on my race cars (~1,500lbs to 2,400lbs) i use 30psi
on my oem cars (lambos, vipers, corvettes, mustangs, etc.) i use 34psi
yeaaaars ago i used to use the rule 10psi per 1,000pds, so on my sl-c i'd use like 22-24psi, but that's stupid for the street as it leaves minimal cushion room if something happens.