Tire Pressure Help

[ktmnoel]

I guess I'm not as smart as I thought I was. I just don't understand the tire pressure chart.

My front axle is 5560 lbs and my rear is 9500 lbs. I have 225/70R 19.5 XZE Michelin tires. Dual in rear.

How do I read this chart? Michelin North America RV Load & Inflation Tables

Do I divide the axle weights by 2 for each side?

Some one please educate me.

Thanks.

[Dixieray53]

I always use the factory label on my coach...110 psi front...95 psi rear..
That chart makes my head hurt...Peace...D

[DriVer]

Quote:

Originally Posted by ktmnoel Do I divide the axle weights by 2 for each side? Some one please educate me. Thanks.

For SRW (1) applications the inflation and weight only apply for a single tire on the axle end. Both tires together (2) on the axle comprise your GAWRF (Gross axle weight rating front). Could be steer or drive axle.

For DRW applications the inflation and weight apply for dual tires (2) on the axle end. All the tires (4) when inflated on the rear axle comprise the GAWRR (Gross axle weight rating rear).

[Mr_D]

Also, all pressures must be the same across an axle and also must be for the heaviest position.

[DriVer]

Quote:

Originally Posted by Mr_D Also, all pressures must be the same across an axle and also must be for the heaviest position.

I subscribe to that as well however you will find some people out there that will feel that individually adjusted tire pressures depending on corner weight is what they inflate their tires to. I would rather inflate to the larger weight and apply the same pressure to the opposite tire.

[Mr_D]

Quote:

Originally Posted by DriVer I subscribe to that as well however you will find some people out there that will feel that individually adjusted tire pressures depending on corner weight is what they inflate their tires to. I would rather inflate to the larger weight and apply the same pressure to the opposite tire.

tire manufacturers recommendations in their guides. They specifically say to take the heaviest end and use the charts for that weight for all tires on that axle.
From Michelin's RV Tire Guide:
REMEMBER: For control of your RV, it is critical that the tire pressures be tha same on both sides of an axle. (emphasis from Michelin)

[DriVer]

Quote:

Originally Posted by Mr_D REMEMBER: For control of your RV, it is critical that the tire pressures be tha same on both sides of an axle. (emphasis from Michelin)

10-4 ...

[Richardrky]

I am confused also!
I weighed my motorhome at a farm co-op but could not weigh each tire position. The front weighed 7160# and the rear weighed 12862#.
If I divide these weights by 2, I get @3580# for each front tire and 6431# for each rear tire.

Using the Michelin tables, I read it as saying 235/80R22.5 XRV tires would only need between 70 and 75 psi for each tire.

The Newmar label says to inflate both front and rear tires to 110 psi.

Who do I believe?
I just can't believe these numbers are correct. I think one is too low and the other too high. Can anyone shed some light on the subject?

I realize this subject has been covered a lot but I am still confused. Maybe it's just old age.
Thanks

[Jackm]

Richardrky,

Assuming you used the charts shown on the web page below and that your rig's weights are accurate, I would go with a recommended pressure of around 75 psi. Bear in mind, in most cases, the heavier your rig, the higher the recommended tire pressure. In your case, it looks like you're travelling light. However, to improve your gas mileage, I would probably put in 80 psi since there's no risk of over inflation at those levels.

Michelin North America RV Load & Inflation Tables

It's not you. I've stared at those charts for hours trying to make sense of the recommended pressures. Now, I just follow their suggested pressure levels (give or take 5%).

Jack

[RVNeophytes2]

Quote:

Originally Posted by Richardrky The Newmar label says to inflate both front and rear tires to 110 psi...

I believe that pressure is only good for the maximum certified vehicle weight, in the tires used for certification.

For actual usage, you've done the correct thing: using manufacturer's data, you've found the correct pressure for the actual rig weight, as you use it.

Michelin says you should inflate to 71 up front, 72 in the rear.

To verify that is the correct cold pressure, check the surface temp of the sidewalls after some highway driving: correctly inflated tires will be 110-120F. If temps are more than that value, add air 5 psi at a time, recheck. As you add more air, the tires will run cooler.

But, if the scales are correct, you should get prefect temps, right away.

[DriVer]

Quote:

Originally Posted by Richardrky The Newmar label says to inflate both front and rear tires to 110 psi. Who do I believe? I just can't believe these numbers are correct. I think one is too low and the other too high. Can anyone shed some light on the subject? I realize this subject has been covered a lot but I am still confused. Maybe it's just old age.

Richard, 110 psi as placarded by Newmar ??? That's insane! There is no way that you have 110 PSI of GAWR (front) on your motorhome. If your front axle scaled at 9350 pounds, "Yes" 110 psi or air would be required. Workhorse has only made available an 8500 optional front axle SPID and no more on a W22. If you were to inflate your front axle to the Gross Axle Weight Rating (GAWR) you would need to have about 97.5 psi per tire.

You never want to exceed the GAWR for the axle at any time therefore the OEM instruction to inflate your tires to 110psi is both technically flawed and diminishes your ride quality. On my rig I run 95F and 90R. Even these pressures are a little high but I would rather have a little more air than exactly what I need or less. Less air than you need is never a good thing.