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Old 10-08-2010, 07:04 PM   #1
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Tire Pressure

Took the motorhome out for just a ride today, temperature was 78 degrees. I have the pressure set at 80 front and 90 rear, that includes the 5 pound fudge factor. After about a half hour, my TPMS showed that my tire pressures had increased almost 5 pounds in each tire. The temperature reading of the tires was 95 degrees in all but one tire it was 97 degrees. At the end of the ride approximately one hour my front tires were at 90 and 91 pounds with temperature of 107 degrees. The rear tires were at 114 to 117 pounds and temperature of 110 to 114 degrees.

Can anybody enlighten be as to why the air pressure seems to rise so quickly and the temperature rose slower?

Maybe I am looking at something that is not a problem, but I am just curious.

Your input is appreciated

Thanks
Ed
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Old 10-08-2010, 08:33 PM   #2
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You should never take the tire pressure when the tire is HOT !
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Old 10-09-2010, 06:26 AM   #3
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Quote:
Originally Posted by smokey5209 View Post
Took the motorhome out for just a ride today, temperature was 78 degrees. I have the pressure set at 80 front and 90 rear, that includes the 5 pound fudge factor. After about a half hour, my TPMS showed that my tire pressures had increased almost 5 pounds in each tire. The temperature reading of the tires was 95 degrees in all but one tire it was 97 degrees. At the end of the ride approximately one hour my front tires were at 90 and 91 pounds with temperature of 107 degrees. The rear tires were at 114 to 117 pounds and temperature of 110 to 114 degrees.

Can anybody enlighten be as to why the air pressure seems to rise so quickly and the temperature rose slower?

Maybe I am looking at something that is not a problem, but I am just curious.

Your input is appreciated

Thanks
Ed
Go to the search bar at the top of the page and type in " tire information links" Should answer all your questions.
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Old 10-09-2010, 10:56 AM   #4
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Originally Posted by normandlegra View Post
You should never take the tire pressure when the tire is HOT !
Hi Norman... I don't think he was making any adjustments to his tire pressures based on "hot" pressure readings... he's merely reading the output of his TPMS while he's driving and there's no problem with that.

Rick
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Old 10-09-2010, 11:00 AM   #5
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Originally Posted by smokey5209 View Post
Can anybody enlighten be as to why the air pressure seems to rise so quickly and the temperature rose slower?

Maybe I am looking at something that is not a problem, but I am just curious.

Your input is appreciated

Thanks
Ed
I think I understand your question Ed and it's a good one. My gut tells me that it's not a problem but the dynamics of temp vs pressure rises do seem curious. I suspect it's a situation where the relationship between the two is not linear but I'm sure one of our experts will weigh in on it soon to enlighten us.

Rick
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Old 10-09-2010, 04:24 PM   #6
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Tire pressures increase about 2% for every 10 degrees of temperature change. That's 2 percent, not 2 psi. With a 30 degree temperature rise (fairly normal), that is an 3 x 1.6 = 4.8 psi increase in front and 3 x 1.7 = 5.4 psi in the rear. That would suggest 85 psi front and 95 psi rear, vs the observed 90 and 114+.

The problem is that the temperature is not uniform in the tire and the TPMS is reading local temps, probably by the valve. It appears the tire overall was hotter, leading to higher pressures. Unlike temperature, pressure changes are uniform throughout the tire.
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