Yet another tire pressure question

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fijidad

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Have our 36-foot DP in for servicing and the tech said they were going to set the tire pressure at 120, per the manufacturing tag behind the driver's seat. I said "isn't that the MAX. tire pressure?"...he said no, it's what the TP should be set to.

I'd read much before this experience and had set my TP at 80 based on front and rear weight and tire size.

Any thoughts on this?
 
Go back to what has worked for you in the past as long as it isn't below the tire manufacturers recommendations.
 
The 120 is wrong, that is the maximum pressure the tires are good for. Weight the rig and consult the tire manufacturers chart for the proper pressure.
 
Some people over on the FMCA forum are recommending +5% of the recommended max pressure.
 
From the stand point of handling, the tire pressure on the fronts should be set to the minimum pressure required for the actual load. To do otherwise would reduce the pneumatic trail which will reduce the "Self Aligning Torque" (SAT) which has an effect similar to reducing the positive caster.

https://en.wikipedia.org/wiki/Self_aligning_torque
 
tech said they were going to set the tire pressure at 120, per the manufacturing tag behind the driver's seat. I said "isn't that the MAX. tire pressure?"...he said no, it's what the TP should be set to.

The psi shown on the placard by the driver seat will be for the coach when it is loaded to its max capacity (GVWR). That is NOT the tire's max load pressure, which is embossed on the sidewall. [I think the latter is what Seilerbird referred to.]

If you have scaled weights that show your coach is loaded to less than its GVWR and each axle's GAWR, then you can safely use a lower pressure, which you would obtain from the tire manufacturers load & inflation tables. However, I am skeptical that the difference between the actual load and GVWR load would allow a 40 lb difference in psi.  That's an unusually large variation, though not inconceivable. I suggest that you re-visit the inflation table and make sure your 80 psi is correct for the load.

Your tire psi should be set at least 5 psi above the minimum for the loaded weight as shown in the inflation table. That allows for variations in load and ambient temperature, so that you need not be concerned on a daily or even hourly basis.
 
You need to find a new tech. He's clueless about this. That is NOT how you determine the correct tire pressure.

Increasing air pressure as the tire heats up is of no concern in this process. You set the tires to the correct pressure (according to a load chart) when the tires are cold, and you're done. The pressure increase as the tire warms up is figured into the cold set pressure by the tire manufacturer.

I set my tires to the correct pressures 3 years ago and have not touched them since. For my coach that's 110 psi in the steer tires and 95 psi in the rears. I've run them over 50,000 miles since then. Drives and rides like a dream.
 
Rodney Davidson said:
Be sure to remember that you will gain 10 to 15% in pressure once your on the highway for some time.

That isn't necessary to determine cold pressure desired, but with a TPMS also having a temperature readout, it certainly is a needed understanding to avoid changing tire pressure because of those pressure gains. Of course the tires are designed with that in mind.
 
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