[email protected] (Bill Pemberton) wrote in message news:<
[email protected]>...
> In article <
[email protected]>, joel roth
> <
[email protected]> wrote:
> >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.