor mounts, which should keep the header from hitting the trans tunnel. It was making an awful thumping sound and was really disconcerting.

With these and other details done, we loaded up and headed to Pineview Run for a team test day. I’ve been driving my 1.6 Miata at Pineview a lot, and the first thing I noticed about the race car is that it steers way better, probably because of more caster. On the other hand, the brake bias is way off. The front brakes are the larger 99+ Sport model with Porterfield RE4 pads, and the rear are stock 94 brakes with StopTech pads. This makes for a very grabby and front biased setup that will need to be corrected with a prop valve and possibly a pad change before the race.

We each took two turns in the race car, and logged data with an AIM Solo. This allowed us to compere dick sizes lap times, and see where each of us is fast. I had the fastest average lap (I have a lot more laps around Pineview and can drive it consistently), but they both put in laps that were outright faster than I could. It’s good to have teammates that are faster than you are. What was surprising is that while our times were fairly close, we have different driving styles. But more on that another time.

I also invited my 24 Hours of Lemons teammate, Tom Pyrek, down to Pineview Run, and he brought his racing minivan. Tom got into the Miata for a few laps, which was surprising because he doesn’t like Miatas. Evan got to drive his Neighborhood Trolley minivan in exchange, which was pretty dope. Then it started to rain, and the fun really began.

Here’s a couple videos of Evan in his NB Miata and Tom in the minivan. Rain is fun!

Evan on bald NT01s in the rain.
Tom in the Neighborhood Trolley, or boat, as it were.

In all, the test day went great. We had a lot of fun in the dry and wet, and the race car seemed much more balanced. (No video from the race car, sorry.) We’ll have to sort out the high speed handling when we get to Mid-O.

To get back to Sonny, he recently won the TT6 race at Mid Ohio, and I used his 1:40.7 lap time on the Pro Course to correct some values in OptimumLap. Based on the G values I saw in the video (around 1.3 g steady state cornering with higher spikes, but I’ll settle on 1.3 g) and rough Cl and Cd data (.48, .45), I was able to get the same lap time by changing course grip to 95%.

Sonny doing it at Nationals

Based on the data corrections, OptimumLap says my car should be capable of a 1:41.6 on the Pro Course (with Sonny behind the wheel). AER is using the chicane, which adds probably two seconds, so a projected lap time is more like 143.5. This is all preliminary guesswork, but time will tell. Literally.

Race Cars: Drag and Lift Examples

In a previous post I looked at how to calculate drag and lift using the HP Wizard drag calculator, and simulated lap times based on various modifications. This time around I want to look at some real-world race cars and use them as examples of drag and lift so I can play “what if”? Such as, what if my Miata was shaped like a NASCAR stock car? What would that do for performance? Or, what if I could make my Miata look like a LeMans prototype?

In the following table, imagine that each body is scaled up or down appropriately and would fit on a Miata chassis. The cars and assumed to be running with windows open, or however they run in their series. For the simulation, I’ll use 2400 lbs, 140 hp, with tires that grip at 1.1g (endurance tires), and 18 square feet frontal area.

For each car, I’ve calculated the lift/drag ratio, which is an indication of how efficient the body is at creating downforce. I’ll also simulate lap times at Mid Ohio Pro course (no chicane).

CarCdClL/DMid Ohio
Standard race Miata, no aero.45.45-1.0104.60
1990 Mazda RX7 GTO (spoiler).51-0.44.86102.76
1990 Mazda RX7 GTO (wing).48-0.531.10102.31
2002 NASCAR.39-0.461.0101.82
Miata, splitter, wing.48-1.012.10101.12
Miata, splitter fastback, wing.41-1.202.93100.11
Audi R8 race car.54-2.604.8298.12
Mazda RX-729P.70-3.805.4397.47

As expected, an aerodynamic body makes a big difference in lap time. A stock Miata doesn’t have a lot of drag, but it generates lift (positive Cl) while all the other body styles generate downforce (negative Cl). I’m not bashing Miatas, I love them. Virtually every street car generates lift and faces the same problems when used as a race car.

I thought the L/D ratio would be a direct indicator of lap time, but it isn’t. If it was, the RX7 GTO (wing) would have a faster time than the NASCAR body, but the stock car is slightly faster. While I chew on that, let’s take a deeper look at some of the body styles.

RX7 GTO

The 1990 Mazda RX7 GTO is particularly interesting because the spec body kit originally came with a rear spoiler, but this was later replaced with a wing. It’s nice to get these kinds of data points, it helps me correct my assumptions and make better estimates.

