Putting on lower profile tires than stock means you have to increase tire pressure from the door jam-listed 30 psi?

I figure my move from a 16" wheel to an 18" in the rear (with the same tire height) must require some compensation for the fact that it has less cushion between the rim and the road. Am I wrong in this assumption?

The standard "run 32-35 psi" answer can't apply the same to all wheel sizes can it? In my mind, larger tire profile allows the tire room to flex more so you can use a softer psi like 30.

 

My stock 245/50/16's I ran 30-32 My new 18's I still run 30-32. I would keep the pressure between 30-35 any more then that will cause the tire to wear unevenly and the ride will suffer. JMO

 

It is pretty complicated- you have the tire manufacturer's range, the vehicle manufacturer's range- and what is right for your application. Typically, with a front engine car, the fronts should have a couple PSI's more in them than the rears, unless you are carrying a heavy load.

The 'correct' way to do it is to set your approximate pressure, drive at typical speeds, and measure the tread temperature across the whole tread face- you need a pressure that equalizes the pressure, and temps, across the tread- Most people don't have the equipment or inclination to be so precise- other than racers. Drive a while and monitor tread wear patterns, and make your adjustments accordingly-

One final aside: when you go to a wider tire, you change the tire footprint shape- the weight of the car stays the same, and you need a similar PSI to support the weight of the car, which hasn't changed- if the tire patch gets wider, it must get shorter to have the same number of square inches (at so many PSI's) against the ground-

 

I always set pressure according to what's on the tire, not the door jam.

 

I go off the tire too. I usually start with 40 and work down from there depending on tire wear and feel.

you got a really good answer earlier.

 

That went way over my head. LOL