Deep Fried Donuts

» Posted by on Jun 12, 2012 in Current projects and Tech Notes | 2 comments

Deep Fried Donuts

If only I had taken my own advice…

In Think Fast, I made this bold claim: “New tires are awesome, but they are only awesome once. The performance drop after the first race is more than any driver can overcome. There is no point in showing up for a race that you hope to win if new tires are not in the plan. You really don’t have a choice here. There are ways to budget-down every part of the event except for tires.”

Yes, I made that mistake, and I won’t make it again.

Racing tires are made from very soft rubber, so they grip the pavement amazingly well when they are new. But soft rubber gets harder with exposure to heat and mechanical strain. The tire rule for the Pacific Formula F Super Series is that you have to run the same set of tires both days. There is at least one qualifying session and a race each day. I made a brilliant last-minute decision at Buttonwillow to buy a set of conventional medium compound FF tires instead of running the front tire size all around. That decision transformed the car into a stable, predictable, confidence inspiring, and much faster racing machine. However, since I had two simultaneous reliability issues on Saturday, I was only able to run the Sunday qualifying and race there. The tires felt just as good at the end of the Sunday race as they did at the beginning, and my lap times in that race were very consistent. So, I concluded that the Hoosier R35A compound was durable enough to go at least one more full day, maybe even two. Plus I had spent a small fortune that weekend, so I needed to get through the next event without spending as much money. A set of FF tires costs just over $1000, so it’s the biggest single expense in a racing weekend.

Only 3 weeks after the Buttonwillow weekend, the pro series ran the infield Sports Car track at Auto Club Speedway in Fontana, California. Kenton Koch volunteered to crew for me, even though we had only met once briefly at the Laguna Seca MX-5 Cup event. Thanks Kenton!

The superspeedway is the one that NASCAR competes on once a year, and the one that Gil de Ferran ran a 241.426 mph qualifying lap on in 2000 in a Champ car. It’s a for-real, prestigious, high speed professional race track. The sports car track uses the front straight and turns 1 and 2 of the superspeedway, then zigzags back and forth through the infield. My car accelerated to 134-136 mph on the front straight, and the tire drag from 1.6g of lateral acceleration through turns 1 and 2 pulled the speed down to 130-132 mph while at full throttle the whole time. It was a real thrill to drive on a real superspeedway near the top speed of my car, pull some real g’s in the corners, and pretend to be a real race car driver.

Fortunately, there are some good in-car videos of the ACS race track on YouTube, so I was able to learn a lot about the track by studying them closely. I learned most of the track fairly well right off the bat, but there was a slow right hand hairpin turn just after a flat-out left/right lane change that I never got close to driving right. Part of that is inexperience on that particular track, and part of it is rusty driving skills. I think I’m down to about 40 lb of rust on my skills, and improving from my current state is going to be much slower and much harder. Still, my skills are coming back a lot faster than they did the last time I re-learned how to drive, so I’m not too disappointed by my current state. I have a whole 3 races under my belt now. That’s not much. The key advance that I need to make is pushing the braking points far enough downstream. That is doubly important with slicks on a light car because hard braking is required to re-heat the tires back up into their best-performing temperature range. Tires gain and lose surface temperature at a very high rate. I will have a lot more to show you about that when I finally make the mounts for a set of 6 IR tire temp sensors.

From the first lap of the first practice session, the car had a terrible understeer in the slow corners. It was close to neutral in the 2nd gear corners and loose in the 3rd gear corners, but the oversteer was easily controllable. If I backed off the throttle or steering, the car would recover from the slide. Knowing that, I was able to drive it with the tail hung out in the faster corners. Still, the major problem was understeer in the 1st gear corners. It was really, really bad. I couldn’t get close to the apexes in those corners unless I slowed the car dramatically.

I started the weekend with a normal spring and anti-roll bar combination, with 250 lb/in front springs, 350 rears, and both bars in the middle of their adjustment range. I made both the front and rear anti-roll bars cockpit adjustable during the car build, so I adjusted the front bar to full soft and the rear bar to full stiff on separate laps during the first practice. That helped the understeer problem, but not much. I’m disappointed by how little balance change results from the bar adjustments. Perhaps they will be more useful when the balance is close to neutral to start with.

OK, so I had a setup challenge to tackle. I can do that. I chose to attack that challenge in small steps since changing the setup to reduce understeer in the slow corners could make the car dangerously loose in the faster ones. After nearly killing myself a couple of times on the skinny rear tires at Buttonwillow, I had no desire to risk crashing at ACS.

After the first practice session, we swapped to 450 lb/in rear springs. During the Saturday qualifying session, the low speed push was just as bad, and the higher speed oversteer wasn’t any worse. In hindsight, it’s clear to me that the front tires were used up during the Buttonwillow race, and they just continued to get worse every session at Auto Club Speedway. The setup changes were just chasing the deteriorating front tires.

