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Axle Weight Differences


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#1 bmccann

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Posted 04 August 2012 - 11:15 PM

This is my first time on the Forum.

I am an RV Newbie who recently bought my first Class A rig, a 2000 Holiday Rambler Endeavor DP. My problem is that I have an 800-900 pound difference in the weights of the front drivers side and passenger side wheels. I have tried to shift weight to the passenger side, but still have an 800 lb difference. This occurs with full or low fuel, and empty or 2/3 full fresh, Grey and black tanks.

My question is this- Is this weight difference abnormal, and if so, what can be done about it? Also, could this have anything to do with the suspension? The two slide outs are on the drivers side. The detail numbers on the weights are as follows: Front GAWR 10,400, actual weight 9700 (Left side 5250 Right Side 4450) Rear GAWR 17,000 Actual weight 16,500 (Left rear 8300-Right Rear 8200)

I have new Michelin XZA+3 on the front 275R/80 22.5 16PR LRH, and Toyo 295R/75 22.5 14 PR LRG on the rear, with a build date of 2007.

I am running with 95psi all around. Any thoughts or suggestions would be appreciated. Thanks

Bill
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#2 wolfe10

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Posted 05 August 2012 - 09:09 AM

Bill,

Welcome to the FMCA Forum.

Yes, different floorplans-- ones with much more "stuff" on one side can be substantially heavier on one side than the other.

And, yes, this can also be caused by suspension issues. Luckily these are fairly easy to check and adjust.

You will have three RIDE HEIGHT VALVES that control ride height. Two on one axle and one on the other. Check with your chassis maker for your "ride height specs". They are generally measured from a given point on the axle to a given point on the chassis.

IF you have safety stands and basic mechanical skills, you can check this yourself. But do NOT go under a motorhome, particularly to work on the suspension height without safety stands.

And, as you have already mentioned, you can move your personal gear around to put the heavier stuff on the lighter corner. Because most tanks are on center, they have little effect on left/right weight distribution.

Brett
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#3 bmccann

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Posted 05 August 2012 - 01:08 PM

Thanks, Brett.

I'm due for maintenance soon, so I'll have the ride height checked out.
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#4 wolfe10

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Posted 05 August 2012 - 03:48 PM

Bill,

Often there is a small amount of tolerance in the ride height specs-- as an example, 10" +/- 1/4". Sometimes you can "tweak" the ride height within the specs to better balance the weights. Check with your chassis maker.
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#5 bmccann

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Posted 05 August 2012 - 08:59 PM

Thanks Brett
I have a Freightliner chassis and the spec sheet I have only shows 6.80" as ride height with no +or - tolerance shown. I'll call Freightliner for the details.

Bill
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#6 rdtripn

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Posted 06 August 2012 - 04:02 PM

You stated in your post you are operating with all your Michelins at 95 PSI. Michelin tech help has told me to weigh my coach on all 4 corners with the coach loaded to travel and then contact them with those weights and they will tell me what to inflate the tires to. The specs on the vin placard should not be used. This appears to be quite a chore if there is no scales nearby to accomplish this and the weight numbers can be quite different such as whether you are traveling with full, gas tank water tank grey tank etc by numerous hundreds of pounds. Have read on several other sites about warranty issues due to improper inflation. Not an expert at this as we are in our first ever MH, 1999 Coachmen Sporstcoach 380MBS.
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#7 wolfe10

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Posted 06 August 2012 - 04:38 PM

rdtripn,

Welcome to the FMCA Forum.

Yes, BEST way to determine correct tire pressure is to weigh each wheel position. Take the heavier wheel position on each axle to go to your tire manufacturer's Inflation Tables. This will tell you the MINIMUM PSI for that weight. Most add 5 PSI to that minimum as long as it does not exceed the tire or rim max ratings.

And of course you have to factor in any tankage that you have that is not full as well as any personal gear or people who are not on board. As you know, the weight of any tankage/gear stored behind the rear axle will add more than it's weight to the rear axle than its actual weight and SUBTRACT weight from the front axle. Keep that in mind when weighting the front axle if the gas tank is well behind the rear axle and full.

Brett
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#8 Tireman9

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Posted 09 August 2012 - 08:36 PM

rdtripn,

Just to add a minor clarification on getting the RV weight. Some people try and cut it very close and think they need to weigh and adjust inflation every trip. It really isn't that imporatant as long as you are not overloading the tires or suspension. It is suggested that when you are ready to get the corner weights you have a full fuel & LP, the clothes and food you would pack for a long trip and have the water full. Also, all people and pets in their normal "travel" location. Now if you dump your holding tanks before leaving the campground then you don't have to worry about getting the weight with anything in the holding tanks.

Here is a link to a page that has general RV info and a very good worksheet on how to calculate corner weights. It covers just about every combination of Motorhome or truck & trailer.

Knowing the minimum inflation at your heaviest loading and setting all tires on the same axle to the same inflation based on the heavier side and adding the 5 psi Brett mentioned will mean that when you empty your fuel tank or eat all that food you will not be overloading the tires. Underloading in this case is OK.so you don't need to adjust the inflation down.

