Correct Tire Pressure

I was just thinking (or not) are tire pressure settings based on the car or the tire.....

I'm not sure. Please oh GRM wizards learn me up!

The car, the tire, the driver's preferences...

Generally, I would say the car and what is in the owners manual. That being said, most folks here are probably running tires that are not OEM size which will likely make it way different.

Two posts in and nobody has suggested a pyrometer?

I'm not a fan of following the manufacturer's pressure. Odviosuly, they don't just pull them out of um... a random number generator, but I find that the manufacture's priorities don't align with mine. Like mazdeuce said, I like to use a pyrometer.

OEM tire pressures are based on the car manufacturer's attempt to balance fuel economy, comfort and, to some degree, performance.

For me, ride comfort is not a priority so I run higher pressures than recommended in the car's manual or even what's on the side of the tire. I'll take stiffer sidewalls and lower rolling resistance for better cornering and mileage.

Are the tires made by Sandoz Laboratories?

Maybe I should give a bit more info. My 16yr old daughter has a 91 MR2. I bought her a set of rims from Tire Rack and they came with different settings so now I am trying to figure out what is right for her setup.

Thanks!

34 psi

So many factors to say: weight of car, stiffness of sidewall, location, driver style, ambient temperature, tire size. I generally start in the low 30's for most cars. Large diameter tires like more air; small cars ie miata need less air. Pyrometer really doesnt help much on the street but checking temps should give you an idea of the stress on the tire and which direction you need to go.

I usually go by the car's rating posted on the door frame. Going much higher or lower can affect tire wear, handling and ride. Of course in a competitive condition, all of that is thrown out. Tires rarely get hot enough in daily driving for a pyrometer to be helpful . I was told once, that if you don't know, 32-35 is a good start.

The old trick of white shoe polish at the tread/sidewall area might work...

shadetree30 wrote: The old trick of white shoe polish at the tread/sidewall area might work...

I don't know this trick yet I am old... Can you explain please.

I start with what the door jamb says and adjust from there.

Tire temps tell the tail. Go down a 1 mile streatch of hiway that is straight pull over gentaly and check temps. shoul be about 5 deg difreance across tread at the most.

Is she a performance driver, or vehicularly challenged?

If its the first, pyrometer, or personal preferences. She'll know more than you anyway.

If it's the second, teach her how to read the door jamb, so she'll always know the proper info is written right on her car.

Ok going back to my original question by checking the door jam are you saying the car determines the pressure no matter what rims/tires are on it?

I take the pressures listed on the door jam as minimum allowable, or suggested starting point. I find most passenger cars ride & respond best when inflated 4 to 8 psi above the recommendation on the door tag.

As to the OPs question, whats on the door tag is for the same size and speed rated tire as factory equipment. Going up one, or even two inches in rim diameter would probably not make a huge difference if the tires being used are similar to the OE type tires.

The only proper way to do it is by chalking the tires or using a pyrometer. Here's what I do:

http://www.ehow.com/how_6948382_chalk-tires.html

To the OP: correct tire pressure is determined through the chalk method but is influenced by literally every aspect of the car. If the tires are the stock size and brand, then use the pressures on the door jamb. Any other tires, and it will pay of in the form of safety and longevity to use the chalk method.

Pressure goes by weight. The heavier the car, generally the higher thepressure. Cept for the pesky germans. Changing the size of the tyre should not effect inflation all he much. Mr2 is 30 stock? If u went with a 35 series tyre I would maybe bump up the pressue 5psi cold. Never exceed the max inflation on the sidewall. Pyrometer is the easiest way to tell what the correct pressure should be tho. You can tell by wear, but then its usually too late.

Oh, and to be always be at /the perfect/ pressure, you should do the chalk test every single time the amount of weight in the car changes at all, and every tire should have it's own individual pressure. For example if you use a gallon of gas, then that's 6 pounds less that the car weighs. So you should pull over and lower tire pressures a fraction of a decimal point to account for the change. You should also adjust pressures before each corner according to its radius, traction, entry speed, etc. This isn't practical of course, but the idea might help you understand the variables we're working with here.

Sultan wrote:

shadetree30 wrote: The old trick of white shoe polish at the tread/sidewall area might work...

I don't know this trick yet I am old... Can you explain please.

It's also called the "chalk test", but apply a contrasting medium (chalk or white shoe polish) to the junction of tread and sidewall (continuing up the sidewall approx 1-2"), drive the car and see where the white stuff is worn off.

That's really only for track work. For the street you chalk across the face of the tread and look for even wear.

I love this place and Tom you are awesomeness!

Thank you all!!