I'd start at 13.5-14 and work your way up till it spin's I run a 28x11.5 and run as much as 15 on a cool day if needed (I adjust rear tires for reaction time) and my car probably weigh's in at 3300-3400 w/ me..... low air pressure does nothing but kill the sidewall's and slow you down!!! my car will hook on anything....if I'm in the grove LOL

Andrew Brough D372 1969 Dodge Dart GTS 1.43 60'best 6.82 1/8 98mph "the light came on and I ran out of talent"