Community Forums

scbwr · 08-29-2020, 01:49 PM

The OP's tire pressure settings are consistent with the inflation chart for the Toyo tires on my Bay Star. I've been running 93 on the rears and 85 on the fronts and that is adding a few lbs. of pressure as a safety margin since I was only able to get front axle and rear axle weights. At some point, I'd like to get weights by individual wheels.

davidceder · 08-29-2020, 03:10 PM

Hey Rev Roy;

Not according to what kenharris911 posted in post#2 from tire rack. See below.

"Since a tire mounted on a wheel essentially establishes a flexible airtight (at least in the short term) pressure chamber in which the tire is shaped and reinforced by internal cords, it retains the same volume of air molecules regardless of its elevation above sea level. However, if tire inflation were set with a tire pressure gauge at sea level (where the atmospheric pressure of 14.7 pounds per square inch is used as ambient atmospheric pressure by the gauge), the same tire pressure gauge would indicate the pressure has increased at higher elevations where the ambient atmospheric pressure is lower. Those measured at the 5,000-foot level (where an atmospheric pressure of only 12.2 pounds per square inch is the ambient pressure) would indicate about 2-3 psi higher than at sea level. On the other hand, traveling from a high altitude location to sea level would result in an apparent loss of pressure of about 2-3 psi."

davidceder · 08-29-2020, 03:11 PM

So, it seems to me that the consensus on this forum has always been to get the rig weighed and then set the tire pressure according to the tire manufacturers table. Am I correct? That makes the sticker in the rig meaningless and contradictory to the philosophy of weighing the rig and setting the tires. I believe the sticker is mandated by the Feds and set by the manufacturer to match the max GVWR, it is a CYA. If you overload your rig the manufacturer is not at fault. It is in contradiction with the tire manufacturers.

So I weighed my rig and my front singles came in at 7220 or 3610 per side. My tire table set that PSI at 75 lbs for a single. I put in 85 as a safety factor. My rear duals came in at 14,580 or 7,260 per side. The tire table set that PSI to just above 85 lbs for a dual. I put in 92 as a safety factor. Unless I am doing something wrong that is the reason my fronts are lower than my rears. For those of you that wish to check my math I have Michelin XRV 235/80R22.5G. Please inform me if there is something I could do better. The rig rides hard enough, I really do not see a point in putting in so much more pressure than called for. If I should be doing that then I should not be weighing the rig and setting tires.

Podivin · 08-29-2020, 03:21 PM

I agree with everything said before. Also, I expect that if you were to check with the manufacturer of your TPMS system you'll find that it's guaranteed to be accurate +/- some percentage - something between 5% and 10% I'd wager. So even though they read in 1 pound increments they probably aren't guaranteed to be 100% accurate.