Image result for 1990 mazda gto
Early spoiler version, Cd .51, Cl -.44.

The earlier GTO version with a spoiler is a bad-ass looking car IMO. It probably has slightly better drag and lift than a Supermiata. They both have airdams and spoilers, but the GTO has side skirts and is a more developed shape. Take a look at what’s going on with the B-pillar vent, I’m not sure what that is, but it’s a good way to use air rushing past an open window.

I’ve previously written about spoilers on Miatas, and have used a theoretical Cd of .46 and a Cl of -.10 for some simulations. I may have underestimated both the amount of drag and downforce a spoiler can produce. I should probably re-run the data using a Cd of around .50 and a Cl of -.40.

Image result for 1990 mazda gto
Later version with a wing. Cd .48, Cl -.53

Comparing the two versions, the spoiler has .03 more drag, and .09 less downforce. This leads me to the following thoughts:

  • I would have expected the spoiler to have less drag than a wing, not more. Perhaps the fastback shape is already very efficient and there’s no need to spoil the shape?
  • If you add a splitter to the wing version of the RX7, it would have a Cd of around .47 and a Cl of about -.91. This is pretty close to my Miata’s measured .48 and -1.01. My race Miata also has side skirts and vents behind the fenders, and some other tricks. The difference between the two is probably the wing.

NASCAR, Miata, and other body styles

It’s kind of surprising how good the aero is on a NASCAR stock car, or at least the 2002 version I’m using here. It has a very low ride height, side skirts, a higher rear deck, and a spoiler. Stock cars also do a good job of keeping air out of the cockpit by using window nets, and also curved B-pillars that extract air from the cockpit. The L/D ratio is right in between the two RX7 GTOs, but the stock car’s lap time is faster than both. Wha?

Image result for 2002 nascar
A 7/8 scale Miata stock car would be dope.

When you compare all of the cars here, you can see that a Miata with an airdam, splitter, and wing has drag and lift values that are good. Race car good. Against a standard Miata, the aero version is 3.5 seconds faster in the simulation. A fastback drops another second, but most people won’t have the time or inclination to go that route. Which is fine, because it’s really the last piece of the puzzle. Or is it?

The Audi R8 race car and Mazda prototype are in an entirely different league. To get anywhere close to this level in a Miata would require a flat bottom (or venturi), diffuser, and other tricks. I intend on building and testing these things in the future, but a round-number goal is something like Cd .50, Cl -2.0, L/D 4.0. This would give a projected lap time around 98.8, which would be almost 6 seconds faster than a stock body Miata, and all this from body shape alone.

Pineview Challenge Cup – 300 Class Recap

The Pineview Challenge Cup series began last year, and was the club’s first competitive event. I blogged about that on my brother’s site, and joined the club shortly after.

In 2019 they made this into a series of six events, with one final round to determine the winner. I wrote about the simple classing systems in Time Trials on 300 Treadwear Tires, and felt like I would have the best chance in the 300 TW “Street” category.

I decided I would use this series of events to try different things. Each event I would change one thing or another, and see what the effect would be on lap times and feel. So, as you read through this, you’ll see what I’ve done to the car. Track conditions varied with each event, and I’m sure my driving ability did as well. So this isn’t a scientific test, it’s a log.

2018 Review

In the first running of the Pineview Challenge Cup, I put down a couple practice laps in the 1:24 range. This is always a good benchmark for what I consider my “endurance pace” on S.Drives. Meaning I can run this pace consistently, pretty much all day long.

But in the heat of competition, I can drop a fair chunk of time. On this day my fastest lap was a 1:21.7.

Best LapHPLbsCfCdCl
1:21.710624001.00 g.450.4

Event #1: +6 HP

Fast forward to 2019, and a new Challenge Cup series of events. The first change I made to the car was add some power. Over the winter I installed a Raceland header and a Magnaflow direct fit cat, but I haven’t had a chance to dyno it, or do any tuning. I estimate the car makes 110-112 HP based on a previous dyno run at Overdrive Automotive. It made 106 HP on their DynoJet with a DIY intake, Cobalt cat-back, and Megasquirt PNP2.

Before the airdam and spoiler.

Compared to 2018, my best lap improved by .25 seconds. OptimumLap says that adding 6 hp is worth .27 seconds, so that’s really close.