So, before the Saturday race we swapped the rear springs again to 550 lb/in. Those are the stiffest springs I own. The FF field shrank to 4 cars for the race when Ethan Shippert bent a wishbone and didn’t have enough time to fix it for the race. So, I started 3rd and only had to build and maintain a gap to Sage Marie to get another podium finish. Here is the video of the Saturday start and the first lap. The behavior of the car was about the same during the race. Sage got a good jump on me at the start, but I was on the inside going through NASCAR 1 and 2, and was able to brake later before diving into the infield. I was able to keep Ed Erlandson and Conner Ford in sight during the first lap, but I fell back a bit through each corner. I fell back a lot through the critical corner leading onto the front straight, and I had the track to myself for the rest of the race. I was able to drive the full race distance off the pace but consistently, with one exception. I fell off the track in the hairpin that I never learned, but kept it running and rejoined without losing a position. It was a lonely race, but a podium finish! So, I got a nice trophy, got to pose for photos with the trophy girl, then got a dud bottle of champagne so there wasn’t any spraying from me.

Since the incremental spring changes had not fixed the low speed understeer, and the higher speed oversteer was no worse, I decided to make a bigger spring change for Sunday qualifying by swapping the front springs from 250 to 170 lb/in, and I left the bars at full soft front and full stiff rear. I also lowered both the front and rear ride heights since the car wasn’t bottoming anywhere, even over the really rough final corner. By that time, I knew for sure that the front tires were dead, and I wanted to preserve whatever was left of them for the Sunday race. So, I ran the first 12 minutes of the 30 minute qualifying session, then sat in the pit lane until there were 7 minutes left. During that outing, the tires were significantly worse, so I didn’t improve my qualifying time.

Ed, Conner, and Ethan qualified very close to each other, with Sage and I about 2.5 seconds back. After qualifying, my front tires were gone, gone, gone. It was going to be tough to get through the race. The last possible thing I could do to make life easier on the front tires was to disconnect the front bar, so I did that. Surprise! The car was nicely balanced during the Sunday race. It had a serious grip deficit, but it was more fun to drive. The decent balance was a result of hobbling the rear tires, not improving the fronts. Here is the video of Sunday’s first lap. The car had power oversteer coming out of the slow corners, which I reduced by softening the rear bar. The left/right lane change that had been flat easy wasn’t any more, and I had to really fight to keep the car down in the bottom lane through NASCAR 1 and 2. About midway through the race, I tried driving the second lane on the banking to take it easier on the tires. Big mistake. By then, the buildup of marbles made it really slick. I had to lift big time to keep the car from sliding up into the wall. After that, I was able to keep it in the low lane, but it was only just barely flat because the tires were so degraded. So, I can claim to have actually driven a superspeedway corner at the limit. I’m pleased with myself that I have the confidence required to do that.

Late in the race, I passed Ed while he was getting back on the track after an agricultural excursion. Due to my deficits of grip and skill, he chased me down in 2.5 laps and just barely got by me going into the infield. He slowly pulled out a 10 car length lead over the following lap, then fell off again. Back into the podium positions! Right up until I saw that black DB-6 in my mirrors at the beginning of the last lap, that is. He got by me going into the corner that I never figured out, but got a bad launch onto the following straight so I caught up to him. We had a rather lame late braking contest going into the final sequence of turns, which was settled in his favor since I never got my nose ahead of his. So, I followed Ed to the checker and a 4th place finish.

After the maintenance thrashfest that was Buttonwillow, it was a giant relief that the car ran all day for two days in a row. It was great to have the reliability issues behind us and be able to focus on performance, what little there was of it.

Lesson learned: New tires for every pro event, no matter what.

And one more thing: The last remaining vestige of adapting the car for skinny rear tires is the 40 pounds of lead in the tip of the nose box. That will come out and be replaced with a series of ballast plates that can be located in several places along the length of the car. With that, I will be able to fine tune the front to rear weight distribution in fine increments, and hopefully arrive at the optimum weight distribution.

2 Comments

  1. Neil, In your book “THINK FAST…The Racer’s Why-To Guide to Winning” one of your main foot stompers was new tires! If more racers and spectators would read your last race play-by-play, they would realize why tires are so important. Just look at what the Indy Car and Nascar guys do in the pits, two or four tires and gas. If tires were not that important, just think of the time saved in the pits if they just needed a fill-up, especially if they had only a few laps on the tires between pit stops. New tires or “stickers” as some call them always make the car handle better. Good luck in your next race.

  2. Great writeup again, definitely cool to follow your endeavors.

    FWIW, I don’t anything about FF tires but the few times I ran Hoosier slicks, the fall off between events was very noticeable. Again, I don’t know what THE tire is for FF but for our racing the Goodyears stay consistent longer.

    Turbo