Community Forums

Tomvg · 03-26-2022, 02:22 PM

I’m curious how much your tire pressure goes up when your driving. I have a TPMS system, and even on a cool day, my pressure will start out at 100 pounds. In about 1/2 hour or so some of the pressures will be up to as high as 117 to 120 pounds. That seems to me quite high, when the temperature for the tires is still around 70 degrees. Let me know if this is normal.
Thank you, Tom

twinboat · 03-26-2022, 02:28 PM

Yes it's normal and happened before you installed the TPMS.

Under inflated tires get hotter and cause higher temps.

nehog · 03-26-2022, 02:44 PM

Initial tire pressure:

1. Weigh your coach. Determine the per-wheel weights.
2. Get the weight to tire pressure chart from your tire brand and model.
3. Inflate based on the chart. I add about 5% personally.

If you find your tire pressure rises too much from cold to warm, it is possible your initial pressure is too low for the weight/tire combination. So do it properly.

FastEagle · 03-26-2022, 02:56 PM

Excerpt from USTMA manual page #44.

https://www.ustires.org/sites/defaul...uckTires_0.pdf

"Inflation pressure recommendations may a be determined based on the tire manufacturer’s specifications, which define the amount of inflation pressure necessary to carry a givenload. These inflation pressures may differ from those found on the vehicle tire placard or certification label."

"However, never use inflation pressure lower than specified by the vehicle tire placard, certification label or owner’s manual. Nor should inflation pressure exceed the maximum pressure molded on the tire sidewall."

Usually the tire manufacturer will provide an approximant increased PSI value for tires warmed from road use. It can be found in their truck tire data book/PDF files.

theroc · 03-26-2022, 03:05 PM

To answer your concern directly:

Yes, that sounds absolutely normal. Commercial truck tires are designed and engineered to take load, temperature, and speed variables into account. Therefore, a tire may seem overinflated at 125 psi but they are designed to take that 25% variable into account.

Load inflation tables are typically based on an ambient temperature of 70°. Therefore, if you've already determined that the proper pressure for your particular weight is 100 psi "cold" pressure (or before being run on the road), and assuming that you started rolling when the outside temperature is around 70°, then it is perfectly normal to see 120 psi or even more.

As has been said, do not lower psi when the tire has been rolling or the outside temperatures are very high. If you've correctly determined and have the proper "cold" psi, then you can essentially disregard the high temperatures showing on your TPMS while you are underway.

bentjm · 03-26-2022, 03:11 PM

Look at rvtiresafety.net - tireman9's website.

Lot of good information there. I learned a lot about the fallacy of measuring tire temps with an IR thermometer.

An increase of pressure from 100 psi to 120 psi indicates that the INTERNAL air temperature has increased by 40F. That increase cannot be measured from the outside.

Crasher · 03-26-2022, 05:01 PM

Most are saying a 20% increase in 1/2 hour is normal with a constant 70 degree OAT. I disagree. A 20% increase over the course of several hours is normal however, 4-5% of the increase is due to the OAT increasing 20-25 degrees. In your case, after several hours of rolling resistance and OAT increase you could see 25-30% increase in pressure. The tire can accept that, but I would want to know why. As others have suggested, are your tires inflated for the load they are carrying. My front tires loaded to 7300# each will rise from 118 to 135 psi on a cloudy day when the air temp remains steady. They will increase to 142 if the OAT increases from mid 60's to upper 90's. I have fount that I get a 15% increase in pressure from rolling resistant and the rest is from OAT increase. I say this from what I have observed over the years of pressure monitoring, but may not be worth more than what you paid for it. Be safe.

Tomvg · 03-26-2022, 05:25 PM

Thanks for the info on the tire pressure. Before I got the TPMS system, I always check the pressure in the morning before we headed out for the day. Bumped them when I stopped, but never check the pressure. Now I find myself looking at the display all the time. I appreciate all the feedback, so I’m good with it