Tire Pressure?

[Wishno87]

Thanks for the explanations guys. Had to drive the vert for a few weeks this winter and 17in wheels + winter roads = some interesting pothole avoiding maneuvers.

[e30_325es]

Air is compressable and therefore can't bend your rim by hitting a pothole. What bends the rim is the blunt force of the pothole exerting a force that cannot be absorbed by the tire itself (ever notice it's easier to bend a rim that has less tire on it/a lower profile tire on it?).

The reason why you should run the same pressure regardless of the diameter of the tire or rim is because there is the same pressure in each tire. The volume of the air might be less, but the pressure exerted by the air is the same.

[E30SPDFRK]

The wheels bends by the tire (with the road behind it) coming up and hitting the wheel. Tire pressures won't make too much of a difference here unless we're talking about wicked low pressures (<20). Tire pressures are used to keep tread wear even and to keep the tire seated properly, and most tire manufacturers spec between 32-35 to be optimal.

[Wishno87]

Could you give me a more detailed explanation? Because on a low profile tire there is less impact that can be absorbed by the tire before it hits the wheel no? Unless the air being pressed against the wheel is what causes it to get bent.

[e30_325es]

no.

[Wishno87]

Gais?

[Wishno87]

I know im bumping an old thread guys but does tire pressure also depend on aspect ratio? For example should i run higher pressure on my 17 than i do on my 16 or 14 to protect the wheel?

[Hallen]

^^Pyrometers are nice for that too.

Yes, they are. If you don't have one, you have to look for tread wear and what I call rubber liquefying. It's that strange look the rubber gets after it has been fully heated up on the track. You also look for where the heating stops on the outside. In other words, how far over was the tread rolling in the corners. How far on the sidewall is the wear. There is generally a mark on most tires that you don't want to go beyond. If you are on the line or over, you need to bump up pressures even if the tires are already getting too hot.

[rThor432]

^^Pyrometers are nice for that too.

[Hallen]

It does depend a lot on the type and brand of tire you are running and how hard you are driving the car. Higher pressures are nice in that you can get better gas mileage and it can help to stiffen up the sidewalls, especially for higher profile tires. Low profile tires need pressures that are a tad higher to insure that you don't bend a wheel on a bump.

Hot pressure is the key. But unless you are tracking your car, you shouldn't need to worry about it. Set what feels good (within the specs) and then watch your tire wear. If the center wears out faster than the edges, then your pressures are too high. If the outside edges wear out faster than the centers, you pressure is too low. (camber must be taken into consideration here.)

[Erick]

BMW says that the optimal is 32psi all around, or 36 (might be 38 ) psi in the rear in case there are passengers + trunk full.

Just don't ask E-Rich what he runs. :p I thought I was crazy for rocking 45psi.

[dude8383]

I usually run about 36 on street tires

werd, i just mounted my summers and inflated them to 36 psi all around. have been pumping them up @ 36psi for the past 3 summers and the wear is very even.

[asubimmer]

I usually run about 36 on street tires

[Jordan325iC]

I run my tires at 38-40psi normally. I don't mind the ride harshness, and I understand that higher pressures = better gas mileage. Is there a downside to doing this?

[rThor432]

Not at all actually. My 195/65/14's on the 318is wore perfectly even, even with the H&R Race springs (which I later changed out for the Sports).

My S52 car isnt a daily driver, but I only inflate those tires to 33-35 tops. Those tires wear evenly as well.