Eagle 1 Nascar tires

I have eagle 1 nascars on my camaro, but i have had difficulties determining how much psi i should have in them.. They were at first 40 psi, but that is way to high so i dropped them down to around 30 psi each, is that a good psi for this car/tire combination? or should i change it?

id go w/ 32-33 psi, for ideal handeling, ride comfort, gas mileae, etc. But ask Grant, from tirerack.com