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Old 05-22-2013, 07:51 PM   #1
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Air Pressure in tires?

Can anyone tell me what psi I should be running? I have heard different answers on this. I have a Thor Challenger 37 DT.

Thank you in advance Pete
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Old 05-22-2013, 08:14 PM   #2
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Max tire pressure cold. Either check early in the morning or late evening and not pulled around.

Mine call for 50 psi...
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Old 05-22-2013, 08:23 PM   #3
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The above is only true for a trailer.
The OP has a motorhome and the pressure on a MH tire sidewall is not the maximum pressure the tire should ever have. It is the MINIMUM pressure to support the MAXIMUM rating of the tire.
A MH that has not been weighed should use the chart on the sidewall of the MH and it is only correct if the MH is loaded to it's maximum weight ratings.
Right now I'm on a computer at work. I'll post the info from the tire manufacturers when I get my laptop set up.
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Old 05-22-2013, 08:52 PM   #4
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What Mr D said. There is no simple answer for a motorhome - it depends on the size of the tire and the actual load to be carried by that tire (or the axle load rating, if actual loads are not available.

Most motorhomes built in the last sevral years will have a federal weight placard on the wall near the driver seat. It gives information about weights and tires, including a "recommended" tire psi for front and rears. However, that recommendation is based on a fully loaded coach and many RVers don't run anywhere near that heavy.

So, Pecono, what size tires, and what are your actual weights on each tire position. And if you don't have those, what are the front and rear axle weight ratings (GAWRs)?
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Old 05-22-2013, 08:55 PM   #5
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The pressure on the sidewall of a Michelin RV tire and many others is not the "Maximum" the tire should ever have (unlike car tires) it is the minimum to support the maximum rated carrying capacity of the tire.

From the Michelin RV Tire Guide:
Quote:
"If you look at the tire's sidewall, you'll see the maximum load capacity allowed for the size tire and load rating, and the minimum cold air inflation needed to carry the maximum load."
From page 6 of the GoodYear RV Tire and Care Guide:
Quote:
"How much air is enough?
The proper air inflation for your tires depends on how much your fully loaded RV or trailer weighs. Look at the sidewall of your RV tire and you’ll see the maximum load capacity for the tire size and load rating, as well as the minimum cold air inflation, needed to carry that maximum load."
From TOYO:
Quote:

Inflation Pressure Safety Margin
Toyo Tire does not recommend an “inflate-to-the-load” policy for RV tires. Tires that are inflated to accommodate the vehicle’s actual loads do not have any inflation safety margin. Consequently, even a minor loss of air pressure will cause the tires to be under-inflated and overloaded. Toyo Tire’s policy is to observe (as a minimum) the tire pressure established by the vehicle manufacturer as indicated on the tire information placard. There are multiple reasons why a safety margin
(by inflation) makes sense:
• All tires lose about 1-1.5 PSI per month due to natural permeation of the tire’s internal air pressure through the tire’s rubber membrane.
• In the event of slow air leaks from punctures, an inflation “reserve” may allow detection and repair of the leak prior to reaching a dangerously low inflation level.
• A safety margin is prudent for users who are apathetic regarding tire inflation maintenance.
But then they go ahead and publish a weight/pressure chart allowing lower pressure for RV's!!

From the August 2010 Motorhome Magazine "Tread Carefully" tire article:
Quote:
The maximum load capacity allowed for the size tire and load rating and the minimum cold air inflation needed to carry that maximum load are located on the tire’s sidewall.
Most tire manufacturers publish a RV tire guide that shows how to weigh you rig and what to do afterward with the info.
We don't know what tires you have but above info is available on the Internet. I have hard copies of the Michelin, GoodYear and TOYO guides at home.
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Old 05-22-2013, 09:18 PM   #6
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Below is the link to a GY inflation chart.

http://www.goodyearrvtires.com/pdfs/rv_inflation.pdf

The label on the wall of my RV has 80 psi for all tires, but my RV is a 1999, and for my tire size the GY has a different listing for tires made after 02-2006, and moved the pressure up to 90 psi. I have not had a chance to weigh my RV yet so I am going with the 90 psi.

Tire size 245/70R 19.5

Front GAWR 7000
Rear GAWR 13500
GVWR 20500
GCWR 26000

Comments are welcome I am all new to this. Hope to weigh it soon.
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Old 05-22-2013, 09:36 PM   #7
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Quote:
Originally Posted by Mr_D View Post
The above is only true for a trailer.
The OP has a motorhome and the pressure on a MH tire sidewall is not the maximum pressure the tire should ever have. It is the MINIMUM pressure to support the MAXIMUM rating of the tire.
A MH that has not been weighed should use the chart on the sidewall of the MH and it is only correct if the MH is loaded to it's maximum weight ratings.
Right now I'm on a computer at work. I'll post the info from the tire manufacturers when I get my laptop set up.
I think you are misinterpreting the tire pressure requirements. The pressure on the side wall IS the minimum cold pressure needed to carry maximum load, it is also the max pressure the tire is rated for. It sounds like your saying its ok to inflate above the rated psi when tire is carrying max weight, this is not correct you should never exceed that psi with a cold tire. If this is not what you are saying then I humbly apologize, but that's kinda what it sounds like what you putting out there.
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Old 05-23-2013, 08:56 AM   #8
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Thanks to all who answered thread.
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Old 05-23-2013, 09:05 AM   #9
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I have the tire info and the wall card info. Michelin tires, tire info- 235/80 R 225 XRV max load single 4675 110 psi cold, max dual 4410 110 psi cold. Wall card- front gawr 8000 lb single cold 90 psi, rear gawr 15000 lb dual cold 90psi.

If I go by wall card I want to inflate to 90 psi cold ?

Again thank you for all your help.

Pete
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Old 05-23-2013, 09:58 AM   #10
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Just got four new rear tires on my coach, XRV 235/80 R225. The coach wandered really bad on the way home, acted like wind was blowing me all over. However the wind not blowing at all.

The tire dealer had put 115 pounds pressure in all my tires. I keep my tires at 90lb as per the weight of my coach and the Michelin tire pressure chart for my size tires. I add 5lb for some leeway.

You have to weigh your coach and go to the tire makers web page and see what they recommend for the weight on your tires.
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Old 05-25-2013, 11:05 AM   #11
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Originally Posted by Arch Hoagland View Post
Just got four new rear tires on my coach, XRV 235/80 R225. The coach wandered really bad on the way home, acted like wind was blowing me all over. However the wind not blowing at all.

The tire dealer had put 115 pounds pressure in all my tires. I keep my tires at 90lb as per the weight of my coach and the Michelin tire pressure chart for my size tires. I add 5lb for some leeway.

You have to weigh your coach and go to the tire makers web page and see what they recommend for the weight on your tires.
I think I read someplace all tires wander until they are scrubbed in after a 100 miles or so. Please correct me if Im wrong.
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Old 05-28-2013, 02:53 AM   #12
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Originally Posted by SeattlePirat View Post
I think I read someplace all tires wander until they are scrubbed in after a 100 miles or so. Please correct me if Im wrong.
You are correct according to a friend of my who drives over the road for a living.

However extreme over pressure will also cause problems with stability.
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