Best LapHPLbsCfCdCl
1:21.5511224001.00 g.450.4

Event #2: Airdam, spoiler, +ride height

For the second Challenge Cup I added a small airdam and splitter. I was worried about the splitter being too low, so I raised the ride height five full turns, or about 5.5″ at the pinch welds. This was probably overkill, but roads in New England suck. A couple years ago the car was lower and also had the R-Package front lip, and it would hit things all the time. So I was a bit paranoid about going too low, and might have overdone it going too high.

I also added a DIY 3.5″ tall spoiler to the trunk. So that’s a lot of variables at once: taller, chin airdam, spoiler. I’ll make a total wild guess on what that does for drag and lift, and increase drag by .02 and decrease lift by .4. The front and rear mods added about 10 lbs.

Best LapHPLbsCfCdCl
1:21.3911224101.00 g.46-0.4

I got second place because it was just me against a Corvette. I lost.

Event #3: Oil and water don’t mix

My 93 Miata has a 4.3 final drive ratio, and because of that, I bounce off the rev limiter or have to shift briefly into 3rd gear three times per lap. In the future I plan to replace the open diff with a 4.1 Torsen, but until then I need a solution. So I plugged in my laptop and changed the redline to 7500 rpm.

I also had a new DIY spoiler, with an extra flat piece of black plastic to make the height adjustable. I put in Paco Motorsports seat bolsters, and got a bit more aggressive on the seat foamectomy.

Best LapHPLbsCfCdCl
1:21.511224101.00 g.46-0.4

I only got one run in when a younger fella blew something in the Porsche he was driving and spun out in his own fluids. He was good enough to pull over and sit for the red flag. But then he got impatient not knowing what to do next, so he drove around to start/finish. He dumped fluids the whole time. ON THE RACING LINE.

He’s a young kid, doesn’t even have his driver’s license, and so his dad brings a car for him. Coolest dad ever, right? I’ll give the kid a pass this time for not understanding the meaning of a red flag. But I left Pineview after doing only one run, I don’t have patience to sit around for a track that will thereafter be slower.

That one run gave me second place behind Mike Filosi in a S2000 and in front of Dennis Rice in a Cayman S. Dennis is about 20 years older than me, but we have a good little rivalry going between us.

Event #4: Bad aero balance

For the fourth event, I switched my trunk lid from the one with a spoiler to one with a luggage rack. I can’t remember exactly why I did this, I must have been traveling somewhere. It was a mistake. Without the spoiler, the car oversteered badly. I probably also have too much chassis rake, and maybe the spoiler was covering up that problem. In any case, I was slower than other events.

The S.Drives are also wearing down quite a bit, and I keep expecting them to get faster because of less tread squirm. There are too many variables in the machine, the driver, and the conditions to know for sure, but I feel like the tires are giving up on me.

Best LapHPLbsCfCdCl
1:22.111224101.00 g.460.0

I got last place this time, out of 6 cars. A bit humbling, but that’s what happens when you upset aero balance and don’t have the skill to drive around it.

Event #5: Missed it

I missed the 5th event for a late work meeting. I would have placed third or fourth I reckon. Hal and his ‘vette did low 17s, and Mike got second with a high 17, and I can’t touch that. Dennis was fast and did a 1:20.7, he would have given me a run for it.

Event #6: Wet

I’d been waiting all year for a rain event, and this time we finally got a wet track! I took off the S.Drives, which are now down to about 2/32, and mounted the 205 Conti ECS. A lot of people like them in the rain, and they apparently don’t need any heat to work.

In the first session I did a 124.1, which was pretty good compared to the other cars, on any tire. And then I ran a 123.9 in the second set. I got held up by another Miata on crappy all-season tires and had to pass him, so I only got one run in on the second session.

We usually take a break between the 2nd and 3rd sessions, to eat burgers and BS, and then suddenly the sun started to come out. I didn’t need that, I needed a downpour! But the track didn’t dry out completely, so that was fortunate.

Best LapHPLbsCfCdCl
1:23.411224101.04 g.46-0.4 ?

In the final session I ran two 123.4s in a row, and that was good enough for first place in the 300 class. My first win! I also beat about half the cars in the 200 class, which was pretty satisfying. I even got close to Josh in his BRZ, he did a 1:22.8 on Z3s. Miatas are good in the wet.