Remember check your air with a good gauge each morning before you travel and consider getting a Tire Pressure Monitor System that can warn you if you get a puncture and slow leak.
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#9 Carlonds

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Posted 03 January 2013 - 01:15 PM

Along the line of determining corner weights for our motorhomes, can any one provide recommendations for purchase of a small portable scale that can be used at home before we leave on the trip? I have a Roadtrek Class B, and single tires on the rear axle. I am interested in a small scale (probably 14" x 14") that would accommodate a single LT 245 Series tire? I have seen reference to these, but have no idea who might manufacture such an item...so am looking for some "seasoned" thoughts on this subject.
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#10 wolfe10

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Posted 03 January 2013 - 04:25 PM

Carlon,

I know that the scales used by RVSEF and many state truck enforcement divisions cost in the thousands of dollars-- just not practical.

Do you vary the weights between trips enough to warrant a reweigh? Most weight "when loaded as you travel" including full fuel and whatever level you normally carry in the other tanks. Use the heavier wheel position on each axle to access your tire manufacturer's inflation table for your tires. The table gives you the MINIMUM PSI for that load. Add a 5 PSI safety cushion to account for that "extra trip to Walmart" and you should be good to go.
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#11 jrwitt

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Posted 03 January 2013 - 05:47 PM

Here is a website for the ones (I think) that the RVSEFuses. It doesn't show prices, but you might be able to google it and find one. Or just call them. I am pretty sure Brett is right ... $1000s for a set. Let us know if you find something more reasonable.

http://www.loadometer.com/wl101.htm

Good luck!
Jack
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#12 werni8

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Posted 06 January 2013 - 11:23 AM

My spare Michelin is not an exact match to the Tokahoma. 22.5 but it's an 80, not 85 as rest of tires. I keep it in case I am somewhere, there is NO tire available. Florida Keys Etc. Will a mechanic put on an odd ball size tire to get me by?
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#13 Tireman9

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Posted 07 January 2013 - 12:07 PM

werni8


Can't speak for mechanic but if it were me I would say it depends.
If you are temporarily replacing a front I see no serious problem with the size mis-match.

However you should never mix size or brand or type in dual application. There are special matching dimensions to consider.

Also you should never consider limping home on a failed dual. You can temporarily take both fronts and move to one side in the rear. Then use the good tire that was a dual and place it and your spare on the front.

Now I am assuming you are making the change because you got a nail or such in one of the duals and you stopped because your TPMS warned you when you lost 20% or so of the minimum air needed based on the load. If you had an actual failure with serious loss of air on one dual you may have damaged its mate even with only a mile or so of travel and that tire should be considered as possibly damaged and not driven on until thoroughly inspected and pronounced OK by a rep from the manufacturing company.
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Retired Tire Design and Quality Engineer (40 years experience).
Retired Professional race car driver.
Retired Police Driving Instructor.
Member, FMCA Technical Advisory Committee
Delivered Tire Seminar for RV owners & two seminars on Genealogy at FMCA Bowling Green 2009, Madison 2011,

Indy 2012, and Perry & Redmond 2014

I hope to present two seminars on RV Tires & Three on Genealogy at Madison, WI  in August 2015

See my blog www.RVTireSafety.com and subscribe if you want notice of new posts.


#14 jfxg48

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Posted 11 January 2013 - 03:04 AM

bmccann and others.....

I have a weight disparity similar to the OP that I've been pondering for a while now. When I got corner weighed at the FMCA Eastern Rally last Oct in York I was actually quite pleased. The coach was 590lb under gross (30410/31000). Weighing was done with full fuel, propane; half-full fresh, gray, and black. Front axle was 250lb under (11750/12000), and the front tires were even within 30 lbs. Rear axle was 340lb under max (18660//19000) but my right rear dual was about 540lb heavier than the left (L9060 / R9600).

I aired up per Michelin's chart for the heavier side, and have had no problem for the ensuing 3000 miles as we made our way to Puget Sound for the winter. With the rear air balanced at the inflation for the heavier right side my left dual is running slightly underloaded, so that's OK. According to my tpms the pressures stayed balanced and the temps were all consistent and well below any problem areas. I had no handling problems, no drifting, no lean, no scary moments with trucks.

But I keep thinking about that. I don't think there's any way I could shift or compensate for that much weight, because a) there's no place on the left rear to store much, and I have about 400lb of battery and rack-2 engine and 6 house- mounted right there at the right rear. Some of that ought to have been balanced by the left-side bedroom slide mechanism, but apart from that the only left rear bays are the electric and water service bays. I've pretty much concluded that this is something I'll just have to live with.

Sooo...... What am I missing? Thanks.
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FX

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#15 wolfe10

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Posted 11 January 2013 - 09:00 AM

John,

While it would be ideal to get side to side weights closer, you are within industry standards.

Other than moving some of those batteries, I would suggest that you check your ride height. Check with your chassis manufacturer for the ride height specs AND for tolerances (plus or minus difference). If the ride height on the light side is lower than spec/heavy side is higher than spec, a mere adjustment will help some. Also, some give 1/8" tolerance which can be used to fine-tune side to side weights (raising ride height on a side increases the weight it carries. Do NOT go outside of your chassis manufacturer's specs.
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#16 jfxg48

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Posted 14 January 2013 - 03:25 AM

Thanks, Brett!
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FX

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#17 Allegiance40x

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Posted 17 January 2013 - 04:54 PM

My Spartan manual says "If the weight of one side of an axle exceeds the weight on the other side of that same axle by more than 5% of the total axle rating (GAWR), it is necessary to redistribute the load appropriately."
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