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post #1 of 18 (permalink) Old 12-14-2007, 11:05 PM Thread Starter
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Tire pressure & temperature drop

A newbie question - factory tire pressures (28psi front, 30 or 32psi rear) drop some as the temperature drops. As you drive, doesn't that warm the tires up to the factory specs, or is it necessary to further inflate them back up to factory specs. Thank you in advance.

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post #2 of 18 (permalink) Old 12-15-2007, 12:05 AM
 
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Quote:
Originally Posted by jonathanrsr View Post
A newbie question - factory tire pressures (28psi front, 30 or 32psi rear) drop some as the temperature drops. As you drive, doesn't that warm the tires up to the factory specs, or is it necessary to further inflate them back up to factory specs. Thank you in advance.
yes, inflate your tires before you ride. otherwise you will possibly have tire failure due to excess heat caused by friction of your tire. they will build heat, pressure, but that is NOT good.
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post #3 of 18 (permalink) Old 12-15-2007, 11:45 AM
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I think the question is - if I filled the tires when it was 80 degrees out and want to ride when it's 40, do I have to adjust for the temperature difference?

Right?

While you should check your tire pressure before every ride, the pressure difference is negligable with the range of temperatures a sane person would ride in.
Quick chemistry lesson...

PV=NRT (T is in kelvins) - P is pressure, V is volume, N is number of molecules (in moles) and T is temperature in Kelvins. Simple algebra will change the formula to P=T/V

30 degrees farenheit = 272 kelvin
100 degrees farenheit = 310 kelvin

I don't feel like working the math, but at 32 psi that gives a pressure drop of about 4 psi (many gauges are only accurate to 2 or 3) and most people don't ride in that wide a temperature range.

All that to say - it's a good idea to check your tire pressure before each ride, but the change in pressure due to temperature is generally negligible. (and yes, the tires will heat up some during a ride making same difference even more negligible).

Ok... gotta run to work...

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post #4 of 18 (permalink) Old 12-17-2007, 11:16 PM
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I was always taught that you fill your tires when they are cold. Been doing that for 40 years.
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post #5 of 18 (permalink) Old 12-18-2007, 02:21 AM
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You DO fill your tires when they are cold... but I think the original question was about temperature (weather) change and it's effect on tire pressure...

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post #6 of 18 (permalink) Old 12-18-2007, 09:08 PM
 
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Its been cold here. And my front tire was definately mushy!
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post #7 of 18 (permalink) Old 12-18-2007, 09:54 PM
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Also everything shrinks with the cold, you might get leaks through the valve stem, so tighten it. Also one might get a little leak around the sealing bead of the tire. Like mentioned above check tire pressure often.

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post #8 of 18 (permalink) Old 12-18-2007, 10:33 PM Thread Starter
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Thank you...

gentlemen, for your replies. Curtis, thank you for your in-depth explanation. I check the pressure before every ride, and only recently have we had cold (30's) temps, and that's when I noticed the pressure drop.

niterider, good observation! I didn't pay much attention to the top of my valve stem cap until I noticed a 2 lb drop overnight. Turned out that as I was trying to get my tire guage on the valve stem, I loosened the threaded part of the valve stem, and the air leaked out. THAT's when I realized why the top of the valve cover was notched. DOH *G*

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post #9 of 18 (permalink) Old 12-19-2007, 10:36 AM
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Quote:
Originally Posted by curtis97322 View Post
I think the question is - if I filled the tires when it was 80 degrees out and want to ride when it's 40, do I have to adjust for the temperature difference?

Right?

While you should check your tire pressure before every ride, the pressure difference is negligable with the range of temperatures a sane person would ride in.
Quick chemistry lesson...

PV=NRT (T is in kelvins) - P is pressure, V is volume, N is number of molecules (in moles) and T is temperature in Kelvins. Simple algebra will change the formula to P=T/V

30 degrees farenheit = 272 kelvin
100 degrees farenheit = 310 kelvin

I don't feel like working the math, but at 32 psi that gives a pressure drop of about 4 psi (many gauges are only accurate to 2 or 3) and most people don't ride in that wide a temperature range.

All that to say - it's a good idea to check your tire pressure before each ride, but the change in pressure due to temperature is generally negligible. (and yes, the tires will heat up some during a ride making same difference even more negligible).

Ok... gotta run to work...
Using 100F @ 35psi, 10L for vol, .93 moles, calucating for 30F, all other variables remain the same yields 30.6 psi, that is a significant change, worth correcting.

Jon

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post #10 of 18 (permalink) Old 12-19-2007, 02:56 PM
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Quote:
Originally Posted by jonathanrsr View Post
gentlemen, for your replies. Curtis, thank you for your in-depth explanation. I check the pressure before every ride, and only recently have we had cold (30's) temps, and that's when I noticed the pressure drop.

niterider, good observation! I didn't pay much attention to the top of my valve stem cap until I noticed a 2 lb drop overnight. Turned out that as I was trying to get my tire guage on the valve stem, I loosened the threaded part of the valve stem, and the air leaked out. THAT's when I realized why the top of the valve cover was notched. DOH *G*
Ok, so you are saying you psssst'd out 2 lbs of air

(Sorry, couldn't resist!)

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