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Old 06-21-2014, 11:30 AM   #57
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Originally Posted by Gordon Dewald View Post
Most of this is due in part to having more information closer at hand.

In the old days you bought a vehicle and perhaps you put overloads on it and pumped the tires up to carry a larger load. I recall Dad putting side boards on the 1/2 ton truck to take a load of grain into town. The tires looked "squashed" but we drove the 15 miles at 30 mph and always got there safe. Back home he took the sideboards off and let some air out of the tires.

Now days we have much more complex systems able to take higher loads at higher speeds. Part of the issue is the new systems come with adjustments. This is part of the technology improvements developed by folks who thought they would make things that could be could be customized for unique situations. Not only engineers but practical people who see a need and tinker until they come up with a good solution.

We are the beneficiaries of those custom adjustments. You do not have to make the adjustments unless things are really out of whack - and even then you have to be aware that something is not as it should be. A lot of us with no experience have nothing to use as a base line so accept whatever we have until we talk to someone who says "Mine does not do that".

IMO the example of a rear axle being 2700 lbs heavier on one side than the other makes me think something is not right. I expect the MH manufacturer did not design or build the MH with a weight difference that large. I could find no information on the net to confirm that but that is about 10% of the coach weight.

Bottom line - if the coach handles the way you expect and the tires are wearing evenly is there anything to worry about?

Just saying!
Most manufacturers design floor plans that will sell. I'm sure they do consider where the weights are going to be, but a floor plan design takes precedent over balance. They also want the most storage underneath that is possible. When completed, they know that eye appeal, convenience an comfort are going to sell the coach. The fact that it might be heavy on one area and light on another doesn't bother them as long as they do not exceed an axle or tire rating. A lot of MH's travel with the tires at maximum psi and 1500-3000#s heavier in one side or the other. A lot of people are ok with that or just don't know it and may never have a problem.
So to answer your question, probably not. I spent a lot of time getting our coach balanced and the tires properly inflated. In the end it might be more for my peace of mind than any lasting benefit to the coach. It handled just fine when we bought it, but my insistence on getting it better discovered an imbalance that was loading a front tire above it's max rating. That might have lead to a front tire blowout, but maybe not. I just have more confidence now when we hit the road that I have done what I can to insure a safe trip.
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Old 06-21-2014, 12:34 PM   #58
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How funny...5 pages of posts and not one comment about the fact that 3 different air pressure gauges will likely give you 3 different readings. While so many are completely anal about 5 pounds one way or the other, their gauge could actually be wrong.

Perhaps in the reading of manufactures "recommendations" it was overlooked that most will give you a minimum pressure as well as a maximum pressure. The engineers tell me that anywhere between those numbers is safe for max load. On our fleet I had the drivers lower trailer tire pressure to 85 psi and our tire failure rate seems to be going down...or perhaps we are just in a lucky streak.
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Old 06-21-2014, 12:48 PM   #59
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Originally Posted by 336muffin View Post
I know I will be burnt for this but..............when a tracter and trailer rig cross' s the US with 10,000 pounds and then comes back with 48,000 pounds do they adjust tire pressures? No. I'm just giving something to compare.
You are correct but trucking companies have other concerns that take priority over driver comfort.

- They try and run loaded as much of the time as possible
- They don't want to spend the 1/2 hour to let the tires down $$
- They don't want to spend the 1/2 hower to re-inflate $$
- Can't be sure they have access to 100+psi air when away from "home"
- Don't forget the air suspension under the cab and under the driver seat which means the driver feels less discomfort than you would
- Trucks not carrying dishes, and other household goods which could break from harsh ride.
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Old 06-21-2014, 12:51 PM   #60
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One sure has to wonder why all tire makers publish a load chart telling people the recommended pressures for a given load. Could it be that through research and testing they have determined what pressure will give the best tire life, ride and handling characteristics? That would also result in the safest pressure. I guess I will go with what the tire maker thinks is best.
Don't forget most people wear the tires out so they want max tire wear. RVs on the other hand usually "age out" so wear is less of a concern than good ride.
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Old 06-21-2014, 01:14 PM   #61
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so if the weight of your front left corner requires you to run at 60 pounds and the weight on the right front corner requires you to run 90 pounds, how do you think that rigs is going to steer ? Would you weight police out there do it ? Now I suppose the air pressure difference in the back tires wouldn't make as much difference as the front tires would in the steering input.
We are talking Motorhomes here and not trailers, pick-ups or cars.

All street vehicles should run the same pressure for all the tires on any single axle. The inflation for tires on a single axle should be based on NO LESS than what is needed to carry the load on the heaviest loaded tire.

Handling response should be the same when turning Right as when turning Left and you get the most uniform handling when both fronts have the same inflation.
In the rears it would be braking response that would most likely be un-balanced if you

RE your example of 60 psi vs 90. Most 22.5 dia tires stop at 65 psi and you should not run at a pressure that is not on a chart. but comparing 65 with 95 I note this would mean a side to side unbalance of over 1500# which to me indicates some other significant problem that needs correcting.
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Old 06-21-2014, 01:15 PM   #62
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Wouldn't this theoretically mean you're over inflating one tire which would lead to crowning tire wear and rougher ride, which is the reasoning for doing the four corner weigh to eliminate?

