Pressure loss in cold weather

In article <[email hidden]>, joel roth

Quoted message said:

How many PSI do my tires lose going from indoors (70 degrees) to outside (35 degrees)?

I recall from high school physics: Pressure * Volume/Temp, but what is is the volume of a road tire
or a mountain tire? and what's the equation for PSI into metric units? I can figure out the
temperature in metric units.

You don't care about volume in this case since it won't change (so your equation becomes
P1/T1 = P2/T2).

Temperature must be in an absolute unit, but either Kelvin (C + 273) or Rankine (F + 459) will work
fine. You can leave the pressure in
PSI for either temperature.

So a tire that is 120 PSI at 70 F will be 112 PSI at 35 F.

--
Bill

joel roth said:

How many PSI do my tires lose going from indoors (70 degrees) to outside (35 degrees)?

Not enough to worry about.

Just remember to use Kelvin as you are comparing absolute temps.

--
Bruni Bicycles "Where art meets science" brunibicycles.com
410.426.3420 joel roth <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

How many PSI do my tires lose going from indoors (70 degrees) to outside (35 degrees)?

I recall from high school physics: Pressure * Volume/Temp, but what is is the volume of a road
tire or a mountain tire? and what's the equation for PSI into metric units? I can figure out the
temperature in metric

units.

Quoted message said:

Thanks

joel

Joel Roth said:

How many PSI do my tires lose going from indoors (70 degrees) to outside (35 degrees)?

In the days of tubulars, that we had to pump daily due to their thin latex tubes, cold weather was a
blessing of sorts because they didn't leak down as fast. I'm not sure how large the effect was but I
recall when it was cold on trips in the Alps that we could get along fine with pumping every second
day. That was a while ago though.

Jobst Brandt [email hidden]

[email hidden] (Bill Pemberton) wrote in message news:<[email hidden]>...

Quoted message said:

In article <[email hidden]>, joel roth

Quoted message said:

How many PSI do my tires lose going from indoors (70 degrees) to outside (35 degrees)?

I recall from high school physics: Pressure * Volume/Temp, but what is is the volume of a road
tire or a mountain tire? and what's the equation for PSI into metric units? I can figure out the
temperature in metric units.

You don't care about volume in this case since it won't change (so your equation becomes P1/T1
= P2/T2).

Temperature must be in an absolute unit, but either Kelvin (C + 273) or Rankine (F + 459) will
work fine. You can leave the pressure in
PSI for either temperature.

'absolute' pressure not 'gauge'; add 15-psi. be sure to stand outside & wait about an hour or so to
let the tire temperatures stabilize. you have to hold the bike tires off the ground to keep the
ground contact, snow?, from influencing the results. oh yeah, you have to pump up the tires
rrrrreeeeeaaaallllll ssssslllllloooooowwwwww to keep the heat of compression from altering the
results. again, best done outside so you don't pump indoor air, hot & humid, into the tube. done
over a hour or so might be OK. of course, once you start riding, the cord flex will heat the tire to
possibly dangerously high pressures so don't overdo it. you might want to ride real slow and stop to
check the pressure a few times, every 5 minutes or so over the first couple of hours sounds pretty
good to determine any heating trend.