Subject: Tire Air Pressure – Who Do I Follow?

[Paul Meehan]

Subject:  Tire Air Pressure – Who Do I Follow?

I have been RVing since the mid-70’s but new to motorized coaches and a definite newbie to anything diesel.  I have just joined FMCA and BAC.  Just finished reading Beaver tales.
Since the purchase of my “new-to-me” 2001 Patriot Ticonderoga in December I have more than appreciated this forum and all who participate by asking questions and most importantly providing answers and suggestions!  In the Jacksonville, Florida area I have yet to find an all-inclusive service provider that is comfortable working on my coach.  Thus far I find when they are working on the coach it is a learning experience for them and nothing happens quickly.
A day does not pass where I do not learn something new from this forum.  Thanks to all who make this invaluable tool available.
Sorry, now to the point.

I bought my coach with new ST727 Sumitomo tires installed.  On the Sumitomo website I came across specifications for this tire.  In past readings on the forum it has been stated that tire PSI is weight dependent.  The link below displays the MFG. specifications for my tire ST727 275/70R22.5.  When cleaning the coach last weekend I came across an interior coach sticker providing information on the same topic.  The coach and Sumitomo information differ greatly.  As a side note the dealer put 107 lbs. in all tires stating it is what he was comfortable with.  After reading the Sumitomo specs I increased the PSI up to 120.  I can certainly feel the harder ride.  I am hoping to receive guidance on how to proceed in determining the proper air pressure to run.  I have yet to obtain axle or corner weights.  Thanks in advance!
Paul

Sumitomo Tire Specs: http://www.sumitomotire.com/assets/products/medium%20truck/ST727ST717.pdf

Sumitomo specs prescribe:
Single – MAX PSI 120 – MAX load 7000 lbs.
Dual – MAX PSI 120 – MAX Load 6395 lbs.

Coach Specs:
GAWR            Weight       RIMS        Tire             PSI
Front         12,000 lbs.   7.5x22.5   275/70R     100
                   5,443 kgs   
Rear          19,000 lbs.   7.5x22.5   275/70R       90
                   8,618 kgs.   
            
GVWR   31,000 lbs. (14,061 kgs.)   

[Jerry Carr]

Paul have you had your coach weight done yet?
You need weight at each tire location, your dealer surely would not have done the weights as you rig would not have been loaded yet.
Once you are loaded with water and fuel and basement full you need to find a scale. Will you be going to the Seven Feathers Rally?
The rally master has a couple of vendors doing weights.

[Steve Huber Co-Admin]

Paul,
The pdf  file at this address shows the Sumitomo inflation guide based on tire location and weight.
Steve
http://www.irv2.com/forums/misc.php?postid=674839&threadid=69297&external_page=http%3A%2F%2Fwww.sumitomotire.com%2Fassets%2Fproducts%2Fcatalogs%2FCommercial_Truck_Catalog.pdf

[Edward Buker]

Paul.

One additional side note, when you get the 4 positions weighed, the tire position that has the higher weight on a given axle sets the weight and resultant air pressure for all tires on that axle.

Later Ed

[David T. Richelderfer]

Without axle weights or, better yet, corner weights, the best guidance is to play it safe.  Your tires' manufacturer prescribes 120 psi maximum [cold] per your message's text.  My best guidance would be to keep your tire pressures very close to 120 psi... UNTIL you get the corner weights and then adjust your tires' pressures per a manufacturer's chart.  Logically, with your tires' weight bearing capacity being 7,000 lbs (single) and 6,395 lbs (duel), compared to your coach's spec chart showing 12,000 lbs (single axle) and 19,000 lbs (duel axle), you have only 1,000 lbs and 1,645 lbs, respectively, of excess weight bearing capacity built into your tires.  Without the actual corner weights, this suggests to me you need to keep your tires very close to their 120 maximum [cold] psi to play it safe - and more so on the single axle.

Our coach had 295/80R22.5 tires all around when we purchased it.  I have not had the opportunity, either, to get corner weights, but I did get axle weights.  Our coach's steering axle weight prompted us to go to 315/80R22.5 on the frontend.  Moderate checking on both of the original tires near the tires' beads (within 3/4 in. of the rim) lead me to more promptly make the change.

[Gerald Farris]

Paul,
David is correct in that you should run the maximum inflation (120 PSI) in your tires until you have the opportunity to have the coach weighed at each corner. Axle weights alone will not give you enough information to properly set your tire pressures because very few Beaver coaches weigh the same on both ends of a axle. My coach weighs 1,000 lbs. more on the LR than it does on the RR, and 600 lbs. more on the LF than the LR.

Gerald   

[Paul Meehan]

Thanks for the responses.  Next step get the corner weights!

Jerry, I am sorry to say we will not be attending the Seven Feathers Rally.  I have a couple more years before I can head out that way.  This will be enough time to get the coach ready and for me to gain experience with it.
Steve, thanks for the link.  I had the single spec page for my tires.  Your link provided more details based on varying weights.
Thanks to Ed, David and Gerald as well! 

[Joel Ashley]

Our short Monterey is actually heavier than your rig, but I now run around 95 front, 100 rear.  The Toyo tire dealer went with 110 front, 100 rear, but Henderson's dropped the front for ride improvement at my behest but within safety numbers.  The old Goodyears came from Beaver at 110 all around, but RVSEF recommended 95 front, 100 rear.  So it varies from manufacturer to manufacturer, probably due to different sidewall builds, and from dealer to dealer.

Similar to Gerald's experience, our coach can be 900-1500 lbs heavier on one rear than the other side, and between 100 and 400 lbs different across the front axle.  Changes in loading practices and added devices and features/parts over the years causes the flux those numbers.

Check the RVSEF website for their weighing event schedule and see if you can get in.  But stay at 120 in the interim and put up with a little worse ride, and perhaps a bit of centerline wear.  Just don't wait years to get a four-corner weigh, when you actually could be running at lower numbers probably similar to your dealer's.

Joel

[Joe Rhea]

What does RVSEF stand for?
I have been unable to find a place in the Houston area that would give me individual wheel weights.
My previous coach was done at a FMCA rally in Claramore OKla.

[Steve Huber Co-Admin]

RV Safety Education.   https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwiA_aSo4qLOAhWF7iYKHbPNBIoQFggfMAA&url=http%3A%2F%2Fwww.rvsafety.com%2F&usg=AFQjCNEuxfcd1-wH-JTMOrydIXjVL5cRuA&sig2=OhlKBBDxIpFA_YIKxH0M-Q

Steve

[Joe Rhea]

Thanks Steve, Austin is definitely due able.
Good information

[Gerald Farris]

Joe,
You can probably get your coach weighed at each corner at the Escapee RV Club headquarters at Livingston Texas. Livingston is half the distance of Austin from Houston. However, you should call the Escapee headquarters before traveling to Livingston to be sure that the scales are there.

Gerald

[Joe Rhea]

Thanks Gerald will do.