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Old 06-24-2008, 09:48 PM   #1
Senior Member
Join Date: Aug 2007
Location: New York
Posts: 404
SUN #385
tire pressure increase

I checked the Sunline tire pressures after the Winter and I brought them up to 50lbs sometime in the Spring. I just checked the pressures today and they range from 54 to 55 lbs. The Sunline tires are never in the sun.

The ambient temperatures are now somewhat higher than they were in the Spring so I can understand why the tire pressures went up. My question is should I leave the pressures alone or should I drop them back to 50 lbs? I only ask because even with 55 lbs of pressure they don't look hard, they still show some sag at the pavement.


2007 Ford F150 FX4 Supercab 4x4, 5.4 FFV engine, 3.73LS.
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Old 06-24-2008, 10:10 PM   #2
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Join Date: Aug 2007
Posts: 280
SUN #382
You should set your tire pressures for the current ambient temperatures.

For those that don't know the effect of air temp and time on tires....

You should expect that:

For every 10 degree drop in temperature, the pressure will be 1 pound less than at whatever you set them at when you did it last....

also, you should expect to lose around one pound of air per month.

SO, if you set the pressure at 50 psi while the air temp is 80 degrees F in July (the beginning), and then you add no air, and check the pressure when the temperature is 40F and in November (say mid-), the best pressure you should find would be 41 psi, if the tires are in average condition and filled with air instead of nitrogen.

50 psi - (1 lb x 5 months) - (1 lb x 4 (sections of 10 degrees)) =

50 - 5 - 4 = 41

I don't know the figures for Nitrogen, as it was not a popular option when I was taught by Michelin....back in the mid 90s (nice trip paid for by my employer at the time and Michelin).

Kelly & Greg Southeast MA
'04 2500HD Silverado
'05 2380s Solaris Lite, axles flipped
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Old 06-25-2008, 05:51 AM   #3
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Join Date: Aug 2007
Location: New York
Posts: 404
SUN #385
Thanks Greg, that is great information.

I didn't realize that outside temperature had that much effect on tire pressure but it does makes sense that it would.

I'll air them down to 50 lbs!

2007 Ford F150 FX4 Supercab 4x4, 5.4 FFV engine, 3.73LS.
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