Pineview Cup Challenge Final

I used the Conti ECS last time because the track was wet, but I know they are faster than the S.Drives in the dry, so I kept them on. Previous testing showed they are about 1.5 seconds faster than the Yoks, and so I was hoping for a 1:19 flat.

Lots of changes throughout the season, this is how she looked at the end.

I decided to remove the top and the passenger seat. This was the finals, you go all out, right? I went over a half second faster than I thought I would. Some of this was track conditions, they were really good, and Josh went under 1:15 in his group, and that doesn’t really happen for him on Z3s (but does on RE71Rs).

Best LapHPLbsCfCdCl
1:18.411223301.04 g??

I put the top back on for the last session (but not he passenger seat), but by this time the track was slower. I did a couple high 1:18s, which is only a couple tenths from what my car will do with 225 RS4s. The Contis are great tires.

In the end Hal Defrees won the final event, and the Pineview Cup Challenge overall trophy. He won every time he showed up, and never took any penalty points for going off track. That was enough to beat the rest of us, congratulations.

Image may contain: 7 people
Hal (smug), me (Lemons hat), Mike (Spec 13)

Calculating Drag and Lift From Body Shape

The HP Wizard website has an enormous amount of information, and I have a lot of fun playing with their drag calculator. Basically, you choose from various options and it calculates the Cd and Cl of your car. Let’s try this on a Miata.

I set the following options, which gives me a Cd of .380 and a Cl of .32, which is spot on.

  • Shape – Well rounded (2)
  • Front elevation – Low, rounded, sloping up (a)
  • Scuttle and Wing – Flush, rounded top wings (3)
  • Windscreen – Wrapped ends (2)
  • Windscreen peak – Rounded at top (1)
  • Canopy plan – Tapering to front (3)
  • Rear Canopy – Rounded canopy and boot (4)
  • Lower rear quarters – Tapering to rear (1)
  • Underbody – Monocoque RWD (4)
  • Skin friction – Recessed windows w/ mirrors (5)
  • Internal flow – Typical (4)
  • Openings – Closed cockpit (0)
  • Wheels – Fenders only, 205/50-15 (0.046)
  • Lift induced drag – Production model (Cl .32)
  • Frontal area 18.09: height (48.2) width (65.9).

Windows open and top down

Most HPDEs and racing organizations require you to run with open windows, and HP Wizard can simulate that. By changing Openings to “Open window prod car,” the Cd increases to .428. Or if you use the Miata as intended and open the top, then the Cd is .466.

Now this is interesting because my testing showed that opening the windows was much worse than .428, more like .450. In fact, the hard top with open windows measured worse than a completely open top. I’m still trying to get my head around that. I didn’t test an open top without a wing (no time, and it’s not a racy configuration), so it’s possible the wing actually helped the open top create less drag by smoothing airflow behind the car. Dunno.

In Race Car Aerodynamics, Katz measures the effect of open windows on passenger vehicles and race cars, and a typical sedan loses .067 drag to open windows and .09 to removing the top. So again, this is perplexing why the Miata in particular is so bad with open windows and a hard top.

So I’m just going to stick with a closed-windows model for the rest of this investigation.

Lift and downforce

The HP Wizard calculator can also calculate lift. If I choose the standard production model options, then my Miata model has a coefficient of lift (Cl) of .32. That’s pretty accurate based on other data I’ve seen. Let’s use the calculator’s lift options and see what happens to drag and lift as I lower the car and add downforce.

As usual, I’ll also simulate lap times on a race track (this time VIR). I’ll use a stock Miata (2450 lbs, 4.3, 1.0g tires, etc) and try it with 93 hp, and then I’ll add 50 hp because who has a stock Miata?

Lift-induced dragCdClVIR 93 hp143 hp
Production model.380.32151.52141.29
Sport.378.20151.18140.86
High performance.378.151:51.06140.7
Diffuser.377-0.10150.45139.88
Production race car.377-0.50149.57138.67
Speedway Miata (?).503-1.90149.73137.30
High downforce Miata.806-3.50155.35139.88

Reducing lift (downforce) yields faster lap times, to a point. A Speedway Miata (if such a thing exists) needs a lot of power to overcome the drag. The high downforce version has so much drag that even 143 hp is not enough.

Another thing worth calling out is the diffuser. The Miata underbody is anything but flat, and a diffuser would work better with a flat bottom, but this tool doesn’t allow us to make such adjustments. Anyway, the tool says a diffuser will reduce drag slightly and increase downforce by about .25. If that’s true for a Miata, this is totally worth doing.

