Charles Fox

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
37 psi max (last reading).

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
cafox513@gte.net

Pete

"Charles Fox" <cafox513@gte.net> wrote in message news:XHVMb.2655$4P6.1801@nwrddc01.gnilink.net...
> 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
> 37 psi max (last reading).
>
> Seems a far greater leap than my "cooking" version radials, probably 65-70
> aspect ratio, on a sedan.

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

Mike Smith

Charles Fox wrote:

> 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
> 37 psi max (last reading).

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

> 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.

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

Charles Fox

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" <escape2music@hotmail.com> wrote in message
news:bu1ctd$gio$1@news.onet.pl...

"Charles Fox" <cafox513@gte.net> wrote in message
news:XHVMb.2655$4P6.1801@nwrddc01.gnilink.net...
> 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
> 37 psi max (last reading).
>
> Seems a far greater leap than my "cooking" version radials, probably 65-70
> aspect ratio, on a sedan.

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

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" <mike_UNDERSCORE_smith@acm.DOT.org> wrote in message
news:1008dvdn3nrd576@news.supernews.com...
> Charles Fox wrote:
>
> > 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
> > 37 psi max (last reading).
>
> That's more like 10%, not 0.5%.
>
> > 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.
>
> 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
>

John

Might just be moisture in the air.

"Charles Fox" <cafox513@gte.net> wrote in message
newsnZMb.9793$et1.8903@nwrddc03.gnilink.net...
> 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" <mike_UNDERSCORE_smith@acm.DOT.org> wrote in message
> news:1008dvdn3nrd576@news.supernews.com...
> > Charles Fox wrote:
> >
> > > 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
> > > 37 psi max (last reading).
> >
> > That's more like 10%, not 0.5%.
> >
> > > 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.
> >
> > 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
> >
>
>

elroy@seedy-impaler.com

On Tue, 13 Jan 2004 17:14:31 GMT, "Charles Fox" <cafox513@gte.net>
wrote:

>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
>37 psi max (last reading).
>
>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.


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

Charles Fox

Thanks, E!

<elroy@seedy-impaler.com> wrote in message
news:36re00d5hq16bunb3jmg781m46474ijbr6@4ax.com...
> On Tue, 13 Jan 2004 17:14:31 GMT, "Charles Fox" <cafox513@gte.net>
> wrote:
>
> >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
> >37 psi max (last reading).
> >
> >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.
>
>
> 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