Re: Tire pressures

Posted by DavidPackard On 2022/12/25 21:01:08

Ten psi per 100°F would appropriate if, the cold pressure was 35-36 psig, and the volume of the tire did not increase with pressure. Since MC tires tend to be ‘stiffer’ than its automobile counterpart an assumption of constant volume is likely better for MC tires, but not for automotive units where the tread was intended to be in contact with the road over the full width. We know if an automobile tire is over-inflated the tread wears in the middle and that deflection will likely increase the internal volume. This increase in volume will reduce the pressure rise due to temperature. And then there is the rubber compound of a motorcycle tire. They tend to be formulated for traction, not longevity, so there is likely unrecognized motion of the compound at the ‘patch’, hence a bit warmer than the automotive counterpart with a ‘harder’ compound designed for both traction and ‘mileage’. Rear motorcycle tires have a rather short service life. I never got much more than 10000 miles on a larger bike, even less, that is quite a bit less, if the bike had a good amount of power.

I think there are two conditions that apply as to the differences between motorcycle and automotive tires. First the motorcycle tire will likely not expand as much as an automotive tire as addition pressure is applied, and second the rubber compound differences will likely favor the motorcycle tire to achieve a higher operating temperature. Wat however didn’t mention that the quoted data applies for the time he did 25 hot laps on the Springfield mile.