I run a Hoosier 29x14.5x15 and have best luck around 12-13psi. There are many variables including how heavy the car is and how the weight transfer is. I have run them as low as 10.5psi. In short you need to tune them in... change the tire pressure about 1psi on every run and look for your best 60'. A fellow racer told me if you see burnt rubber wrapping over the edge from the tread to the sidewall, the pressure is too low. You can run a shoe polish line across the tire and see where it wears off... you want it to wear evenly if the chalk stays in the middle the pressure is too low if it stays at the edges the pressure is too high... I think around 12psi will be a good starting point...

-Chris