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Topic: Another Tire Pressure Tidbit (Read 3 times) previous topic - next topic
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Another Tire Pressure Tidbit
Yahoo Message Number: 48812
Two weeks ago I topped my tire pressures off in FL, at 70F, and the tires maintained pressure just fine the rest of the trip.

This morning as I was shovelling snow in the driveway, I heard a faint electronic beeping, which was my low level (down 12.5%) tire pressure monitor alarm.  I checked all tire pressures, and, yup, they were all down about 8 psi, due to the 40F temperature difference.

I had forgotten how much pressure you can lose/gain with the difference in temps between warm & cold areas.
Re: Another Tire Pressure Tidbit
Reply #1 –
Yahoo Message Number: 48833
-- A good ball park figure to use is 1 degree tire pressure drop/increase for each 10 degrees of temp. change.
Other likely suspects that frequently account for pressure differences: Slow, and perfectly normal, leaks through the tire wall, valve stems, rims, etc. and less than perfect accuracy of gauges.

Ed

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Two weeks ago I topped my tire pressures off in FL, at 70F, and the tires maintained pressure just fine the rest of the trip.

This morning as I was shovelling snow in the driveway, I heard a faint electronic beeping, which was my low level (down 12.5%) tire pressure monitor alarm.  I checked all tire pressures, and, yup, they
Re: Another Tire Pressure Tidbit
Reply #2 –
Yahoo Message Number: 48851
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A good ball park figure to use is 1 degree tire pressure [1 psi?] drop/increase for each 10 degrees of temp. change. ed

Two weeks ago I topped my tire pressures off in FL, at 70F, and ... were all down about 8 psi, due to the 40F temperature difference. biker06365
An interesting problem.  I went and found my college physics book and did the calculation.  1psi for a 10 degF change is about right for a low pressure car tire.  At higher pressures its bigger and oddly, the change is larger at low temperatures.

The calculation says that the change varies from 1.4psi/10degF for 60psi and 90degF to 1.9psi/10degF for 80psi at 30degF.
If biker06365's tires were inflated to 75psi, I calculate a 7psi change from 70degF to 30degF so the calculation method more or less works.  If you remember that it's a bit less than 2psi change for every 10 degreesF it will tell you when to check your tires.

Altitude change will make the indicated or gauge pressure vary a bit also.  Since a gauge measures the difference in pressure, between the atmosphere and the tire, when you go up in altitude 1000', all things being equal (a big if, here) the tire gauge will indicate that the tire has GAINED about 1/2psi of pressure.  I have looked for that change but never could see it.

I also noted the other day that the pressure dropped about 1/2 psi when I jacked up a front wheel. Load apparently also changes the tire's pressure a tiny amount.

Linley
Re: Another Tire Pressure Tidbit
Reply #3 –
Yahoo Message Number: 48867
--- In lifewithalazydazerv@yahoogroups.com, "lfgcfg"  > >

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biker06365
Very interesting. Thank you.
When I bought my new tires a few weeks back, I had the shop fill the tires to 80#. I then monitored the air pressure every day for a week to satisfy myself there were no air leaks as a result of the installation process, valve stems, extenders, etc. I took the pressure readings each morning at 7am on my way out the door to work. I wish I had recorded the temperature but didn't. I found significant differences from day to day but finally concluded the tires had no leaks.
I've since adjusted tire pressure based on actual weight being carried.
Ed