Our last experience with traction, tires, and track.
Our last JF Heritage race in Sacramento we had some bad tire shake, enough so we had to weld up a cross member just in front of the fuel tank, and more important we twisted our rear axles and could not get replacements in time to race the Div 7 race this past week-end in Sonoma. We know it was tite shake because just before going to Sac, we changed rear gears and the axles looked great, but after the race where we shook so bad we crossed the center line, too bad too because Matt, our driver had a great hole shot.
Now I might have been able to make a last minute change if had been a liitle smarter, the run just in front of us in the same lane was Don Enriquez had the worst tire shake . So I should have had our crew quickly lowered the tire pressure 1/2 lb [ on my 33x12x15 GY] to increase tire spin [ to 5 1/2 lb] , instead of dead hooking and tire shake. The track was real sticky on the start line [ I had to fight walking out of my shoes].
The track ran jet cars before JF raced , and I think the track might have over prepped the track [ a bit too much VHT], after running the jet cars.
I just talked to a JF car that just raced Sonoma, and he had tire shake too, and at Goodyears suggestion, he kept raising the pressure to 7lb on his 31x12x15 Goodyears, there-by making the sidewall stiffer, but he still had tire shake. All this lower-raise pressure is confusing because my experience has been , with no bead locks, if I'm looking for more traction [ less tire speed] I raised the pressure to get the tire flatter across the tread, and if I'm looking for more tire speed I lower the pressure, and that concaves the center of the tire , there by the traction is running more on the edges of the tire.
To confirm that idea after the run I run my infared temp gun across the tread and see that the tread is hotter at the edges, and cooler in the middle. The reason we want more tire speed is to make sure the tires doesn't get too much traction and pull the engine down below the HP/RPM range. My GY guy also suggested I should have lowered to pressure after seeing Enriquez tire shake, and he also is seeing more tracks over prepping the tracks.
We may have to try smaller tires, but I have tried 33x10.5x15 MT but they didn't run as good an ET, but better 60' times. THe 10.5 door car tires have stiffer sidewalls and don't grow with speed like the 31x12x15 GY.
Feedback is invited.
Jon
