Tire Pressure Variances and Base Setting- Maximum PSI When Cold vs Towing

Question:

I have Westlake G rated tires on a 2-axle 5th wheel, with a recommended pressure of 110 psi. I am monitoring pressure with a TST TPMS. Pressure when I start out in the morning has been 103 - 108 psi, wether it is 55 degrees or 75 degrees outside. Over a couple hours, the pressure ranges from 116 - 122. If the optimal psi is 110, what psi should I start out with? If I set it at 110, one or more tires will probably exceed the max psi setting of 125.

asked by: Shep

Expert Reply:

To briefly answer your question before I get into a more detailed explanation, you'll want to start the tires at 110psi.

The recommended/optimal tire pressure rating of 110psi for a tire like the Westlake ST235/85R16 # LHWL410 (which has a Load Range G) is going to be the recommended pressure for the maximum load when the tires are cold; this simply means after sitting overnight or for a few hours in the shade. It is expected as the tires are used, especially when towing, that you will experience a rise in air pressure within the tires. Tire companies take this into account when testing their tires and recommending the maximum psi rating. You should never exceed the cold pressure rating when inflating tires, since the amount it will raise when they get warmed up will exceed the safe maximum. It should also be noted that tires not inflated properly, or tires used over the maximum speed rating heat up quicker and are easier to damage.

Long story short, if you keep your tires inflated correctly when cold, they won't let you down when they heat up. Under-inflation is actually going to lead to more heat build up and a higher psi gain than if you just inflated them to the recommended psi.

Hopefully that all makes sense!

expert reply by: Erik B