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Author Topic: question about Motorhome tires...  (Read 3681 times)
bevans6
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« on: August 03, 2010, 06:45:57 PM »

Reading the FMCA magazine today I noticed that the big class A 42' Winnebago they were reviewing came with 275/80R 22.5 LRH tires.  I checked out the axle weight - 13.5K lbs as tested, GAWR of 14,320 LBs.  That is way higher than I have with my 12R 22.5 tires, so I looked up the tire weight ratings for the firestones I run (just because I happen to have that chart handy) and their 275/80R 22.5 load range H tire is only rated to 13220 on a single axle, way under the weights of this coach.  So I have to ask - what are these people thinking?  Do they really run these tires so loaded on purpose?  What is the thought process going on here - and yes, serious question, I really want to know if I am missing some subtle point.

Thanks, Brian
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RJ
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« Reply #1 on: August 04, 2010, 12:22:23 PM »

Brian -

Boy, the liars-for-hire would have a field day with this one if a front blowout fatally injured someone!

Winnibuggy could kiss their assets good-bye!


Scary!


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kyle4501
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« Reply #2 on: August 04, 2010, 12:40:17 PM »

Dad's Airstream motorhome (diesel pusher on a freightliner chassis) is so close to the stock tire weight limit, that if he fills the fresh water tank, he is over the max for the tires. & that is total axle weight - not even looking at actual side to side.
His solution was to increase load capacity by upgrading to a larger tire that has a higher weight capacity.

We didn't suspect there was a problem until after a friend with the identical motorhome kept blowing out the curb side inside dual. I got dad to weigh his & it was simple math from there.
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Lee Bradley
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« Reply #3 on: August 04, 2010, 01:41:40 PM »

This is one of the reasons I have a bus. S&S are built on truck frames that are sized to carry the completed motor home. Quite often they are overloaded when you load your food and clothes. 
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robertglines1
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« Reply #4 on: August 04, 2010, 02:00:26 PM »

this is a general industry practice to get by as cheap as possible..for the 40 yrs I have been involved in it Thur 5Th wheels etc..just enough tire to carry empty weight..but for a option you can get larger weight carrying tires..personal observation only from a former RV dealer....usually when one of the marginal tires fail it takes other tires with it because there is no safety factor built in...Why=$
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« Reply #5 on: August 04, 2010, 02:16:08 PM »

I monitor many of the Yahoo motorhome groups.  Many manufacturers have a BIG problem with front axle weight.  Here is a post from the American Coach group:

Quote
I own a 2007 Eagle 42F with a full wall slide and full tile floor. This model
is definitely one of the coaches that have the overweight front-end issue.

I just spoke to Kim at Spartan Chassis about their current program to upgrade
the 14,600 lb front-end to a 16,600 lbs.

He stated: The upgrade would consist of a complete removal of the current front
suspension and replace it with the upgrade.

The items would include:
315 x 80R x 22.5 Michelin tires [replacing the standard low-profile 22.5]
9 in. rims [replacing the 8.25 in.]
Disk Brakes [replacing the drum breaks]
as well as some other supporting components.
Upgrade includes certification sticker for 16,600 lbs.

There is currently an 8 week leadtime.
$1000 deposit at time of scheduling upgrade
Total Cost: $18,995
Cost includes Spartan retaining all components including tires.
If you want to keep your tires the cost is $200 per tire
Repairs must be completed at Spartan in Charlotte, Michigan
Estimated time needed to complete repairs: 1.5 days

Quite a few of the "factory manufactured Prevost" conversions have the same problem

Jim
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Jim Shepherd
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« Reply #6 on: August 04, 2010, 02:28:06 PM »

I assume you are talking about the front axle? Duals are rated to carry even less load per tire.

My HSL tire chart shows a weight rating, for two 275/80R 22.5H  tires on a single axle, of 13,880 lbs.

It all depends on the amount of stuff in the RV "as tested"??

On reading road tests in Motorhome Magazine it is very obvious that most S&S are rated for very little useful load and also that they are routinely overloaded by oblivious owners. Blowouts are a common complaint to the Tech Editor.

It is also obvious that the manufacturers do this to save money. The construction and engineering quality are criminally shoddy.

Almost as bad, to me, is the ridiculous rear overhang which not only makes them squirrely to handle and drag the rear but grossly overloads the rear axle, especially on rough roads.
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Len Silva
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« Reply #7 on: August 04, 2010, 02:50:00 PM »

I was reading an RV review a couple of years ago that Showed a Bluebird Wanderlodge with less that 1000 pounds of carrying  capacity.  Even bus converters have to be careful with granite and tile and other heavy materials.
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« Reply #8 on: August 04, 2010, 02:55:55 PM »

the target buyer of the sticks and staples is generally more concerned with glitz and price than build and weight carrying capacity----until they are on the side of the road with a several thousand dollar incident..If I may comment that from my understanding most sticks and staples are designed for a total life of 100,000 miles.(came from a factory rep).and from experience that's probably rite.The newer Prevost at Vantare come with a 18,000 front axle with 365 tires on them..I have granite floors and slides and my front axle weight on my 89 XL Le Mirage is 11,100 lbs loaded full of liquids and trip ready..
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Sean
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« Reply #9 on: August 04, 2010, 05:16:30 PM »

Reading the FMCA magazine today I noticed that the big class A 42' Winnebago they were reviewing came with 275/80R 22.5 LRH tires.  I checked out the axle weight - 13.5K lbs as tested, GAWR of 14,320 LBs.  That is way higher than I have with my 12R 22.5 tires, so I looked up the tire weight ratings for the firestones I run (just because I happen to have that chart handy) and their 275/80R 22.5 load range H tire is only rated to 13220 on a single axle, way under the weights of this coach. 


