Lower temp means less Brownian Motion. Air molecules settle to the bottom and quietly slip out. *NM*

Or at least it seems that way. I haven't driven my Boxster more than once in the past two months, and today I notice the tires are about 5-6 pounds down per tire. When I drove the car everyday, they hardly ever lost air. Ditto with my SUVs tires. I have a tire pressure monitoring system in that car, and since I'm using it as a daily driver during the winter, I haven't lost any tire pressure in these two months. What's causing the air to escape when the tire sits still vs when the tire has heat cycles?

As a precaution now, I over inflated the tires about 5 pounds in the Porsche because I know it's gonna sit still for another 2 months.

My bike tires get pumped up in the spring and seldomly need air during the season. After storing it in November, the tires will be flat by the time I get it out in April.

Never really checked it in the Boxster since I pump up the tires to 55 lb when I store it. Second thing I do in the Spring is let air out of the tires to bring them back down to operating pressure.

I'll try to remember to check the pressure this Spring before I start letting air out of the tires. .......wish that was tomorrow.

[www.kenkifer.com]

it's pretty entertaining

Loved the list.

Any idea where I can get one of those vibrators? That sounded like the most logical one to me.

versus the lack of driving?

You lose "x" psi for ever "y" degree of temperature drop - don't remember what x and y are, but I'm sure one of our smarter posters knows!

Ed

Treating the stuff inside the tire as an ideal gas at constant volume (decent approximations) means that pressure is proportional to the product of temperature and the number of air particles (mostly molecular nitrogen, I think). If either the temperature or the number of particles is reduced, then pressure goes down. If you suppose that the volume isn't fixed, then the pressure is still proportional to the product of temperature and the number of particles in the air, but now also inversely proportional to the volume.

It seems to me that somehow air leaks out of tires faster when the tires aren't used. One way to check this would be to measure both the tire pressure and temperature just before parking the car for the winter. Then months later, raise the tire's temperature back to whatever it was when you first parked it and then measure the tire pressure. If the pressure is not the same as when you first parked the car, and if the volume of tire is the same as when you first parked it, then some of the tire's air has leaked out. The hard part would be to find out if more air leaked out then if you had driven the car. So really you would have to repeat the experiment keeping everything the same except that you now keep the car in use during the winter.

It seems to me that you would find out that a parked tire does lose air faster than a tire that is driven on occasion. That's just my feeling from personal experience though. I don't know if it is actually true. And if it is true, I don't know why.



Edited 3 time(s). Last edit at 01/03/2011 08:17AM by Steve (Berlin & LA). (view changes)

Yep, when I drove the car thru the winter in years past, it did maintain pressure. Must be the heat cycling from regular use that keeps it from leaking.

Living in California, I don't have experience with extended storage; however, I find that the pressure decreases much less when my tires are filled with 100% nitrogen.

I don't see how an extra 20.9 percent nitrogen can make a significant difference.

I read that nitrogen is better in tires because the molecules are larger then those that make up the components in tires. I'd imagine as the tire heats, it expands, allowing more space for the air to seep through with increased pressure to force the issue (think Playdo and one of those Playdo machines to make things). With the larger nitrogen molecules you get less seepage. I'm not a chemist, nor do I play one on TV, so not sure if that is accurate, but sounded reasonable.

When i store tires, they typically lose around 3-7 psi "depending" over a 8-9 month period. That's pretty good.

OTOH when i have them on the car i am constantly adjusting for temperature, do i cannot say for sure.

All i know is that during storage, i never get a nail, which tends to accelerate air loss.

Grant

Edited 2 time(s). Last edit at 01/03/2011 04:26PM by Laz. (view changes)

is it p = pressure and V= volume and k is the constant value or is it porsche (boxster since it is a small p) x Velocity (which is fast as it is a big V) = k or constant changes in the pressure in your p tires when we drive them fast?

Edited 1 time(s). Last edit at 01/05/2011 12:59PM by Capt Ron. (view changes)

Something doesn't have to cogitate to have consciousness. I'm grasping at straws here and I'd have to re-peruse The Web of Life to be sure. As for Dark Rubber, I'd rather leave that to Nietzsche.