Audi: Low-aspect ratio tires: pressure gain?

"Charles Fox" <net> wrote in message news:XHVMb.2655$gnilink.net... 

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

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

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>


"Pete" <com> wrote in message
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"Charles Fox" <net> wrote in message
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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

That makes just a whole lot of sense, Mike. Maybe I'll try it on the service
guys when I'm there. Thanks!

"Mike Smith" <DOT.org> wrote in message
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goes 
36 or 
65-70 

Might just be moisture in the air.

"Charles Fox" <net> wrote in message
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service 

On Tue, 13 Jan 2004 17:14:31 GMT, "Charles Fox" <net>
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