"Mr. Toad" at Thunderhill (7 October 2021)"Mr. Toad" at Thunderhill (7 October 2021)
 Leading the pack |
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Sparring with Ray Allustiarti in his black Miata |
 Running away from Ray Allustiarti |
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 Germans in hot pursuit |
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This was my second time on Thunderhill's 5-mile course, a combination of the original leggy 3-mile east track and the newer and tighter 2-mile west track. Some people don't like it because the two sides are so different but I enjoy the juxtaposition of the two styles: the expansive east side is suited to the power of my car whereas the tight turns of the west side seem more amenable to the handling of a Miata, yet I've learned how to manage it.
Due to the length of the course, GGLC had just two run groups. Last time, each group had a 30-minute session, but apparently some people thought that was too long so for this event they ran 25-minute sessions. This was awful, in my opinion. First, it left time for few hot laps between the out lap and the cool-down in lap. Second, it left just a 25-minute dwell time between sessions, which without a support team wasn't enough to measure tire pressures and brake temperatures, make any adjustments, and just collect one's wits before going back out. The quick turns from session to session were very stressful.
My best lap of the day was 0.654 seconds faster than my best last year, benefitting from more experience on the west course in July—and more experience with the track in general.
This improvement was despite running on slippery tires (see below).
With better tires and a better run schedule I might have improved my lap time even further but I was still happy with the day's results.
Although this was a satisfying track day, it could have been better with better tires. My Bridgestone Potenza RE-71R tires had badly let me down two months earlier at Laguna Seca. Yet again, they precipitated the start of a spin (after Turn 11E) but I was able to catch it and recover before things got crazy.
They also let me down braking for Turn 14E,
where it was abundantly clear that my brakes (often a nemesis) were far
more capable than my tires.
I ended up braking early beacuse the tires weren't up to the job.
The following table summarizes tire pressures throughout the day, in PSI:
rotor caliper Description Time Ambient LF RF RR LR LF RF LF RF before session 1 0806 51°F 34 34.5 34 34 31 31 31 31 reset after session 1 0857 59°F 38 38.5 36 36 35 35 34 34 reset after session 2 0951 59°F 36 36.5 34 35 35 35 34 34 reset after session 3 1043 60°F 36 36 34.5 35 337°F 329°F 268°F 286°F after session 4 1127 64°F 37 37 35 36 416°F 429°F 329°F 340°F 35 35 34 34 reset after session 5 1207 64°F 34 34 34 34 355°F 338°F 277°F 270°F before session 6 1311 64°F 30 28.5 31.5 31 99°F 96°F 102°F 101°F after session 6 1345 69°F 34.5 34 34 34 360°F 340°F 285°F 287°F after session 7 1445 68°F 34 34 34 34 350°F 323°F 275°F 289°F after session 8 1538 68°F 33 33 34.5 34 253°F 230°F 221°F 211°F after session 9 1602 68°F 34 34 34 34 368°F 336°F 256°F 253°F end 1701 68°F 30 29 31 31
My target was to keep pressures to 35 PSI front and 34 PSI rear at the end of the session. With the short, 25-minute breaks between runs the tires didn't have much chance to cool and lose pressure; with little time to spare I didn't bother to check pre-session pressures except at the beginning of the day and after the lunch break.
The lunch break of over an hour before session 6 meant that session started with very low tire pressures, especially in front, and for nearly half the session the car handled like an old Buick as the mushy sidewalls caused the tires to roll in turns. Handling eventually improved as the tires warmed and increased pressure.
This was my second track day after replacing the fog lights with brake-cooling ducts ("fog darks"), and the first track day where I pushed the brakes very hard. I recorded temperatures for the front brakes, both at the top of the rotor and in the middle of the caliper but with braking limited by tires, and no solid baseline data, I didn't learn much yet.
As usual, my tires picked up plenty of OPR (other peoples' rubber),
mostly towards the outside as seen at right. I've never perceived any
impact of this extra baggage other than a rough ride for the first
30 minutes or so of the drive home.
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Copyright © 2021-2022 Karl L. Swartz. All rights reserved. |
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