What tire do you have? The size doesn't matter too much. It varies depending on the tire; some have softer sidewalls and tend to roll under during hard cornering. How aggressive do you corner? Check the max on the sidewall though and keep 8-10 below that for cold psi. Just adjust it 2psi at a time up from 32psi until you find a middle ground that you like for comfortable ride, gas mileage, wear, etc. Try a search also.
OBJunior said:
How do you know what pressure you should run your aftermarket tires at. I have 215/35R18 and I've been running between 30 and 40.
'Z' is the speed rating, meaning the tire has been tested to go higher than 149 mph (they do this so the lucky Germans know how fast they can drive on the autobahn). The speed rating has nothign to do with the pressure. Even when plus-sizing your tires, the best place to start is with the manufacturer recommended pressure (sticker on inside driver door jamb). DONT go any lower than that. You can go a little higher, but not higher than the max pressure listed on the tire sidewall. Increasing pressure will make your car ride harder and will probably cause the center of the tire to wear faster than normal.
