Depends on wether you are looking for that slight harder or softer ride and also if you are willing to sacrifice a lil extra tire wear. Around 40 psi plus or minus a few for a harder ride, around 30 or a lil more for a softer ride. I forgot which causes a slighty faster wear but i guess it's all about that sidewall flexing because that's what absorbs majority of the road condition. Being 40 series tires though, i don't think it really matters cause you don't have that much sidewall...around 40 psi is the ideal pressure you should have in your tires....