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Old 07-20-2016, 12:05 AM   #1
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Tire pressure

I know there's been lots of posts and good information about RV tire pressure and safety issues. Read every one I could find, but still have a question for the experts.
We have a 2007 Fleetwood Expedition 38L that we purchased used in December 2015 and are 6 weeks into a six month "once around"
New tires were part of the purchase, they are Michelin XZA2 Energy 275/70R 22.5
We have not yet been able to weigh 4 corners, but did get Cat truck scale axle weights just last week.
Front 9100 Rear 17880 Gross 26980
Fleetwood specs are
Front GAWR 12000
Rear. GAWR 19000
GVWR 31000
The Fleetwood
"sticker pressures" are listed at 115 and 95 respectively. Which is what I've been running up til now. Cold readings @ 20 C.
Using a formula of axle weight +5% /2 = 4776 front.
The Michelin chart lowest number is 4940 which give a pressure of 85 psi, adding 5psi to that only gives me 90 psi which seems low to me.
For the rear, axle weight + 5% /2 = 9387 rear
Michelin chart lowest number is 9710 which gives a pressure of 85 psi, adding 5psi gives me 90 psi once again.
Inflation at 115 and 95 "looks ok" about 4K miles so far and no unusual wear noted. We have a TST pressure /temp monitor system that I watch carefully
Not sure I'm comfortable reducing pressure dramatically.
Suggestions or recommendations would be welcomed.
Thanks all.
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Old 07-20-2016, 04:02 AM   #2
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We are In the same boat. We have the same tires on our ´05 discovery. Our weights are low enough that we are at the bottom of the pressure chart.
Keep in mind the consequences of running too little pressure (tires heat up and can cause premature failure) versus too much (Coach tends to wander and handle a little squirrely). We run ours about 100 psi all around. Coach handles fine at that psi.
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Old 07-20-2016, 04:21 AM   #3
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I own a Newmar Kountry Star 39 foot 100 pouds in front and 95 in rear
28,775 the weight of my coach
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Old 07-20-2016, 06:36 AM   #4
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My 2006 Discovery has the following weights when fully loaded:

8,040# front axle
17,400# rear axle
25,440# total

I run 90 PSI in all of my 275x70x22.5 tires, which coincidentally is what the "Sticker" indicates.
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Old 07-20-2016, 06:35 PM   #5
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As long as you are confident your scaled weights are right, I would lower to 90 psi. The "factory" settings are for the axles when each is loaded to its GAWR, but you aren't anywhere close to that. If you want some extra margin, go with 95 psi.
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Old 07-21-2016, 08:03 AM   #6
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FYI, you'll not find a tire mfgr. that recommends running less pressure than the tire placard in the vehicle. Over 90% of tire failures are the result of underinflation/overloading at some point. This is due to excessive heat buildup from sidewall flex.
Goodyear says this about RVers seeking a more comfy ride:
"Tire pressure should never be reduced below the vehicle manufacturer's recommended levels to support load conditions in order to improve the ride quality of a vehicle. The difference in ride quality is not significant."
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Old 07-21-2016, 02:00 PM   #7
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True enough re their "recommendation", but they also provide the info for DIY (the same info they provide to RV makers to use). They "recommend" that you follow someone else's psi advice, so that the tire maker has no liability for the recommendation. Good lawyering, but not helpful.

It's not much difference than the engine makers position on extending oil change intervals. They give out a pretty much fail-safe time & mile interval and refuse to recommend anything longer. But if you ask about using oil analysis and other more advanced maintenance techniques, they say "sure you can". But they don't tell you how to do it or what is acceptable, cause they want YOU to assume the liability if anything goes wrong.
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Old 07-23-2016, 09:48 PM   #8
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Update

Thanks for input. Decided to lower tire pressure on the front end by 5psi. Drove about 150 mi today and performance, control, ease of handling, comfort of ride seemed to be noticeably improved. This was a rain day all the way, so we will see how it does in dry conditions on Monday
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Old 07-23-2016, 11:03 PM   #9
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Ray is correct in his post.

Tire manufacturer inflation pressure options are always directed at the vehicle manufacturer, they are the only ones that can properly set recommended inflation pressures for the vehicles they build under the guidance of FMVSS.

