Tire pressure of bigger set-up than factory.

[Sotarts]

There's a recommendation for tire pressure for stock-sized wheels/tires.

But once we upgrade to larger diameter (17" specifically) wheels and lower profile tire, is there a rule to what tire pressure should be on a street driven car? For 215/50/17 and 225/45/17's? 1G AWD and 1G FWD?

 

[1LE]

Proper tire pressure depends more on the exact model tire you have than the size.

 

[Sotarts]

Originally posted by 1LE
Proper tire pressure depends more on the exact model tire you have than the size.

Enlighten me.

 

[1LE]

Hard for me to do. Tire construction is the big thing. Number and type of plies of sidewall and tread, internal design, etc. Either need to test and find the right pressure, or hopefully get some info out of the tire company. Stock pressure is usually a good place to start. First up, watch to make sure you aren't rolling it over onto the sidewall under hard cornering. If so, bump pressure up. Over time, watch/measure the tread wear. Wear in the middle more than edges, lower pressure. You may not find a perfect pressure. Adjusting pressure also allows you to mildly change the effective spring rate and feel of the car No simple answers here.

 

[Defiant]

eeeyeagh.

Tire pressure is somewhat equivalent to how much pressure in pounds per square inch your car is putting against the pavement (tire construction methods and other variables will keep this from being completely accurate).

So if you run the pressures indicated on the back of your driver's door, the tires compensate to a large degree, and there should be only slight differences from one tire size to the next, until you get into things like rubber compound and other stuff like tread patterns and even pavement texture.

You can do a _lot_ of handling tuning with varied tire pressures.

Up to a point, the harder you press, the better you hold..... within all the incalculable variables.

 

[1LE]

Far worse than "not completely accurate" I'm afraid to tell you. On one particular car of mine, with same size tires, 1 make of tire was best set to 32 front, 28 rear (ol' BFG R1). Comparable Toyo's of the time wanted almost 50psi front and rear to work right. Current generation Toyo's want 29 front and 33 rear for optimum performance...

"up to a point, the harder you press, the better you hold" is completely false. Lower tire pressures generally (with older toyo's being notable exceptions!) tend to give BETTER grip, however, you increase risk of rolling the tire off the rim...

 

[Defiant]

Originally posted by 1LE
Far worse than "not completely accurate" I'm afraid to tell you. On one particular car of mine, with same size tires, 1 make of tire was best set to 32 front, 28 rear (ol' BFG R1). Comparable Toyo's of the time wanted almost 50psi front and rear to work right. Current generation Toyo's want 29 front and 33 rear for optimum performance...

I had a similar situation when Michelin stopped producing the X-AS. They were magic on the roadster, and when they quit them, there was nothing else in the size (175-14) in the way of a performance tire.

"up to a point, the harder you press, the better you hold" is completely false. Lower tire pressures generally (with older toyo's being notable exceptions!) tend to give BETTER grip, however, you increase risk of rolling the tire off the rim...

Lower pressure will give a larger contact patch, but I'd think at some point there has to be a crossover between area and grip.

 

[Defiant]

Originally posted by 1LE
Far worse than "not completely accurate" I'm afraid to tell you. On one particular car of mine, with same size tires, 1 make of tire was best set to 32 front, 28 rear (ol' BFG R1). Comparable Toyo's of the time wanted almost 50psi front and rear to work right. Current generation Toyo's want 29 front and 33 rear for optimum performance...

I had a similar situation when Michelin stopped producing the X-AS. They were magic on the roadster, and when they quit them, there was nothing else in the size (175-14) in the way of a performance tire.

"up to a point, the harder you press, the better you hold" is completely false. Lower tire pressures generally (with older toyo's being notable exceptions!) tend to give BETTER grip, however, you increase risk of rolling the tire off the rim...

Lower pressure will give a larger contact patch, but I'd think at some point there has to be a crossover between area and grip.