We've recently changed over to stiff sidewalls. Only did 3 passes before hurting the motor but I can tell the car did not like 11.5 psi in them (on my gauge). Car squirmed around a lot from the startline. We started @ 12.5 and went down. Next time out we'll start there and go up, tyre was wadding pretty bad in hindsight. Got a 1.41 60ft but track wasn't there, so everyone was saying, so it sorta equalled the non stiff wall slicks given the conditions. I think the normal slicks are a bit more forgiving when it comes to pressure.
We still run ours with tubes too, is this right?