"Mr. Toad" at Thunderhill (24 September 2020)"Mr. Toad" at Thunderhill (24 September 2020)
 Two very different sorts of track vehicles comparing numbers. |
 Pink bubbles replacing Valley Vermin (insects) |
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 That pink bubble bath didn't last long |
| Black Mazdas ... | |
 Ready to go! |
 Fueled, emptied, numbered, and ready to rock. |
 A friend gets some helping hands |
Plans changed when during the last group of the second session someone destroyed a BMW M3 (E92) at Turn 9, flipping it end over end. The driver and passenger departed to Santa Rosa via helicopter but apparently didn't even suffer any broken bones. Their automobile did an amazing job of protecting them.
The crash resulted in just two sessions in the normal direction, with an early lunch followed by five sessions in the reverse (clockwise) direction.
My previous fastest lap recorded on Thunderhill's east ciruit was 2:30.004 one year earlier; top speed on the front straight was 103.8 mph. (I probably had a better time during the last session but Track Addict got into the wrong mode so I didn't collect any data from that session.)
During the first morning session, focused on warming up tires and brakes, plus exploring the new behavior of the car, I still knocked off over five seconds versus my previous best time with a lap time of 2:24.951.
I went into the second session having bled off 3.5-5 PSI of air pressure from the front tires, and 2 PSI from the rear, and knocked almost 5.5 seconds off my first-session best time, for a best lap time of 2:19.456, 10.548 seconds better than my previous best. With two more sessions I might have shaved off as much as another second or two.
One surprise was that the new power curve didn't dramatically alter shift
points. The only significant difference was that the upshift from 4th to 5th
on the front straight came a little later (since the engine now maintained
power into high revs), with a top speed 1.4 mph
faster. I had thought I might not even need 5th gear there, since slightly
faster speeds at Laguna Seca were ok in 4th gear, but without the slight
crest at Laguna Seca's Turn 1 the upshift worked
better on Thunderhill's front straight.
 Best lap of the first clockwise session |
 Best clockwise lap (Session 7) |
 111.7 mph! |
My first reaction to driving the track "backwards" after lunch was that it was weird and uncomfortable, even a bit disturbing. More turns were blind, including the Turn 5 bypass.
As the afternoon progressed, I grew more comfortable and lap times steadily decreased until in the last session I was less than 2.5 seconds off my (newly established) best time in the normal direction. Here are the best times from each session:
Session Best Lap Delta Fastest
(mph)3 2:52.109 - 105.7 4 2:32.902 -19.207 110.7 5 2:27.746 -5.156 110.3 6 2:23.840 -3.906 111.1 7 2:21.854 -1.986 111.7
The fastest speed was at the end of the front straight and was a function of three components: a good exit from Turn 1, braking as late as possible for Turn 15, and then taking that turn as fast as possible. These steps were straightforward so it's not surprising that speeds here quickly approached their limit—the 30+ second improvement in lap times came from big improvements on key turns between the first and last sessions of the afternoon..
Session Best Lap Turn 10 Turn 9 Run 8-7 Run 7-6 Turn 5
bypass3 2:52.109 41.3 45.1 83.3 77.1 51.6 7 2:21.854 53.3 55.8 92.3 91.8 69.0 -18% +29% +24% +10.8% +19% +34%
Turn 10 is critical because it leads
to a relatively long, uphill stretch—about
1,500 ft (455 m)—to
the entrance of Turn 9.
Turn 9 itself took some work because the approach
is blind and at the crest of a hill, leaving the car unsettled just before
braking and then turning. It turned out to be a fast turn, leading into a
fast pair of turns at the north end of the track and a significantly
faster run after Turn 7.
Turn 5 bypass
Running clockwise, the Turn 5 bypass is not only blind but has enough of a crest to cause some cars to become airborne. We had been warned to expect this and while there was little enough weight on the wheels to elicit a chirp when traction was re-established photographs (see right) didn't show any light underneath my tires, just a car riding very high on its wheels as if it were a crossover.
