"Mr. Toad" at Laguna Seca (29 March 2021)"Mr. Toad" at Laguna Seca (29 March 2021)
 Turn 6 |
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Proper attire adds horsepower and thus speed.
 Sea otter mask for sea otter territory |
 Finish-flag socks from my sister |
Greg Epstein finished off a set of EBC YellowStuff front brake pads by mid-morning. (They already had a few track days on them; even I can't destroy brake pads in less than an hour of track time.) Fortunately, he brought spares so didn't even miss a full session.
 Banana-peel traffic "cones"— Orange thing is the state tree of Illinois. |
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| This new Lotus Evora encountered "slippery" coming out of Turn 11. Here's the dashcam video of the impact. |
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 911, auf Deutsch (sort of) |
 "Love Nurburgring" |
 Mini Cooper = XX SMALL |
 Muahahaha Miata? |
With a package of upgrades from last month, most significantly the Big Brake Kit (BBK), my goal was to beat my previous best lap time of 1:55.850, established last August, by four seconds. My stretch goal was to improve by six seconds.
Details are below but the four-second goal was met during the second session of the morning, a remarkable improvement. Alas, pesky traffic in the afternoon held me back from the six-second stretch goal and a lap time below 1:50.
Two months before this track day I learned that my Big Brake Kit (BBK)
would not arrive until early April, a week too late. That resulted in me
planning around cooked brakes. Fortunately, a
surprise delivery notifaction from UPS in mid-February portended a happy
early delivery of the new brakes, which worked wonderfully last month
at The Streets of Willow Springs—and
again at Laguna Seca! I seriously doubt any of my attempts at hacking things
with the stock brake calipers would have resulted in anything beyond more
boiled brake fluid and fried brake pads.
 Short-lived new record (1:53.853) |
 Best lap of the day (1:51.508) |
 Best afternoon lap (1:52.226) |
During the first session I warm up tires and brakes and remind myself how to drive the track. After three laps, I woke up and realized that I had fallen into an old profile of downshifting to 3rd gear before The Corkscrew, a problem repeated from February 2020. Finally remaining in 4th gear at that point, which I had figured out was best nearly two years ago, speeds picked up, and I ended up shaving almost two seconds off my best lap time—1:53.853 in lap 7.
The second session saw my four-second target improvement, to 1:51.796 in lap 3. The third and last session of the morning saw my best lap time of the day, 1:51.508 in lap 7, a 4.445-second improvement over last August.
During the four afternoon sessions at least a few drivers jumped from
other groups, leading to a track crowded with heavy, slow traffic, which
got in the way of further improvement. My best lap of the afternoon was
the last lap of the day,
1:52.226 in lap 4,
at the end of a session abridged by a broken car from the previous group
which needed to be recovered.
Looking at the above lap images from TrackAddict you'll notice some serious "farming" expeditions—major off-track excursions into the dirt. During my best lap, it looks like I made hard right at the exit of Turn 9 (below left), then banged across the exit of Turn 10 at a nearly 90-degree angle and almost into the paddock before getting back on course at 91.1 mph. I'm pretty sure I would have remembered all of that.
 Session 3 Lap 7 from Turn 9 |
 Session 7 Lap 4 from Turn 5 |
Similarly, at the end of the afternoon, I apparently came out of Turn 5 at 51.9 mph (above right) and then climbed the hill up to the entry roadway south of the track before jumping down and flying under the bridge into the paddock at 93.6 mph. Earlier in that lap, I took Turn 2 (The Andretti Hairpin) at just 35.7 mph yet accelerated to 80.4 mph before the next turn.
Greg Epstein had previously complained about this phenomenon but it was new to me. Two things changed for me: I upgraded from an iPhone XS to an iPhone 12 mini, and with that hardware upgrade I went from iOS 12.4 to iOS 14.2. It seems probable that Apple introduced a regression and failed to catch it in QA, probably in the software since other friends are seeing the same problem on different hardware.
