Tire PSI question

[ace4059]

Man, That question got everyone fired up and lots of responses.
Heres another question. If I have 32 psi at sealevel and I drive to the mountians and am at 17,000 feet, did I loose any pressure since the air is thinner in the mountians. Or if I am in the mountians at 17,000 feet with 32 psi in my tires and I drive to sea level did I gain presure in my tires due to the fact that the air is greater or more dense and is pushing more on my tires.

IMHO I think that atmospheric presure and weight do make a difference in tire pressure. But it may only may make it increase or decrease by .001 psi. Whith is not enough to tell or read with a tire presure guage. This is kinda like the water in a swimming pool. Say you mark the level of the water on the side of the pool. Then you jump in. Did the water level rise. Yes it did because your body displaced some of the water. Now you look at the mark on the pool. But the water is at the same level on the mark. This is because even though your body displaced the water and caused it to rise, the rise of the water is not enough to be noticed.

[Terry Lingle]

since for all practical purposes the amount of air and the enclosing volume do not change the internal pressure will not change. The gauge pressure will however reflect the change in external pressure which you might mistake for a change in internal pressure.
The tire will be incorrectly inflated after the 17,000 ft change in altitude because the desired inflation pressure is referenced to the ambient pressure. I will ignore temperature changes for this discussion.
Terry

[JD in SoCal]

since for all practical purposes the amount of air and the enclosing volume do not change the internal pressure will not change. The gauge pressure will however reflect the change in external pressure which you might mistake for a change in internal pressure.
The tire will be incorrectly inflated after the 17,000 ft change in altitude because the desired inflation pressure is referenced to the ambient pressure. I will ignore temperature changes for this discussion.
Terry

In other words, the gauge will read the difference between the pressure inside the tire and the ambient pressure (outside the tire). If your tire pressure is set correctly at sea level and you drive to higher elevation, the tire pressure will read higher, which accurately indicates that the pressure differential (inside to outside the tire) is greater. The tire pressure should ideally be adjusted to the correct pressure at any given elevation.

Regarding tire temperatures and pressure, the temperature will also significantly affect the tire pressure. As long as we are debating this, one should be aware that temp is a factor that will swing the pressure by at least several psi. When precise tire pressure is really important (race cars), tire temp is a factor that is closely monitored. In street use, it may not matter a lot most of the time. However, if you are driving on a trip for example, the temp could swing 50 degrees or more in a day. Don't think that the pressure that was correct in the morning in a cold hotel parking lot will still be correct when you drive through the desert that afternoon.

JD

[Terry Lingle]

For most tires the manufacturer specifies the inflation pressure cold. The tire design has alarge enough optimum inflation pressure zone that changes in tire temperature and elevation do not pose significant problems.

Raceing tires are a completely different subject . Altitude changes are usually pretty minimal but temperature changes can be critical. Terry

[JD in SoCal]

The tire design has alarge enough optimum inflation pressure zone that changes in tire temperature and elevation do not pose significant problems.

Come on now, Terry. You're letting reality get in the way of a good conversation. Most humans ignore their tire pressure and couldn't care less what affects that pressure or how it is affected. A higher level of curiousity about how things work is the reason for most of the conversations on this board.

That being said, you are 100% correct, of course.

Raceing tires are a completely different subject . Altitude changes are usually pretty minimal but temperature changes can be critical. Terry

I ran an SCCA road race car for a while in my past, and a big part of the fun is figuring out all the tiny factors that add up to making you go fast (or not). Many factors that we can all ignore on road cars and other machines are important to understand and address in racing. It makes a guy use his brain effectively if he wants to be successful, and also can generate some knowledge that hopefully a guy can apply to other subjects in life.

JD

[whateg0]

Raceing tires are a completely different subject . Altitude changes are usually pretty minimal but temperature changes can be critical. Terry

Which is why those better funded teams (not ours) use nitrogen, which is much less susceptible to changes in temperature. The rest of us rely solely on bleeder valves, which stick and let all the air out of your tire and then you... Sorry, I digress. BTW, I believe it is the moisture in the air which causes the volume to change so drastically.

Dave

[MJL]

As a guy who works in a tire factory, this has been an entertaining thread.

[walker]

And also a very old thread, as they stopped using stone tires some time ago.

[MJL]

Tire guages measure "gauge pressure" so it will show an increase at higher elevations, if it's enough to cause a significant drop in atmospheric pressure.

Coffee as a liquid will undergo no appreciable volume change from pressure. You were experiencing something else.

He probably shook the bottle as he opened it.

[cboerema]

first things first. what color is the car? just havin fun, but on a finer note.The company i was working for had the owners kid as shop boy. Now one day the boss calls me and says would you stop in the shop and help the kid put one of the steer tires from the crane in the pickup so the kid could take it to get repaired, sure no prob. when i get to shop i find the kid letting the air out of the slow leaker.i ask him why is he lettin the air out cause theyll just have to put it back in to find the leak. {high school graduate] his response was it had 85 pounds of air in it and wanted to lighten it up. ??????????? I was astounded as i never gradiated school!