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Old 03-15-2015, 07:38 AM   #1
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Self-Inflating Tires?

Very strange situation yesterday, thoughts welcome...

So, yesterday I took my Claas C into my local Ford Dealer to have my new DuallyValves installed on my rear tires. Finding a garage to actually do that work was really hard, but that's a whole different thread.

Anyway, MH is brand new for us and after the installation we took it out on a maiden road trip to put some miles on it and have the DW get some road time behind the wheel. When I picked it up from Ford we went home and loaded the doggies for a day on the road. While there I double-checked the pressure in all the tires and put on my TPMS a modules on all the tires. Pressure was dead on 80psi in each tire.

Took off and about 30 miles down the highway my TPMS alert went off showing over-pressure on the right rear outer tire. I pulled over to check the tire and sure enough the pressure reading on the TPMS monitor was right...88psi.

While pulled over, I checked all the tires again and all 4 rear axle tires were at 88psi. What the ? Tires temps were all showing about 70 degrees, so no overheating here.

How did all the tires increase nearly exactly 8 lbs in 30 miles? I've never heard of something like this in 30+yrs of driving. Has anyone ever seen this amount of change? I dropped the pressure back down to 80psi and we put another 300 miles on it with no problems or change in the pressures.

What would cause this? Any help?

Darren, Donna & The Wieners
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Old 03-15-2015, 08:08 AM   #2
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Do not know about at those pressures but 32 lb in a car tire car increase up to 4 lbs as the tires warm up.


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Old 03-15-2015, 08:20 AM   #3
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Yes, I've seen that amount, even in my pickup. But 8lbs in a standard 16" tire just seems very wrong!
Darren, Donna & The Wieners
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Old 03-15-2015, 08:42 AM   #4
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What you see is completely normal...not unusual for the pressures to increase 10 psi on a 80 psi tire. That's why TST instructions say to set the max pressure at 20% above the normal pressure ie 96 psi in your example.


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Old 03-15-2015, 09:01 AM   #5
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Pressure inside a tire increases 1 pound per each 10 degree increase in temperature. And they will lose 1 pound for every 10 degree drop in temp. Possibly, the temp inside the tires could have increased by 80 degrees. (Sunlight on one tire can increase internal tire temps by about 20 degrees more than a tire on the same vehicle in the sunlight. That I first noted in TN, when my first vehicle had internal TP sensors.)

Friction from incorrectly adjusted brakes, bad wheel bearings, etc., can also increase air temps inside a tire. But all at the same time? Probably not likely.

Another way to "magically" increase tire pressure is to increase in altitude. Since the pressure inside a tire is a direct relationship with external pressure, as you increase in altitude the external pressure decreases, thus the internal pressure increases. (However, usually as you increase in altitude the temperatures drop, so there might not be a very big difference. And a 5K increase in altitude will only be approximately 2 psi; thus would your gauge even register the difference?)

But it appears you live in IN, so it can't be altitude related
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Old 03-15-2015, 09:15 AM   #6
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Thanks guys! I mistakenly set my TPMS to alert at a 10% increase in pressure! Big oops there! I'll reset and drive on!

Darren, Donna & The Wieners
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Old 03-15-2015, 09:49 AM   #7
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Watch a little Nascar....The tires on them look almost flat until they make a few laps and generate a little heat in them thus increasing the pressure to where they really want them. The cars don't handle quite right until the tire pressure is built up. I think this is why tires are stamped with a cold air pressure rating, the manufactures know the pressure will increase to some other wanted value...

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