Mid-Season Race Update, part 1
We're now at the long mid-season break between events and I can catch up on the last two. There were a lot of surprises and things to work on.
CFRA Round 4: Buttonwillow Raceway, April 27
Buttonwillow is different from the other venues in many ways.
The first thing you have to deal with is the meager hotel and restaurant situation. The hotels at the Buttonwillow freeway exit (ten miles south of the track) are cheap ($50 to $60) but the quality varies and is never better than "at least it's clean". The club designates one of them as "official" and most people stay there. After a couple of years at a marginally decent place, last year we tried a different hotel and it was really awful. The members voted to go elsewhere this year. Unfortunately, this place (Willow Inn & Suites, don't let the photo fool you, it's a wasteland) was lousy in different ways. To start with, it's under reconstruction; naturally they don't tell you this ahead of time. There's lumber, equipment, scaffolding, and piles of sand all over the place. Next, half of the rooms are backed up right against interstate 5. Traffic blows by, and trucks gear up to merge with the highway traffic, all within 40 yards of the rooms, so it's always loud. And finally, their advertisement of "free high-speed wireless internet" is false. There was no signal from my room, and when I tried it from the registration desk the signal was barely present and no connection could be established at all. This place is a disaster. For next year the club has voted to get up an hour earlier and make Harris Ranch the official event hotel. As far as the Buttonwillow exit goes, it seems like Motel 6 and Super 8 are the way to go by default. And if you're driving there from the Bay Area, you may as well stay at the Motel 6 in Lost Hills—same distance from the track as the Buttonwillow exit, but 20 miles closer to the Bay Area.
The circuit itself is unique in a several respects. The obvious thing is that it's nearly pancake flat. There are tiny five-foot-high hills at Cotton Corners and Lost Hill, and that's about it. None of the other Northern California tracks is anywhere near this flat. It's boring in terms of elevation change. Another unique thing about Buttonwillow is that it has two really high-speed connected corner transition sequences. The first is Club Corner and Bus Stop; the second is the exit of Riverside leading to Lost Hill. Both of these sequences challenge you and your car, because you are carrying a lot of speed where you have to pull the car right and then left in quick succession. I estimate that I turn right at Club Corner at 80 MPH, turn left at nearly 90 MPH and brake at the end of Bus Stop at 95 MPH; exit Riverside somewhere in the 80's, turn left up in the 90's, and brake for Lost Hill at 105 MPH. The challenge is to get your foot on the floor as early as possible, which requires total confidence in what the car is going to do when you turn. When my original suspension was starting to go a couple of years ago, the first indication was a very unsettling twitch when I turned left into Bus Stop. I'd never felt the rear end twitch quite like that in a high-speed corner, and it took me a while even after upgrading the suspension to get the confidence back and improve my speed through that section. The last thing to mention about Buttonwillow is the track surface. A lot of it is getting really old and slippery. I find the Cotton Corners sequence in particular to be like ice (but more on that problem below).
We had good weather, avoiding the extreme heat that can be a problem at Buttonwillow for a lot of the year. It was sunny and reached the 80's at the afternoon peak. My goal was, as usual, to set a new personal best lap record and to have a clean race. I'd done a 2:15 in 2002, but my times stagnated at 2:17 in late 2002 and 2004, which probably had something to do with the suspension getting worn out. After replacing the suspension with the Bilstein/TRG setup in 2005, I managed a 2:14.858, and in 2006 was only able to do a 2:15.873, perhaps due to track conditions not being ideal.
Practice & Qualifying
In the first morning practice session, I put down a 2:14.216. The Cotton Corners complex was slippery and understeery as usual, but I figured that a 2:13 would be doable in the next session or two, since my lap times almost always get better in the second and third sessions. However, in the second morning practice session, I only managed a 2:14.565. I checked the tire pressures and everything seemed fine; I already knew that this would the be the last day for this set of front tires, so I wondered if they were starting to get past their effective grip lifespan even though there was still no sign of cording.
