# Low-aspect ratio tires: pressure gain?

• posted on January 13, 2004, 5:14 pm
Am I right in my first blush . . . that my 33psi (cold) tire pressure goes way up when driving? I'm talking a jump of 0.5% or more, to as much as 36 or
Seems a far greater leap than my "cooking" version radials, probably 65-70 aspect ratio, on a sedan.
Thanks for any insights you may have.
--
Charles Fox
snipped-for-privacy@gte.net
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• posted on January 13, 2004, 6:20 pm

It is normal for tire pressure to increase by a few PSI when driving since the tires and the air in them heat up. That's why you're supposed to measure it when tires are cold. However, I don't remember it being only a low-aspect ratio tire phenomenon (by the way, what tire size are we talking about here?). All my tires did this.
Also, you will gain about 1 extra PSI for every 10F increase in ambient outside temperature.
Cheers,
Pete
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• posted on January 13, 2004, 9:25 pm
Thanks, Pete. My tires are the TT V6 one-grade-up tires, 225 40 aspect ratio 92Y. "Sorry, dear, they were already on the car." <g>

or
It is normal for tire pressure to increase by a few PSI when driving since the tires and the air in them heat up. That's why you're supposed to measure it when tires are cold. However, I don't remember it being only a low-aspect ratio tire phenomenon (by the way, what tire size are we talking about here?). All my tires did this.
Also, you will gain about 1 extra PSI for every 10F increase in ambient outside temperature.
Cheers,
Pete
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• posted on January 13, 2004, 6:24 pm
Charles Fox wrote:

That's more like 10%, not 0.5%.

Just a guess here - the lower-aspect tire contains a smaller volume of air, but the heat generated by friction is related to the surface area that contacts the road, which for tires of similar width should be similar. So in the lower-aspect tire, you have a smaller volume of air receiving a similar quantity of heat, thus a greater rise in temperature, thus a greater rise in pressure....?
-- Mike Smith
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• posted on January 13, 2004, 9:25 pm
That makes just a whole lot of sense, Mike. Maybe I'll try it on the service guys when I'm there. Thanks!

goes
36 or

65-70
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• posted on January 15, 2004, 2:02 am
Might just be moisture in the air.

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• posted on January 16, 2004, 4:38 am
wrote:

Absolutely. From autocrossing experience, I've measured on average 2-3 pound increases in sequential runs for the first couple of runs. I've had to remove up to 7-8 or eight PSI to keep the tires at 40 PSI when the pavement was hot. A four pound increase is not unusual once the tires get warm.
Elroy 2000 S4
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• posted on January 20, 2004, 5:46 pm
Thanks, E!

goes
or
65-70