An Autocross Season-Part 13: 2nd In Peru

Silver Ghost got a good 2-day shakedown with myself and a co-driver on the new set of tires at our local Tour de Frank event (Milton Frank Stadium) the weekend before Peru. It didn’t start well.

The new tires consisted of 265mm Yokohama A052s on the front in place of the original 275mm Falken 660’s. In the rear I had a new pair of 305mm Falken 660s, just like before. I had previously driven the car around in circles to give the tires an initial heat cycle and then let them sit for 24 hrs before using them again.

There was a shocking lack of grip from the new front tires, causing us to miss all our braking points, plowing through walls of cones, and to understeer terribly and miss our apexes.

At the time I bought this second set of tires for the year the 275mm Falken was not available. Lots of tire shortages going around.

My co-driver and I found we had to massively lower the tire pressures. This, plus several runs, seemed to bring the Yoks into frame. By the time we had 6 or 8 runs on them and 4 less psi all around the car was much better, though it still understeered. I set it down to the supposedly common knowledge that Yoks do not like to be pinched while Falkens are much more tolerant to over-tiring the rim. (However, I had used this same tire on the exact same size rim on the C5 and it was fine.) I was able to place 6th of 19 in Pro class both days (7th of 98 overall) while still having extreme difficulty with understeer and poor braking into corners on the bumpy entrances to several key corners. Ryan T. from down the road in Birmingham was in his new B-Street Supra and placed ahead of me in 5th in Pro each day. I would be against Ryan at Peru and I now put him down as the tentative favorite, though I had little knowledge of the competitors we would face.

Loaded Up For Peru, Indiana and Grissom Airport

Fearing more understeer at Peru I softened the front bar to the middle setting from full stiff. On the practice course on Friday I ran 2 psi more pressure than at Tour de Frank, trying to prevent too much tire rollover on the higher grip surface. The car understeered but it did brake well on the smooth concrete, confirming that the car is just too stiffly damped at 90% critical* and high gas pressure for the bumpy Milton Frank surface.

I then reset the front bar to full soft and added 3 sweeps of compression to the rear shocks in an attempt to move the corner entry balance more toward oversteer and went back out for a few more practice runs. The car seemed better. Boy, did I have it wrong.

When it came to the higher speeds on the real course the car understeered badly into the corners and now power-oversteered out of the corners given any significant throttle, something it had never done before. I had to drive very timidly. When I looked at the standings for the first time after the first two runs I was in 4th of 8 drivers, a tenth away from 3rd, the final trophy position, and a half-second out of 2nd. (2nd and 3rd places were held by co-drivers of another Supra.) Ryan was in the lead in his own Supra.

In desperation I dropped the tire pressures down to exactly what we had used at low-grip Milton Frank and took the 3 sweeps of compression out of the rear shocks. I was able to push more on the final run. I went considerably faster and ended the day very slightly out of third and two tenths back from second. Ryan had a screaming 3rd run and left the rest of the class in his rear-view.

On day 2 I made no further changes and gained confidence and speed on each run. Even so, after two runs I looked at the standings and the driver in second place had put another two tenths on me, so I was now down by 4 tenths, but at least I’d taken over 3rd.

On my last run I got the clean four tenths I needed and edged into 2nd place by a few hundredths. The Supra driver had his last run remaining and only needed a very slight improvement to retake 2nd, but I was hoping I had put a little pressure on him, assuming he even looked at the standings or cared. I watched his first section. It looked faster to me than his previous run. I watched his second section. It was definitely faster. When he crossed the line the display showed a time plenty fast to beat me. Then it was announced that he had coned the run in what I’m calling the second section. I took the trophy for 2nd place.

After banking a couple of conservative, clean runs Ryan blitzed his 3rd and absolutely smoked the class, a well-deserved first Tour win for him. I guarantee it will not be his last. He used to race dirt tracks. That boy can boogie.

Peru B-Street Finishing Positions

My co-driver and I have one local event before going to Bristol for the back-to-back Pro and Tour events in July. Bristol has bumps and weird slants and dips and cambers. Too stiff and you’re likely to fly off into the creek that snakes through the property. (There’s a nice, cool swimming hole, too.) We have a testing strategy planned for the local. Hopefully, we can figure some things out and get this car (and the drivers) dialed in.

*In Part 14 I explain that I discovered the shocks were actually at about 108%critical, not 90%, as I thought.

2 thoughts on “An Autocross Season-Part 13: 2nd In Peru

  1. I tried the Yoks on the front of the Z4 knowing as you did that they don’t like pinch or lack of camber. Setup was 255/35R18 on an 8″ rim, with -1.1 degree of camber. With that setup they were super sensitive to pressure. Even the pressure change during a run seemed to move them out of their better zone. I say better because I never found anything I could call their truly happy zone. 😦 Seemed I could choose a good first part of the run with them falling off on the latter, or not as good starting out and have them come in for the finish. They were slightly better than the RE71s in the same fitment, but that was an amalgam of noticeably better during part of the run and maybe about same/slightly worse for the other part. The RT660s in same fitment didn’t show quite as much peak grip as the Yoks, but they were consistent through an entire run and as such were faster. On my MR2 with just a bit of pinch and >-2 degrees of camber all around they’ve been really good and not too difficult to find an optimum pressure. Now just dealing with trying to keep them cool enough run to run. Hope you’re able to find a good setup with them!

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    • Thanks for the information and encouragement. I have plenty of front camber (min of 2.6 deg) and I spray after every run, even with no co-driver, knowing well to never let them get hot. I plan to go back to the Falken and optimize solely for that tire.

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