Add in needing to know where to aim since you couldn't see the twist beyond and the corner was a wild ride. Maximizing speed here was dependent upon learning where to set up for what lies beyond, then doing so and hanging on.
The second picture at right shows the view from inside the car, with a BMW Z4 cresting the hill ahead of me to offer an idea of what is to come. As noted, we drove the bypass of Turn 5 (The Cyclone), which is off to the left but blocked off by the orange cones.
Track Addict, the iPhone app that I use for collecting data and recording video from my track adventures, has track definitions for Thunderhill East, West, and Full. There is also a B version of Thunderhill East, though it seems to have disappeared. It was unclear what the B version was until I looked at the map: it uses the bypass of Turn 5.
All are for the normal direction, however, and the app got very confused
when running clockwise, thinking I must still have been in the pits until
nearly one full lap, when I finally passed the start/finish line. The
six sector definitions were confused, too, with the first four registering
no data at all. Sector 5 was from start/finish
through the straights surrounding the pits to Turn 13.
Everything else was sector 6, as seen at left.
This time, Josh Bligh and his 2017 Shelby Mustang GT350 was in the same group as me so we had several chances to spar. During the reverse runs in the afternoon he caught up with me; the photograph at left shows him hot in pursuit coming out of Turn 14 onto the back straight during the reverse afternoon. With nearly twice as much horsepower he was faster but didn't get past without a fight.
Greg Epstein was in a different group, plus his 2014 MINI Cooper S was awaiting new brakes, so he drove his Tesla Model 3 Performance instead (when not looking for a Supercharger). We were in different groups so didn't get to compete directly but he and Josh were in the same group for one session and Dito Milian captured them in Turn 13, with an Alfa Romeo hot on their tails.
MINI Coopers tend to be a good match for my Mazdaspeed, slightly more nimble
but not quite as powerful, as I experienced from the driver's seat
at Harris Hill last year
and in friendly sparring with MINIs at California tracks. Greg and I are
looking forward to trading cars for a session at a future track day.
Braking was a big concern after my
incinerated brakes at Laguna Seca
last month. Although speeds were faster in the front straight, the turn at
the end was much faster. Worst case was in my fastest afternoon lap, which hit
111.4 mph on the front straight, slowing to
59.7 mph at the entrance to
Turn 15. That's an energy dissipation of about
1,390 Joules, 13% less than coming off the front
straight into the Andretti Hairpin at Laguna Seca. That's still a
lot of energy to be dumping but apparently enough less to stay below what the
brake pads could absorb without damage as there was no brake fade and the pads
still looked good at the end of the day, with traces of heat but nothing
resembling the inferno seen at Laguna Seca.
This video (QuickTime version) shows the last three laps of the day, laps 5 through 7 of the last session, Session 7.
At the start of the video, I catch up with a Mazda Miata and then pass after Turn 14. Slowly, I then caught up with a BMW Z4. We both passed a Subaru after Turn 2.
Lap 6 was my fastest lap running clockwise at 2:21.854. During this lap I kept up with the Z4 but didn't manage to pass him. In a few places, observing his lines helped me fine tune my own. Afterwards, he expressed surprise that I was able to catch up with him and stayed pretty close even in the turns, where the lighter and lower Z4 has an advantage.
At the beginning of Lap 7 we got the checker flag to mark the end of the day but passed another Miata, the Z4 doing so on the front straight and then I got my chance after Turn 14.
This video (MPEG-4 version) is from Josh Bligh in his 2017 Shelby Mustang GT350, chasing me during during the second clockwise session (Session 4 of the day). At this point both of us were still figuring out how to drive the course clockwise and was early in the afternoon's progression of steady improvement. My line through Turns 9 and 8 was notably sloppy, well off the apex and exit. A better line by the last session led to a 8.8% speed improvement through Turn 9, and a 7.5% improvement in the straight between Turns 8 and 7. The improvement after the Turn 5 bypass was even more dramatic at 16.8%, from 59.1 mph in Session 4 to 69.0 mph in Session 7.
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Copyright © 2020-2021 Karl L. Swartz. All rights reserved. |
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