Tire Inflation Confusion

[Roscott]

Hoping somebody can set me straight. I've read multiple threads about tire inflation and have referenced the tire manufacturers inflation charts in order to determine optimum pressure based on tire and rig weight (I have front and rear weights only at this time -- not 4 corners). I have 2 Firestone FS 560 on left rear duals (used to be on front until I had alignment and dealer suggested moving to the rear). I have Bridgestone R250 ED on right rear duals and front. My rig weights are 9500 front and 16500 rear. Tire size is 275/70R22.5. The Firestone and Bridgestone charts state my inflation should be 120psi @ 6395 lbs at the rear for max tire load...but my rig weighs in at 16500! Bridgestone states the front should be 120psi @ 7000lbs for max tire load...rig weight is 9500 at the front!

Am I looking at the wrong charts or am I interpreting things incorrectly....or both? Does the max load take into consideration spreading the weight across multiple tires? In my case I would need to look at 9500 divided by 2 for the front and 16500 divided by 4 for the rear? Confused....

At the moment, I have all 6 tires at 110psi.

http://www.trucktires.com/bridgeston...ckDataBook.pdf

http://www.firestonetrucktires.com/p...3_HiRes_r3.pdf

["007"]

Different tires will make confusion.
I would stick with one table for size and inflation.
Have you weight it with you full load as you are using it, full fuel. stuff loaded and water you will be carrying?
Here is a thread by Tireman that might help you and I would try the Michelin table to cut the confusion.

[Roscott]

Sorry, yes, it was loaded.

[DieselTech39]

Originally Posted by Roscott

In my case I would need to look at 9500 divided by 2 for the front and 16500 divided by 4 for the rear?

Short answer is yes. The maximum rating is per tire @ the specified PSI. Each tire supports only a portion of the total weight applied to the respective axle. Get your 4 corner weights and adjust pressure based on those.

[JFXG]

Originally Posted by Roscott

.......Am I looking at the wrong charts or am I interpreting things incorrectly....or both? Does the max load take into consideration spreading the weight across multiple tires? In my case I would need to look at 9500 divided by 2 for the front and 16500 divided by 4 for the rear? url]

Hi, Roscott..... Yes, you 're misinterpreting the charts, I believe. The weights given in the chart are per tire, so you have to apportion the load per tire, as in your final example.

As a rule of thumb, on a class A like yours the individual pressures in the four rears will be somewhat lower than the two fronts. Not always, but usually.

[cvbdsl]

Yes;
Each front tire only supports (roughly) half the weight of the front. So half of 9500lb is 4750lbs for each front tire so you are well under the max load.
Same thing for the rear duals, divide the rear axle weight by 4 so each tire supports 4125Lbs.
Adjust your tire pressures accordingly based on the manufactures charts.

If you get the exact corner weights then adjust to the correct pressure.

Chris

[wa8yxm]

Front axle is 2 tires normally so the weight carried by each tire, if you are perfectly balanced is 9500/2 or 4375 pounds.

I would inflate to the proper perssure per the cart and add 5 PSI for safety, Visually inspect and add more to one tire if needed (5 psi tops)


For the rear, you normally have 4 tires and they are DUALS so divide by 4 and use the dual chart for inflation.

ASAP get side (4-corner) weights and adjust per charts.

Again I like to add 5 PSI .

[Roscott]

According to a Bridgestone chart that lists more weight/psi values than the other chart I was looking at, it appears 85 psi is the number for both front and rear (with 5 psi added for safety). At least until I get the corner weights. Does this sound right? If so, I'm way over inflated at the moment.

If you can read the chart...the first column with weight values represents 85 psi and it goes up 5 psi as you move across the grid. So, the lowest weights represented are still higher than what I would need...but that's where the chart starts.

[JFXG]

Originally Posted by Roscott

According to a Bridgestone chart that lists more weight/psi values than the other chart I was looking at, it appears 85 psi is the number for both front and rear (with 5 psi added for safety). ........

Yup..... looks good! 85 psi will be fine. And, you'll notice a remarkable improvement in the ride!

[Roscott]

Thanks for walking me through this everyone!

[Pverderame]

I have a 2008 newmar baystar 33'. Trying to get the proper tire pressure for front and rear. Tire is sumitomo 245/70r. 19-5. If some one could help me I would appreciate it. I'am new at this.

[montiem]

The easiest way is to inflate the tires as per the axle weight, a coach with 16000 lbs. axles will inflate to a weight of 8000, the rear the same, what ever the axle weight stated on the placard behind the drivers seat. My fronts are at 120, duels at 90, tag at 80, that is with 5 # safety measure. The weigh changes all the time, with fuel and water, so I took the advice of the manufacturer use the max axel weight and everything is ok, I hope

[Dr4Film]

Originally Posted by Pverderame

I have a 2008 newmar baystar 33'. Trying to get the proper tire pressure for front and rear. Tire is sumitomo 245/70r. 19-5. If some one could help me I would appreciate it. I'am new at this.

Use the attached document to help you establish the proper tire inflation for your RV and brand of tires.

Dr4Film ----- Richard

[capnqball]

You will need to get the actual weights on each axle first before we can advise further. Better, get the weights on each corner. You can do this by going to a weight scale along the highway, one that is not 'open' for the trucks at the time. The scale readouts are usually still on when the scales say 'closed'. At least thats my experience here in Oregon and Washington. Some locations are wide enough that you can first weigh one side and then weigh the whole coach (each axle separately of course). The difference in the respective readouts will give you the weight on the corner you couldn't get on the scale separately. Having found the values you can then go to the Sumi website and get the proper pressures for your tires. And as stated above, allow 5 psi as a fudge factor to your tire pressures. Hope this helps. We were all newbies at one time in our past. Good luck and happy travels.