Reducing drag with a fastback

In the above simulations, drag turned out to be a lot more consequential than I would have thought. Let’s see about reducing drag with a fastback. Based on real-world tests of my fastback, this could be up to a .07 reduction in drag.

First, I’ll modify some values in HP Wizard and change “Rounded canopy and boot” to “Fastback 10-20 degrees,” and the Canopy plan to “Tapering to rear”. Right away the Cd goes from .380 to .333.

The next thing I see on the Miata is the hard top extends wider than the windows, and catches air moving along the car. My fastback doesn’t do that, so I’ll change Skin Friction from “Recessed windows” mirrors, to “Perfectly smooth body with mirrors,” and now Cd is .323.

That’s a total of 0.058 reduction in drag, which is really good. Not quite as good as my fastback, but I’ve also added some vents for internal airflow. So let’s clean up the internal flow from “Typical” to “Good Design” and the Cd drops to .314, which is a .066 reduction, and getting close to the .07 delta between an OEM hard top and my fastback.

So there’s no magic to a fastback’s drag reduction, just some simple things that are easy to calculate. The fact that a fastback also made my wing produce 20% more downforce was a pleasant surprise.

E30 fastback?

I’m not really a BMW guy. My brother used to have a chipped 325e (now with WINsome Racing), and we had that car plus our Miata and MR2 at Thunderhill, 3-mile, all on the same day. I loved the torque and sound of the straight six, and I went fastest in that car. But something about it and me never clicked.

On the other hand, Anthony Zwain is a BWM guy, and owns EDGE Motorsports in Mountain View, California. After the WGI aero test, Anthony and I started fantasizing about turning a E30 convertible into a fastback. The convertibles are heavier due to chassis bracing, which is a good thing, and the fastback roof would offset that by being very light (probably 20-25 lbs total). It could be a shooting brake or fastback. The sky’s the limit with a convertible.

Image result for e30 convertible
Imagine the possibilities….

You wouldn’t necessarily need a convertible to do this. I can imagine someone simply cutting the C-pillar, jumping on the the rear of the roof until it bent to about 12 degrees, and welding it back again. You’d need new side and rear windows, but those should be Lexan anyway.

Anthony. WINsome. Shut Up. One of y’all should do this.

“My Car Doesn’t Make Enough Power to Use Aero.” Ow!

I don’t know how may times I hear this phrase: “My car doesn’t make enough power to use aero.” After reading a lot of forum and social media posts, there appear to be two main camps people fall into.

  • People who believe that adding downforce always adds drag.
  • People who set their wing at too much angle.

The first group of people are simply wrong. Perhaps it’s because they are thinking in terms of increasing downforce rather than reducing drag. Lots of things that reduce drag also generate downforce as a byproduct. Airdams, splitters, and spoilers have all been proven to reduce drag. And they increase downforce as well. I haven’t tried a flat underbody and diffuser yet, but when I do, those will surely reduce drag and add downforce as well. If you don’t believe me, believe Kyle Forster.

The second group of people probably don’t understand that most wings work in a very narrow range of angle. The shape of the roof, and the location of the wing, both play a large role in the angle the wing. Whenever I walk the pits I have to bite my tongue. I see a lot of wings with too much angle. I’ve never seen a wing with too little.

The fact is that Miatas don’t have great aero, and the first generation especially can reduce drag and gain downforce without any loss of power. Let’s get into this in more detail.

Airdam and splitter both reduce drag

If you think you it takes more power to use an airdam or splitter, you’re wrong. Miata’s have exposed front tires and a nose that deflects air under the car. Adding an airdam lowers drag and lift.

There’s a great CFD study done by the Hancha group (now also posted by Velox) that shows the effect of various front-end combinations.

In the chart, compare #2 (lowered Miata) to #5 (lowered Miata with Supermiata style airdam).

In the CFD study, the airdam reduced drag by a full 0.1 which is astounding. This resulted in 10 more horsepower at 100 mph. The change in downforce was equally impressive, with a delta of 175 pounds at 100 mph. Shocking stuff. I didn’t get to test these front-end versions myself, so while I wouldn’t put faith into these exact numbers, it’s certainly true you reduce drag and gain downforce with an airdam.

Based on the fact that you get free power and downforce, why wouldn’t you use an airdam? Despite what many people think, you can further reduce drag and add more downforce by adding a splitter.