AFAIK, neither Firestone nor its parent Bridgestone makes a current tire in this size.

The Goodyear G670RV, which is a dedicated motorhome tire, in that size and LR, is rated at 14,320 for an axle with singles, and 27,720 for a dualed axle.  That gives a coach GVWR of over 42,000 lbs for a 2-axle coach, and over 56,000 lbs for a tag-axle model.  Hard to believe a fiberglass 42' rig will even come close to those weights.

Sounds to me like the GAWR is exactly the load rating of the tires, so that's probably the controlling factor.  Remember, GAWR is not the axle weight, it's the total axle capacity.  The actual weight is probably much lower.

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com
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bevans6
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« Reply #10 on: August 05, 2010, 07:35:34 AM »

I don't know for sure if Firestone actually makes a tire in that size, but my load/inflation chart from Firestone has that size in it, so I just looked there, which was very sloppy of me.  Today I took the time to look for the load inflation chart for Michelin XZA3 tires, and Sean is correct that the GAWR for the front axle is exactly the maximum rated load for the two tires, at maximum inflation.  Still only 800 lbs headroom between "as tested" and ultimate load capacity - that is only 5% or thereabouts. All their load capacity - close to 10,000 lobs in fact, is heavily biased towards the rear axle pairing, drive and tag, so maybe the long overhang is a good thing!

Cheers, Brian
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kyle4501
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« Reply #11 on: August 05, 2010, 08:04:11 AM »

Whenever a friend or coworker asks me what I think of the RV they are looking at, I'll point out the "stuff capacity". When I tell them it is close to overloading the tires, their usual response is one of denial that that really matters & that cost of the unit is more important. They'll even insist the manufacturer can't have built it that way because "the government won't let them".  Shocked   I still haven't figured out where they get that idea.  Roll Eyes

Go to almost any RV board & you'll see the "weight police" trying (often in vain) to point these issues out, but the boards are full of those who claim years of successfully ignoring the factory weight ratings. (In the Airstream club, there is a guy that insists his 1500 series suburban is more than adequate to pull his 34' Airstream. You should hear the excuses he makes for not being able to do more than 50 mph, or the busted tires, or the broken rear side windows (from chassis flex) . . . . )

Paint & polish sells & most RV dealers know most sit parked more than they are used . . . . The odds are in their favor to build them as cheap as they can. The consumers confirm this in their buying practices.

I had a friend that worked for freightliner custom chassis. The required service life of the axle affects the weight it is rated for. If the same axle was used in a FedEx truck & a motor home, the motor home would get a much higher weight rating because its service life is likely less than 10% of the fed ex truck (several million miles for the FedEx vs. only 100,000 miles for the motor home.)
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Sean
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« Reply #12 on: August 05, 2010, 11:14:27 AM »

...  Still only 800 lbs headroom between "as tested" and ultimate load capacity - that is only 5% or thereabouts. ...


Well, I admit that I have seen some RVing couples who might, umm, use up this margin just by taking their seats, but I think most will be pretty safe.  Still, as you say, it's not a lot of margin.  Your response caused me to surf over to FMCA to read the article (we're members, but gave up our magazine subscription years ago, when we hit the road).  To be fair, the test weight was with all tanks full, so other than a few personal items, it would be hard to put any more weight up front anyway.

By contrast, the rear is underloaded.  So the quickest way to get some relief up front would be to put a couple thousand pounds at the very tail, even if it's just ballast.  Our bus has just the opposite problem (well under axle limit in the front, and right at in on the drivers), and I found myself adding as much weight as I could in front of the steers to take some pressure off the drivers.

I think if I owned one of these, I'd try to go to a higher limit tire, though.  I'm certain the axle itself has more capacity.

-Sean
http://OurOdyssey.BlogSpot.com
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« Reply #13 on: August 06, 2010, 06:03:48 AM »

The last time I weighed with both of us aboard and full tanks, we were at 10,500lbs front and 20,500lbs rear.  The GVW (Gross Vehicle Weight) rating of the axles is 13,000lbs front, 23,000lbs rear.  Axle wise, we're 5,000lbs under!  I run Michelin 11R-24.5 XZE 16ply and they are rated at 14,320lbs front and 26,400lbs rear.  Tire wise that's 9,720lbs under tire capacity-so I only run 90psi in the tires for a very nice ride quality.  This is one of the many reasons of running a commercial bus.

Freightliner makes many motorhome chassis.  Even though this is one of the biggest, bigger are made.  Blame the motorhome manufacturers for not putting sufficiently stout chassis under their aluminum and plastic boxes.

My truck has 12,000lb front, 38,000lb rear tandem axles on 44,000lb 8 air bag suspension.  The current empty weight (I haven't put anything in yet) is right at 28,000lbs (the 32ft box weighs 10,000lbs).  On my bus, I added 3,000lbs for the conversion.  Even if I added 5,000lbs for the conversion and carry a 3,000lb car, that will put my weight at 36,000lbs.  Then if I pull a 10,000lb boat, that's 46,000lbs total-on a truck designed for 80,000lbs.  When I was trucking, the tractor and trailer weighed 46,000lbs empty!  And I remember pulling the southbound I-5 Grapevine at 50mph when empty.  I think the truck is just going to be loafing along-which is how I like it.  Good Luck, TomC
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