Lap times are still credible since TrackAddict clearly has a good idea of where the start/finish line is, as demonstrated by an imaginary farming expedition that missed the start/finish line by a wide margin and resulted in two laps being conflated into one. However, speeds at various points are not trustworthy as exemplified by the screwy speed in Turn 2 in the day's last lap. (TrackAddict can use the car's notion of speed but this has its own issues, in my case because I upgraded to larger tires which should introduce a speedometer error of about 1.27%, but also because tire wear and inflation can influence the indicated speed, as can spin and other issues.)
The solution seems to be to buy an external, high-resolution GPS receiver. I'd really rather spend the money on going faster rather than measuring faster!
Although the speed data is suspect, there were multiple laps where TrackAddict showed the top speed (just past Turn 1, at the end of the front straight) as being 112 mph, ±0.1 mph. That's plausible and a significant improvement over 109.7 mph from last October. This is exactly what I expected, with the BBK allowing me to keep accelerating all the way to the #3 braking marker for Turn 2 before braking HARD. A friend who followed me for a bit in his Lotus wondered if I was ever going to brake, and then laughed at my car's little dance as nearly all the weight transferred onto the front wheels and the rear tires scrabbled for traction.
By mid-afternoon, I began noticing some vibration under heavy braking starting about midway through each session, i.e., after the brakes had gotten hot again. It tended to be most apparent braking for Turn 10, and oddly not noticeable braking for Turn 2 which is the hardest braking on the track. It had the feel of a warped rotor, or possibly an out-of-balance wheel though I wouldn't expect a wheel to be heat-sensitive.
One suggestion was that pad deposits on the rotor might be the cause, and there was some evidence of that, but the big problem turned out to be that the inner left pad had cracked (see photographs below) and all of the pads along with the rotor showed signs of intense heat. Until replacement pads arrive I'm using StopTech stock, street pads. This answered a question about using the G-LOC R16 pads on the street since their operating range starts at 123 C / 255°F: even cold, they far outperform the StopTech pads.
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I'm getting better at managing tire pressures though it's not easy. The stickier Nitto NT01 tires seem to handle over-inflation better, making it possible to start a session with pressure high enough to not trigger Tire Pressure Monitoring System (TPMS) warnings and yet not end the session on ice skates.
The following table summarizes tire pressures throughout the day:
Description Time Ambient LF RF RR LR Note before session 1 0756 41°F 36 36 35 34.5 33 33 33 33 reset after session 1 0943 52°F 44 45 39.5 39 40 40 38 38 reset before session 2 1011 52°F 35.5 36 36 35.5 after session 2 1045 54°F 40 40.5 38 38 39 39 - - reset after session 3 1146 56°F 39.5 40 38 38 before session 4 1309 56°F 34 32 36 35.5 after session 4 1344 57°F 36.5 36.5 36 36 - - 35 35 reset after session 5 1443 56°F 37.5 38 36 36 after session 6 1545 56°F 36.5 37 36 35.5 after session 7 1645 54°F 36 36.5 36 35.5 Chevron 1815 55°F 30.5 30 32 32
At Laguna Seca, the right front tire takes the worst beating and during the first session that tire gained 12 PSI. Assuming the volume of air in the tire remains constant—a simplification since higher pressure does cause the tire to balloon somewhat—allows this to be viewed as an isochoric process. Applying the first law of thermodynamics with this simplification, the relationship between temperature and pressure changes is as follows:
P1 / T1 = P2 / T2
The ambient temperature increased from 41°F to 52°F but that only accounts for an increase of about 0.7 PSI. The 12-PSI increase indicates the air temerature inside the tire increased to about 284°F, due to a combination of the tire heating (due to friction with the track and flexing of the rubber) and brake heat entering through the wheel. Planned brake-cooling ducts may help somewhat, and insulating blankets for the tires for use in the paddock may help reduce wild tire-pressure changes. (Calculations require that the temperatures be converted to Kelvin—or Rankine if you're weird.)