The splitter in CFD Setup 6 decreases drag by a further .02 over the airdam, and increases downforce by 49 pounds. My actual testing showed a decrease in drag of .01 and an increase in downforce of 68 pounds, and this was with a suboptimal chassis rake. You can believe computers or believe real-world testing, either way, airdams and splitters give you less drag and more downforce.

Spoilers give you something for nothing

You don’t need extra power to use a spoiler. In fact, spoilers often decrease drag, giving you more power. If you have a Miata with a stock trunk and the class rules permit it, use one.

Based on data in  Race Car Aerodynamics, I can make the following generalizations.

  • A low spoiler, about 1″ tall, gives you the greatest reduction in drag. It also gives you a bit of downforce. I call this a win-win.
  • A spoiler of 3″ tall has about the same as drag as a stock trunk. However, you get about double the downforce you got from the 1″ tall spoiler. I call this getting something for nothing.
  • A spoiler taller than 3″ begins to create a small amount of drag over a stock trunk lid, but it adds downforce at a greater rate than it increases drag. As you go higher and higher, this is the gift that keeps on giving. I dropped .55 seconds at Pineview Run (a low-speed 1-mile course) by using a 7″ tall spoiler vs 3.5″. I wasn’t able to increase the height any more than that, but it’s possible that going higher is even better.

Doing any of the above is smart. Using an adjustable spoiler is even smarter, it allows you to experiment and fine tune the balance.

Image result for blackbird spoiler

A wing doesn’t require (much) power

I use a 9 Lives Racing wing at 4.5 degrees and this measured to a .03 difference in coefficient of drag, no matter which roof I used. That’s about the same as your two side mirrors combined. If you don’t think you have enough power to use a wing, move your mirrors inboard and stop arguing.

But let’s put some real numbers to it. I’ll use the RSR calculator to see how much power it takes to run a car without a wing, and with a wing. (2300 lb, 18 sq ft frontal area, .45 Cd without a wing, .48 Cd with wing).

SpeedNo wingWingHP lost
60 mph18.1 HP19.1 HP1 HP
80 mph38.6 HP40.7 HP2.1 HP
100 mph71.5 HP75.7 HP4.2 HP

So you can see that a wing isn’t a large source of drag unless you’re doing 100 mph or more. And even if you’re clocking less top speed at the end of the longest straight, you’ll be going faster around the track everywhere else.

Wing angle and location

If you run a single-element wing at more than about 10 degrees, you’ve created an air brake. This is because the air separates rather than stays attached, which causes a lot more drag. You don’t create more downforce when your wing is set too high, you create less.

The roofline of most cars creates downwash, and this effectively changes the angle of attack. In the image below, you can see that a wing placed low increases the angle of attack and the amount turbulence. A wing mounted higher up and further back has cleaner air, with less a bit less downwash.

Putting a wing on this car at 5 degrees AOA would be a mistake. I’d run the wing at zero AOA.

If you’re using a wing and you’ve lost a lot of speed, reduce your wing angle and try again. A lot of wings have the best lift/drag coefficient (the most efficiency) right around zero degrees. As evidence, look up; planes fly around like that all day.

Use aero and profit

There are a lot of ways to add downforce that don’t require more power, and many combinations that work well together.

Spoilers are cheaper than wings, and splitters can get damaged easily. So there’s a lot of sense in running a less expensive, more durable, and more streamlined airdam-spoiler combination. It’s the Supermiata formula, and I think it looks better on a street car.

However, adding a splitter and a wing will make the car go faster around corners. The .02 change to Cd results in a paltry 1.5 hp loss at 80 mph. This is barely worth talking about.

I see that some cars are using a wing and airdam, but without a splitter (I updated this paragraph after reading the comments section). I guess that works for some people, but that combination made my car push everywhere, and boring to drive. Someone who can set up a car could probably dial this out (not me). But I’ll never understand someone using an wing and airdam, and not a splitter, the data just doesn’t support that being a better option.

Likewise there are probably some backwards people who will use an airdam and splitter without any rear aero. If you can get that to work, good on ya, but it didn’t work for me. My street car has an airdam and small splitter and I swapped trunks to one without a spoiler, and the car was loose and hard to drive at the limit.

Whatever the case, aero can make your car handle better, look better, and go faster around the track. Despite what people think, aero doesn’t require power. On a Miata, it’s usually the opposite.

The next time I hear someone say “My car doesn’t make enough power to use aero,” I’m going to punch them in the dick.