Originally Posted by enigma
Lets just say your data and my data disagree....
The reason people don't run a MPSC at autocross is because of temp issues. You cannot get the tire hot under normal autocross conditions.
Pinching a tire, running too wide for the rim, generally doesn't generate more grip. However, this varries from tire to tire and hoosiers generally handle this better than most, because in part they are designed to run on narrower rims. However, for everything there are limits and 265 on 8.5" is really close. You have to think about what happens to a tire when the sidewall deflect during cornering.
Hoosiers are not 4s faster than PS2s on a 60 second course. There will also be variations dependant on surface conditions.
I agree on the MPSC and temp issues only when running on cold weather. On summer conditions, they're good on the second lap, I ran MPSC for three years.
At National level, the top cars/drivers are running wide tires on narrow wheels in all the stock classes. The 275 A6 works well with a 8.5" wheel, National top level Soltices are running 285 with shorter sidewalls on 8.5". I trust the experience from the highest level autocrossers in the country. V710/A6 allow this due to stiff sidewalls, the same cannot or should not be done with standard street tires.
If you cannot drop 4 secs between wider A6 and stock PS2 at an autocross (using a 60 secs course as a baseline), you might be under driving the A6. This is not applicable in the rain, so it is definitely surface condition dependent.