Quote:
Originally Posted by menncars
Slight bulge? Do you mean on one tire a bump appears on the sidewall? Or do you mean when all the tires heat up they appear 'fatter'?
I get the feeling you mean all the tires get a little fatter when heated up, which is normal. But if you get a bulge in the sidewall, get rid of that tire. It is possible the entire tread could separate from the rest of the tire if the bulge fails. Happens in parking lot? Sh*t. Happens on the track? Super Sh*t. You want to avoid Super Sh*t.
Looks like you've got the right idea with pressures. When I arrive at a track day I let the car sit for bit (15-20 mins or longer) then take tire pressure. Typically these numbers are around the mid 30s for a lot of BMWs on street tires. As soon as I return to the pits after the first session, I take the pressure again. Your intuition on pressure is the same conclusion I'd make. While tires can get as high as 50 (the max), for many street tires, past 40 PSI results in reduced performance. Repetition of 'too high PSI' may result in tire-i-cide, with one or more tires 'chunking'. Seems like you've been asking around about hot and cold pressures for similar tires and vehicles so you're on the right track. Getting a before track - after track reading will help you guage the numbers you need. As an example, I run the PS4S at 35 PSI on the street but at the track, I go as low as 29-30 PSI, 1 PSI about Ford Explorer roll-over pressures. Thankfully my fat-a$$ family sedan there heats up the tires pretty good.
Staggered is fine. Even in the solo group plenty of cars run staggered with some rear tires being akin to a small steamroller in size (I think the Viper ACR runs a 330 in the rear and 260 in the front which means more than 1 metre of rubber rolling over the road). You've likely heard staggered leads to understeer, which is true, but understeer can be reduced through other tweaks to the suspension. Or, you could turn earlier.
Sounds like you had fun. Looks like a repeat customer.
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Not only do the tires appear fatter but it seems uneven along the sidewalls. It's certainly not a "bulge" as I misidentified in my previous posts. I'll run around 35-36psi hot next time and see how that goes. One of the guys i ran with had an S3 and mentioned they had to run 40 psi since its low profile tires, he obviously aired down the lap after and had more grip.
I learned i could probably use the brakes a bit harder and turn in a bit sooner. The runflats feel like they're struggling hard for grip out of corners and on sweepers so I can't wait to go on something that grips more.
Hopefully the next HPDE will take place at Laguna Seca!