"Mr. Toad" at Laguna Seca (3 September 2021)"Mr. Toad" at Laguna Seca (3 September 2021)
 Turn 8 (The Corkscrew) |
 Leung's Miata, Mr. Toad, and Greg's MINI Cooper |
 Andy Ward's green Porsche Boxster S and his friend's Pontiac Solstice Coupe |
Proper attire enhances speed!
 Comparing finish socks with Greg Epstein |
These photographs show the remains of the Hyundai Veloster which was wrecked at the top of The Corkscrew during the first session.
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At Laguna Seca in March, on just my second track day with the Big Brake Kit (BBK), I improved my best lap time by 4.445 seconds to 1:51.508. TrackAddict calculated a theoretical best lap of 1:49.611 and I was looking forward to seeing a a 1:49.something lap this day.
Instead, my tires felt slippery and in the fourth lap of the day I spun coming out of Turn 2 and ended up backing into the dirt on the inside of the turn. The next full lap, I felt the onset of another spin at the same spot but caught it before going off again. Then, black flags came out for everyone and I soon found that someone had rolled his Hyundai Veloster at the top of The Corkscrew.
All of this provided an ignominious start to the day.
The wreck cancelled session 2 for my group so it was over three hours before I was back on the track, by which time everything had cooled and I was starting over. I didn't see a single lap below 2:00 during session 3, and only one during session 4—with slippery tires I was slow, which meant I was constantly letting faster cars pass. For the final session, session 5, I asked to move down to the next-slowest group, which finally allowed me to log eight laps below 2:00, including my best lap of the day.
The next-to-last hot lap of the day was my best. At 1:55.664, it was more than four seconds slower than my best in March, a huge disappointment.
This was my second track day with Bridgestone Potenza RE-71R tires. On their first outing, at Thunderhill (West) seven weeks earlier, these tires felt good. Not as sticky as the previous Nitto NT01 tires but capable, and I improved my best lap by over nine seconds.
Why the tires were so awful this day was a puzzle, and led to me cancelling my next track day (and visiting with my Volkswagen Cabriolet instead). Three theories developed:
One theory was that the improvement at Thunderhill was illusory since my previous best came from an abridged day in June 2020. That was my first experience with that track and provided a poor baseline as worn tires and extreme heat curtailed the day after just two sessions. A big improvement over that day was expected.
On the other hand, several comparisons suggest that Thunderhill (West) was indeed a good day: I was about four seconds faster than several friends with Miatas, who I had expected to be competitive, and my 1:33.132 lap was very good compared to friends from an earlier analysis.
Several friends suggested that my tire pressures were too high, but only after the very last session (with my best lap time) did one tire exceed 38 PSI (table below) whereas they peaked at 40.5 PSI at Thunderhill after multiple laps yet didn't seem especially slippery.
I routinely see pressure swings of 8+ PSI over the course of a 20-minute session. If I target a reasonable hot pressure, I need to start with a cold pressure that causes unsafe rollover and sidewall damage (and accompanying TPMS complaints) for up to half the session, as I expereinced at Willow Springs in February. When there is a long dwell time between sessions (more than 40 minutes), half of every session ends up being spent warming up tires. That's nuts.
Although my previous Nitto NT01 tires wore quickly, they handled moderate overinflation well. Given the wild pressure changes I experience, these will probably be my next track tires.
Yet another theory was that the Bridgestone tires don't like being cold. Ambient temperatures at Thunderhill had reached 100°F whereas at Laguna Seca they only briefly topped 70°F. This idea makes the most sense to me, but similar temperatures at Thunderhill in October didn't provoke such slippery behavior.
Several people suggested that RE-71R tires are great for autocrosses but that they fade quickly over the longer duration of a track session.
The following table summarizes tire pressures throughout the day:
Description Time Ambient LF RF RR LR Note before session 1 0747 57°F 37 37 36 37 31 31 31 31 reset after session 1 0919 57°F 37 36.5 35 34.5 before session 3 1234 71°F 32 32 32 32.5 after session 3 1315 69°F 38 38 37 36.5 before session 4 1416 69°F 33.5 33 33 33 31 31 31 31 reset after session 4 1454 68°F 36 36 35.5 34 before session 5 1622 68°F 31.5 31 31.5 31 31 31 31 31 reset after session 5 1657 66°F 38 39 35 34 Chevron 1938 64°F 30 30 30.5 31 35 35 34 34 reset
Below 31 PSI, TPMS starts complaining. That in itself isn't necessarily a problem, but as noted above that paralleled horrible rollover and sidewall damage in February. As seen in this table, even starting session 5 with tires at a minimal 31 PSI, the front tires were over an ideal 36 PSI after the session.
Assuming the tires were at ambient temperature before session 5, the first law of thermodynamics says the right front tire was at about 204°F by the end of the session. Perhaps tire blankets or even tire warmers would help reduce the heat-induced pressure changes.
Understeer had long been a problem for me in the exit of Turn 2 (The Andretti Hairpin), leading me to a hook-like line rather than a double apex. Some upgrades earlier this year led to a better line and minimal understeer.
A spin, which is essentially oversteer gone wild, was the last thing that I expected at this point but that's what happened on the fourth lap of the day. The next lap included a quick visit to the pits after the expected black flag, then during the next hot lap another spin started at the same spot, though I caught it that time. The video shows both events.
At the onset of the second event I can't say exactly what I felt but think that I sensed the car not going where I wanted, a combination of expectation and newly learned instinct. The logical reaction would be to steer into the turn and, with a front-wheel-drive car, add power to pull out, but studying the video I can see that wasn't the case: the video from Greg Epstein, who was follwing me, shows that I steered slightly away from the spin. The data from my own car, included in the video that I recorded, shows that throttle position was constant and not increased until I was out of the turn.
Cooked brakes have been a problem on the track throughout my ownershop of this car. I finally installed cooling ducts for the front brakes. These ducts take in cool air using the openings intended for fog lights, and since those lights have become dark holes I've dubbed them fog darks.
This was their first track outing, but between tire problems and a damp
start to the day I didn't have an opportunity to explore the benefits
of this improvement.
This video (MPEG-4 version) shows my spin at Laguna Seca's Turn 2 and a subsequent incipient turn from which I recovered.
Like many people, I drive these track days for fun, but learning how to
control our cars when things go wrong is more important in the grand scheme
of things. This was one of (er, several of) those moments.
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Copyright © 2021 Karl L. Swartz. All rights reserved. |
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