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> Class A Tire Pressure Question
chowhound
post Sep 18 2011, 09:58 PM
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I have searched through the many tire topics on the forum but not found any past discussions on this topic.

For years with cars and pick ups and motothome I have kept the tire pressure (cold) approximately 90% of maximum i.e. 40 p.s.i. on passenger tire with a 44 p.s.i max. 108 p.s.i. on motorhome with 120 p.s.i. max. Never have had any problems as a result.

I recently installed a TPM system on the motorhome, and it referred me back to the manufacturers specifications for load and pressure. it reccommended that I weigh the motorhome and put in the minimum pressure for the load per axle (making sure that weight per tire does not exceed the maximum weght for that tire range).

I haven't weighed the motorhome yet, has any one else? The second part of the question is that if the load turns out to be far less that the maximum for the tire, and you reduce the p.s.i. accordingly wouldn't you lose m.p.g.? If more p.s.i. means more carrying capacity and better m.p.g. why wouldn't you simply go back to 90% of max p.s.i. ?

Any help on this topic would be appreciated.
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John Blue
post Sep 19 2011, 08:52 AM
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Chowhound,

You are on the right track with air pressure. Our motorhome ask for 90 PSI in rear and 85 PSI in front. I run 95 all round and find it works well. We can pump up to 125 PSI as we run all Bridgestone steering truck tires with two steel belts in sidewalls and 12 more belts under the tread. One more tough tire. Cost lots of money but we have never had a tire problem yet. If we add more air up to 115 PSI the steering is a little on the light side and could be a problem on wet roads or if road has snow. Also we check tires each time we plan to move the motorhome. You could pick up a nail and would never know it.


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John
Brandon, Fl.
FMCA F-248693
Foretravel MH
Honda CRV tow
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RFCN2
post Sep 20 2011, 09:37 PM
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I have owned our current motor home for close to two years. I bought it used and the previous owner was very non-mechanical. I found out there are about as many opinions of the correct tire pressure as people I asked. Finally I went to the factory the last August. They referred me to the tag left of the drivers seat and said, follow the instructions on it. Since then the coach has handled better, although not bad before. So if you have a manufacture tag next to your drivers seat follow it, IMHO.


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Bob & Barbara
2002 Affinity
2013 Jeep Wrangler Unlimited
2013 Airdale Terrier
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Fitzjohnfan
post Sep 20 2011, 11:32 PM
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Yes, you should weigh your coach to determine the amount of weight you have on each corner, then determine the tire pressure from there, using the manufacturers specifications. The max PSI on my tires is 95lbs, but because of the weight of my coach, the correct pressure for my tires is 70lbs. I confirmed this on the michelin website, and on the sticker near the drivers door on my coach.

The Michelin website has lots of good info on RV tires, and I'm sure other manufacturers have similar info
(Michelin RV tire info

Another good reason th weigh your coach is to see if you are overwheight anywhere. I found that with all my tanks full (black, grey, fresh water and fuel) I'm overwheight by about 400lbs in the rear. Not a large amount and I can avoid this by dumping tanks regularly and shifting some contents around in the compartments, but it was educational.


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Chris G.
Westminster, CO
FMCA: F3508-S
1989 32' Southwind MH
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joez
post Sep 21 2011, 07:36 AM
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QUOTE
I haven't weighed the motorhome yet, has any one else? The second part of the question is that if the load turns out to be far less that the maximum for the tire, and you reduce the p.s.i. accordingly wouldn't you lose m.p.g.? If more p.s.i. means more carrying capacity and better m.p.g. why wouldn't you simply go back to 90% of max p.s.i. ?


Get your unit weighed (4 corner if you can) as soon as possible. The only correct way to set pressure is by weight. If you do not know the weight all you can do is set to maximum and hope you're not overweight. If you want to run more pressure than required after weighing you will get (theoretically) a rougher ride. We run at the manufacturer's recommended pressure + 5 pounds.
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abbygolden
post Sep 21 2011, 06:49 PM
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Interestingly enough - or not - the WH web site for my MH calls for 100 psi on the fronts and 90 psi on the rears. However, on the documentation that came with the MH and the tag on the driver's door, it states 90 and 80 respectively. I run somewhere between the two, my tires are about eight years old and I have never lost more than a pound a year, some years none at all. The tires still look nearly new. And yes, since they are Michelins and can be used up to 10 years, I have them checked yearly by a Michelin rep. I just wish everything I've ever owned could be this reliable.
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Fitzjohnfan
post Sep 21 2011, 09:27 PM
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QUOTE(abbygolden @ Sep 21 2011, 06:49 PM) *

And yes, since they are Michelins and can be used up to 10 years, I have them checked yearly by a Michelin rep. I just wish everything I've ever owned could be this reliable.

Just wondering where you heard/read that Michelins can last 10 years? I've always heard you should replace them after 7 years.


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Chris G.
Westminster, CO
FMCA: F3508-S
1989 32' Southwind MH
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abbygolden
post Sep 22 2011, 08:30 AM
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QUOTE(Fitzjohnfan @ Sep 21 2011, 10:27 PM) *

Just wondering where you heard/read that Michelins can last 10 years? I've always heard you should replace them after 7 years.


I'm guessing that since you asked that question you don't have Michelin as it is in their brochures and on their web site.

You are probably aware that how long you can keep your tires is a big item of discussion on all forums. Generally, most people feel that after seven years they should change out and get new tires. Some people feel it should be no more than five years. I prefer to defer to the manufacturer and follow his advice. The phrase "I've always heard" is nothing more than heresay and people's opinions. I'm not saying they aren't valid sometimes, but I still defer to the manufacturer.
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Kirk
post Sep 24 2011, 01:52 PM
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On the question of tire pressure, doesn't it make the most sense to follow the instructions of the tire manufacturer? The tag that is installed on the RV was put there based upon the maximum loading of the tires that were on the RV when it left the factory. It is a case of going to the maximum to assume that you will do the same. But once you own the RV the weights that they used have little to do with reality. Step #1 should always be to weigh the RV and get individual axle weights at a minimum and by wheel is by far the best way.

Once you have the weight on each tire the tire manufacturer's guide for the specific tire that you are running is the best answer. Following that will get the best combination of ride, tire wear and mpg. Harder tires do not mean better mileage, especially since the arrival of radial tires that are designed to have a specific footprint. It also means a hard ride as well as tire abuse because it prevents the designed flexing of the tire for bumps and things run over.

On the tire lifespan issue, the fact is that Michelin says that tires can last "up to 10 years" but it does so with the warning that each tire's use and history is the key factor. Both Michelin and Goodyear now manufacture tires designed specifically for use on a motorhome and those probably do outlive the previous designs, but both manufacturers also state that it is impossible to give an accurate prediction of tire life. They also agree that once you pass 5 years of age it becomes a case of probabilities and with each year older the likelihood of catastrophic tire failure increases.

Some owners do manage to run their tires for 10 years or even longer, but some of them also experience a blowout that will frequently do serious damage to the RV if at highway speeds and has even been the cause of a serious accident. Replacement of tires at any specific age is simply a case of playing the odds. How much is your safety worth?


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Good travelin !..............Kirk
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URL: www.adventure.1tree.net
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