Professional racing teams do so much tire testing that they are able to determine exactly how their particular tires' performance improves and degrades over their lifespan, and exactly how they behave at different track temperatures and tire pressures and with different suspension setups. But for us weekend amateurs, there's a lot of guesswork and ambiguity involved. If the car feels slippery, it could mean the tires have had too many heat cycles, or the pressure is not right for the track temperature, or the track surface conditions are poor, or the suspension is not optimally set up for the track or a particular corner. Some people are really knowledgable about this stuff or can quickly identify the problem through the feel of the car. I'm not one of them, so I tend to stick with a known reasonable setup and just complain about the lack of grip.
We went out for qualifying after lunch and as much as I tried, I barely broke 2:15 on a couple of occasions and ended up with a best lap of 2:14.752. The ambient temperature and tire pressures were still OK, so by now I guessed that the tires were indeed becoming heat-cycled out and the 2:13 was not going to happen. My qualifying lap of 2:14.752 put me 11th on grid, with a 3-second per lap advantage over the next fastest car in my class, Laurn's turbocharged Miata at 2:17.346. I was also gridded just ahead of (actually next to) Pete's Winston Cup car; I knew this would make the start a bit more difficult, because his car is so loud that it's disorienting as you try to hear what your own car is doing so that you hit your shift first point correctly.
Gridded after Pete was John's Lotus Exige. I expected both Pete and John to pass me at the start or soon after, leaving Laurn immediately behind me. With an expected 3 second per lap gap to Laurn, I figured that after the first lap of close traffic, I would slowly pull away from Laurn and the other cars in my class. I planned to use my brain and not battle hard with other cars not in my class, and just focus on driving a clean, mistake-free race.
Race
I managed a good start and stayed ahead of Pete for a couple of corners, but then he and John got by easily under power. In the tight sections of the track, the car seemed to be understeering even worse than before. After one lap, Laurn was 2 seconds behind. My lap times were all 2:18's and this allowed Laurn to catch up after a couple of laps. For the rest of the race, Laurn was all over me through the tight sections but had no opportunity to pass, and I would pull away a bit through the fast sections. It wasn't until the final lap that I broke 2:18 with my best race lap of 2:17.937. The lap times confirmed what I felt: I was going a lot slower in the race, and that's why I had a serious battle on my hands. I ended up 12th, first in the R-5 class, a tiny 0.636 seconds ahead of Laurn across the line.
Well, That Would Explain It
At the start of the drive home, on a couple of occasions I heard a loud thunk in the area of my left rear wheel. I couldn't figure out a pattern to it, such as turning or hitting a pothole or running over debris. It made no sense. The car felt OK to drive. And still, for the whole drive home, every once in a while there would be that thunk.
When I got home I looked under the car to see if there was any visible problem. There, dangling from the left rear drop link was a 1-foot section of my rear sway bar. The bar had snapped near the left bushing, and the dangling end was probably just grazing a Botts dot every so often on the freeway, flinging around and thunking against the trailing arm. The broken sway bar would certainly explain the severe understeer during the race. I was essentially driving with no rear sway bar; this means the rear end of the car was "soft" and compliant, giving too much body roll but lots of grip on the rear tires, and relatively speaking the front end with the working bar was too stiff and unable to grip well. When the rear grips better than the front, you have understeer. In simple terms, it means that the front of the car refuses to turn as much as you want, and it forces you to take the corner more slowly; if you don't slow down you simply fail to make the corner and you put your outside front wheel off the track first as you head into the dirt.
Since getting the Bilstein/TRG suspension parts, I've done very little to adjust the setup. I've left the rear sway bar on soft (it has two settings) and the front sway bar on medium (it has five settings). I've generally set the shocks to full stiff or one notch away (there are 9 positions on the PSS9). With the broken sway bar having such a dramatic effect on the car's handling, it made me realize how much more I may be able to get out of the car by making some adjustments. If the car is understeering, why not try putting the rear bar on the stiff setting, or moving the front bar one notch softer? Or doing something similar with the shocks. The shocks are adjusted with a dial that can be reached easily by just lying on the ground and reaching behind the wheel. Adjusting the bar requires jacking up both sides of the car at once, then removing and replacing the sway bar connecting bolt on each side. So the shock adjustment is easy but the sway bar adjustment takes a few minutes and requires jack stands for safety—I usually don't carry jackstands with me to the track. But I should probably take a stab at setting up the sway bars differently at home for the next event, and see if I can reduce understeer that way.