There isn't any restrictions against increasing tire pressures above what the vehicle manufacturer has recommended. However, tire industry standards are very consistent in supporting the vehicle manufacturer's recommendations for Original Equipment tires and like sized replacements. DON'T use less than what the tire placard, certification label or owner's manual says to use.
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Old 07-28-2016, 11:04 PM   #10
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Thanks for responses. One note on sticker pressure from the RV manufacturer, it's my understanding that their recommendation is based on fully loaded GWAR.
Once actual front and rear axel weight has been measured, then using the tire manufacturers recommendations is the way to go.
I also took our RV for an alignment check to Bauer Built Tire in Rochester MN. This past Wed
Very Customer friendly, professional , and responsive. Had us in for service same day,( even after a reschedule on our part) about an hour including measurement and adjustment for < $150. Have to give recognition for great Customer service.
Found Toe adjustment significantly out alignment
Now with readjusted alignment and slightly reduced pressures -using tire charts- ride, handling are much improved.
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Old 07-29-2016, 10:12 AM   #11
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Quote:
DON'T use less than what the tire placard, certification label or owner's manual says to use.
In the absence of any more specific load information, that's good advice. However, the RV manufacturer has no idea what weights you will actually carry, so he must assume worse case (fully loaded) when he creates the recommendation. Anybody who gets actual weights is well within safe guidelines to use the tire maker's load-inflation tables, but then you must shoulder the responsibility for getting the weights and reading the table correctly.
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Old 07-30-2016, 12:47 PM   #12
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Quote:
Originally Posted by Gary RVRoamer View Post
In the absence of any more specific load information, that's good advice. However, the RV manufacturer has no idea what weights you will actually carry, so he must assume worse case (fully loaded) when he creates the recommendation. Anybody who gets actual weights is well within safe guidelines to use the tire maker's load-inflation tables, but then you must shoulder the responsibility for getting the weights and reading the table correctly.
That's an owner's call. Tire industry standards for vehicles built under the guidance of FMVSS are very consistent in their recommendations to never use less inflation pressures than provided by the vehicle manufacturer's for OE tires or any like sized replacements.

Some of the major providers of MH replacement tires DO NOT recommend using inflation pressures equal to the load carried even if they are above the minimum requirements on the tire placard. Because? There is no room for error and in an ideal situation there is zero load capacity reserves.
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Old 07-30-2016, 12:52 PM   #13
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Quote:
Originally Posted by FastEagle View Post
That's an owner's call. Tire industry standards for vehicles built under the guidance of FMVSS are very consistent in their recommendations to never use less inflation pressures than provided by the vehicle manufacturer's for OE tires or any like sized replacements.

Some of the major providers of MH replacement tires DO NOT recommend using inflation pressures equal to the load carried even if they are above the minimum requirements on the tire placard. Because? There is no room for error and in an ideal situation there is zero load capacity reserves.
From our owners manual:
Quote:
Industry Changes
The tire industry, as a whole, has changed its traditional stance on adjusting cold tire inflation pressure for RV tires installed on recreational vehicles and busses. Previously, tire manufacturers supported a policy where tire inflation could be adjusted according to the actual loaded weight of the vehicle. Now, the major tire manufacturers recommend that medium duty truck tires be maintained at the pressure that corresponds to the Gross Axle Weight Rating for the axle to which they are mounted. To make this recommendation uniform across the industry, tire manufacturers strongly urge the consumer to keep all tires inflated to the pressures recorded on the Federal Tire Label.

Tire Inflation
Country Coach recommends that the cold tire inflation pressures should at all times be maintained at the inflation pressure(s) recorded on the Federal Tire Label. There are no acceptable circumstances where tire inflation pressure(s) should be reduced below that pressure recorded on the Federal Tire Label.
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Old 07-30-2016, 09:44 PM   #14
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Tire pressure

The Michelin Website has RV tire pressure recommendations with specific information for their tire types, size, and axel weight. I am using their recommendations +5% as a safety factor.
Here is a link to their website Michelin RV Tires | A Better Way Forward › load-and-infl...
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