The Nitto NT01 tires were wonderfully sticky but after just two track days they are close to being slicks. The photograph at right shows one of the front tires, which weren't quite as worn as the rear tires. The sides still exhibit plenty of vent spews, otherwise known as rubber hairs, but there's not much left of the tread. (The rear tires were down to 2/32" afterwards.)
I should be able to get at least one more track day out of them. After that, they'll be slicks, which is ok for the track and in California's dry season, though bare cords may not be far away.
In February 2020, I worked on a hook (or diamond) line through Turn 2, going deep and only hitting the second apex in order to minimize understeer coming out of the turn. With the upgraded rear swaybar and better tires, I had banished understeer at Willow Springs last month, and hoped to demonstrate the same improved behavior at Laguna Seca. That expectation panned out, allowing me to drive something closer to the preferred double-apex line, though carrying as much speed as possible off the front straight I didn't quite hit the first apex. It still felt much smoother and speeds in this turn appeared to increase.
Turn 6 has long been a challenge for me, and watching video of me following Greg in his MINI Cooper (right) reinforced just how much I'm giving up in that turn. Yes, like a Miata, a MINI Cooper is more nimble than my Mazdaspeed, but my car was also held back my poor meatware at the helm. This is undoubtedly my weakest turn at Laguna Seca.
The video excerpt at right shows this dramatic difference, even though I soon used the Mazdaspeed's raw power to catch up again.
Greg followed me for a few laps and commented on my line through several turns. One was Turn 7, where he noted that I could stay much farther right, going deep into the green verge, almost eliminating the turn to allow a faster line with braking after the crest before diving into The Corkscrew. That was far better except for the braking—even with the mighty BBK I needed to brake some just before Turn 7, though most of the braking came after that.
Harking back to February 2020 again, I had worked on a tight exit from Turn 8a. There's a rectangular patch in the pavement that I would straddle, a convenient reference point. This time I found myself staying to the right of that patch, taking advantage of the improved tires and perhaps the stiffer rear swaybar to set up better for the entry to Turn 9.
The photograph below shows me relative to that patch, along with Greg in his MINI Cooper following an even wider line than I used to use.
Turn 8 exit line comparison
Oddly, although Turn 9 has long been my best turn on the track and a tool for beating much faster cars, this day I felt that I was just a bit off, not really using all that my car could do. I'll work on that next time.
Looking back, this was a wildly uncontrolled experiment, which rankles my scientific mindset even if I was thrilled with the results. There were at least six significant changes in my car:
Beyond the hardware changes, drastically reduced understeer (due to the RSB and possibly also better tires) led to a different line through Turn 2. I should try a few laps with the old line through that turn for comparison.
The poor data further compounded the challenge
of understanding what helped, and what perhaps didn't help. I'm eager to go
back and, er, collect more data!
This video (MPEG-4 version) is from the three morning sessions. Usually, the number of cars that pass me and that I pass are about the same but in these three sessions NOBODY passed me.
This video features lots of passing action, plus my best lap. The best lap starts at 10:50 if you just want to watch that, or skip to any of these points:
This video (MPEG-4 version) features several laps from session 6 with me following Greg Epstein in his 2014 MINI Cooper S. I'm generally several seconds faster but we knew there would be lots of traffic so I just followed for a while. That let us get video of each other, with him using a GoPro on his rear bumper to record me, an interesting and educational perspective.
His bumper cam video is superimposed in the
upper left corner of my video, which has the usual data from TrackAddict.
Although our devices didn't record synchronized times I used various
visual clues to synchronize the videos to within a fraction of a second.
This video
was taken by Greg Epstein in his 2014 MINI Cooper S using a
backward-facing GoPro on his rear bumper, with me following.
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Copyright © 2021 Karl L. Swartz. All rights reserved. |
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