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Author Topic: Tire pressure for motorhome before it can be weighed  (Read 2476 times)

rodzent@gmail.com

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Tire pressure for motorhome before it can be weighed
« on: July 07, 2015, 10:00:23 AM »
I recently purchased a 2006 Fleetwood Excursion 39S.  The dealer had new Michelin 275/70R22.5 J (XZA2 ENERGY) tires installed.  I found that the tire company filled all 6 tires to about 115-120 PSI.
I have been unable to weigh the vehicle so I want to go by the Fleetwood inflation chart until I can get it properly weighed.

Fleetwood Chart says: 
Front GAWR 12,000 LBS
Rear GAWR 19,000 LBS

Michelin inflation chart says with these tires and weights:
Front: 110 PSI
Rear: 85 PSI

My question is about the rear pressure.  Am I correct that I should drop the pressure from the 120 PSI it was delivered with to 85 PSI?  I am looking for some confirmation that I am correct before I make that big of a change.  (I am new at this so thank you for your comments.) 

Are the majority of this size coaches running 85-95 PSI in the duals?  (39 foot Class A Diesel pusher)

I am not near a scale so need to run on the charts until I can get to a scale.
« Last Edit: July 07, 2015, 11:40:52 AM by scottydl »

bucks2

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Re: Tire pessure for motorhome before it can be weighed
« Reply #1 on: July 07, 2015, 10:27:33 AM »
You are correct that you need to get a scale weight. How long are you going to drive before you do? If it's going to be a significant period of time you could, on an outside longshot, get some abnormal wear in the center of the tread pattern after 10,000 miles or so running at the higher pressure. Running whatever short trips you do until you can be weighed at the higher tire pressure will give you the possibility of a harsher ride, which IMHO is a good reminder to make it to the scale. Remember that a 4 (6) wheel position weigh is nice but a 2 (3) axle weigh will get you close enough for most rigs. If you have some unusual loading then work harder to get the 4 (6) wheel weigh sooner.

If 85 pounds turns out to be too low for whatever load you have you could possibly damage the sidewalls by excessive flexing, and in an extreme case even overheat the tires and cause damage.

Better to have too much air than too little. Remember too that many 38'-40' rigs run really close to their maximum weight capacity just in normal use. Err on believing you are heavy rather than light.

Ken

Tom

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Re: Tire pessure for motorhome before it can be weighed
« Reply #2 on: July 07, 2015, 10:28:05 AM »
Most RV dealers have no clue about tire pressures. When I picked our coach up from the dealer, their PDI tech told me he'd inflated all tires to 120psi and, when I checked them (cold) they were at 140psi, although the rims are rated at only 125psi. When I was able to get to a scale to weigh the coach and check inflation tables, the correct pressures were 85 front and 90 rear. I added a small margin (5 or 10 psi) and lowered the pressures accordingly.

Since we don't know which tires the Fleetwood chart is based on, I'd look at the Michelin inflation chart for the XZA2 and use the GAWR limits until you can get to a scale. Be sure to use the "dual" numbers for the rear.

FWIW we have a 38 foot Monaco Camelot DP with single rear axle.
« Last Edit: July 07, 2015, 10:37:00 AM by Tom »
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Gary RV_Wizard

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Re: Tire pessure for motorhome before it can be weighed
« Reply #3 on: July 07, 2015, 10:53:36 AM »
There will be a federal sticker by the driver seat with recommended default tire psi - use that if the tires are the same size as the original. Or use the axle GAWRs to estimate the pressure (as you did above). Yes, 85 psi is ok if that's what Michelin shows for that tire in a dual configuration and 19k lbs for 4 of them. Err on the side of too much rather than too little, though. And extra 5 or even 10 psi if fine.
Gary
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rodzent@gmail.com

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Re: Tire pessure for motorhome before it can be weighed
« Reply #4 on: July 07, 2015, 11:16:27 AM »
Thank you all.  I will lower the rear from 120 PSI  to 95 PSI  (85+10 to spare).

Rod


John From Detroit

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Re: Tire pressure for motorhome before it can be weighed
« Reply #5 on: July 07, 2015, 05:24:49 PM »
Given my choice of over or under.. i'd rather go OVER till I get to the scale.

Someone had a suggestion.

Chalk across the tred.. Drive a short distance and inspect the chalk

Worn off outside,, Not in the middle.. ADD AIR

Other way around.. Bleed some off

Evenly worn across tire: MEASURE PRESSURE AND WRITE IT DOWN.

Nothing adds excitement like something that is none of your business
My Home is where I park it.