How do you determine the correct tire pressure?

I recently asked a question which thankfully a fellow board member was able to answer for me since he works for Toyo and was able to tell me the proper tire pressure for my 18" T1R's. But say you don't have access to such a person and you change your wheels and tires from the stock size and speed rating. How are you to know what new tire pressure you are supposed to be running? Manufacturers don't really help since they tell you to run it at the same pressure the original wheels had. This is only true if the replacement tires are the same size as the originals. So, how do you know? Thanks

Your tire should have a max pressure number on the sidewall somewhere. As long as you don't exceed that, and keep it away from the low tire pressures, then you should be fine. After that its just a matter of where you want the tire pressure to be.

For example, most of the tires I have had in the past say max tire pressre 44 psi. I usually run them with 35 psi on the street, and maybe drop them to 25 or so for the track.

But the max tire pressure is based on the weight of the vehicle and load per tire. The max psi listed on the tires is 50 psi cold. I am probably going to run them at 38 psi. Thanks for the info.

You have a good point. Sometimes it's hit or miss with the tire pressure. I've had to watch the tire wear in certain cases and adjust the pressure accordingly.