Tire pressure

[Glenn Basore]

Ok  all, this might sound dumb, but !

If the tire pressure is 60 psi cold and the tire is mounted on a rime the first time in the shop and inflated to the 60 psi, does that air pressure remain the same once it is mounted on the trailer or car and the load is now placed on it ?

I know race cars adjust the tires to the heat condition, if I tow a long distance should I let some air out to com-pansate for the heat that will build up ?

[brackish]

I think that the volume created by the tire remains the same, therefore the pressure remains the same.  The tire may change shape when weight is applied, but it keeps the same volume, therefore the same air pressure. .

The cold fill rating, I believe, already compensates for the possibility that the temperature of the tire will rise to the limits of  its heat rating.

I think that's true, however, very close friend is a tire engineer at the Cooper plant down the road, I'll ask him next time I see him.

[Red Planet]

Tire manufacturers caution you to fill the tire to the recommended inflation pressure when it's cold, and to never reduce pressure after the tire heats up. Here's a very informative link: www.carlisletire.com/product_care/trailer_tire_service_guide.pdf

The second page tells you pretty much what you need to know about maintaining proper inflation in trailer tires, whatever brand you chose to run.

[CaptRon28]

The recommended pressure is based on a cold tire and takes into account that the pressure WILL go up when the tire heats up at speed. Inflating it to anything less also WILL decrease the load rating of the tire and the trailer, possibly to the point where the entire rig is no longer safe at speed. If the load rating of all of the tires combined is significantly greater than the actual weight of the load, you can possiblly get away with it. Otherwise follow the recommendations.

This is based on actual load rating of the tires, and also because the properly inflated tires will flex less at speed and not generate as much heat in the process. Excessive heat is what causes most of the tire fragments on the side of the road. I imagine it would not be much fun adding to this debris.

Ron M.
Telstar 28, Horizon cat coming