Yes in theory but hopefully your RV is balanced to a more reasonable level so the 5 psi difference is not significant on were rates.
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Old 06-21-2014, 01:19 PM   #63
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FWIW, tire technology has changed over the years. My Dad relayed to me when he was a young 1000 miles on gravel road was all you could expect from a tire, today if I don't get 70k I feel like I'v chosen poorly. Goodyear Marathons, when I was running them, per factory guidance said to inflate them 10psi over the sidewall max for continuos speeds above 65mph.

I've found over the years that old trucker wisdom has value. Back in the day of gasoline truck engines the valves would float before the motor would be hurt, so to get max performance without the benefit of a tach, turn on the windshield wipers and shift when they stopped.

That all said, I use the tables to set tire pressure. My engineering background makes me a firm believer in the science. There are a few safety concerns with inflating to max sidewall pressure. My concern is where does the tire perform best? Max pressure may hydroplane sooner. Max pressure will have a smaller tire patch to brake and turn with. When not loaded to max weight. How much difference? Enough to make a difference? Maybe.
Multi-axle trailers are not in the same boat as Motorhomes, pickups or cars that have tires "at the corners"

Due to structural forces unique to trailers they should inflate to the tire sidewall max. Most trailer placards specify the tire sidewall max.
HERE is the technical reason Trailers are different.
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Old 06-21-2014, 01:30 PM   #64
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Here are a couple of POSTS on the topic of weighing. Actual numbers are used.
Hope these help clarify.
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Old 06-21-2014, 02:26 PM   #65
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Most manufacturers design floor plans that will sell. I'm sure they do consider where the weights are going to be, but a floor plan design takes precedent over balance. They also want the most storage underneath that is possible. When completed, they know that eye appeal, convenience an comfort are going to sell the coach. The fact that it might be heavy on one area and light on another doesn't bother them as long as they do not exceed an axle or tire rating. A lot of MH's travel with the tires at maximum psi and 1500-3000#s heavier in one side or the other. A lot of people are ok with that or just don't know it and may never have a problem.
So to answer your question, probably not. I spent a lot of time getting our coach balanced and the tires properly inflated. In the end it might be more for my peace of mind than any lasting benefit to the coach. It handled just fine when we bought it, but my insistence on getting it better discovered an imbalance that was loading a front tire above it's max rating. That might have lead to a front tire blowout, but maybe not. I just have more confidence now when we hit the road that I have done what I can to insure a safe trip.
I agree with the design and selling aspects of creating a MH.

However to design and build a 30000 lb motorhome with a 2700 lb difference on one axle is illogical. That would be like offsetting the engine to one side, putting in 27 - 100 lb batteries or 270 gallons of water on that corner. Totally possible but not likely.

I did some calculations based on a 38' Forza with a GVWR of 27910 and rear axle GAWR or 17,500. To have a 2700 lb difference would mean one side of the rear axle would have 7400 and the other 10,100. The heavy side would be carrying 36% of the weight of the coach at max weight.

The designers may have a lot of input but I believe the design will go through an engineering analysis. In most of the cases such as yours it was a mechanical issue that caused the problem.

I am similar to you in that I like to optimize stuff. It may take some effort to do so. I like to think things through and apply logic to the problem. Then I decide whether the benefit cost is worth fixing the problem. Most of the time if it is not too costly I like things to be 'right'.
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Old 06-21-2014, 03:57 PM   #66
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HERE is the technical reason Trailers are different.
Here is the document for the trailer tire inflation I mentioned.

Here is real sidewall deflection.
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Old 06-22-2014, 07:03 AM   #67
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I agree completely with your post about changing technologies enabling us to do so much more than just our fathers ever could. We are supposed to get smarter as we get older. Lord knows in my case that's a pretty low threshold for a challenge. But I now feel a responsibility to do what I can to safeguard my passenger(s) and those on the road around me, and do the homework necessary to take advantage of that technology in a safe manner. Few enjoy homework, but the attitude by some that we can operate a motorhome while blissfully ignorant is a scary thought. We are responsible--period.
You also wrote: "IMO the example of a rear axle being 2700 lbs heavier on one side than the other makes me think something is not right. I expect the MH manufacturer did not design or build the MH with a weight difference that large. I could find no information on the net to confirm that but that is about 10% of the coach weight." That is our coach and my challenge is for you to come to my house and reload any and everything we have put into our coach to redistribute the weight properly. We have 50 amps and water available in case it takes you more than one day. I will even buy you any dinner in town if you can get the rear axle weight difference below 500 lbs. I suspect you will find (as did we) that the MCC pillow arrangers held sway over their engineers and the layout in the basement precludes any significant weight redistribution. It is an excellent example of just what we write about with changing technologies above. Somebody needs to be in control who knows what he/she is doing. Fortunately, there are safe workarounds for our weight issue, and I believe we have made things not only safe, but now comfortable--we changed lots of things I have not mentioned. But it took doing homework and asking questions and yes, money. We are ultimately responsible for operating a safe vehicle. Once we are in a court of law, its a bit late to be thinking about what we should have done. But at this stage in life most important to me is my conscience and how I would feel if I caused injury or worse to another when I could have prevented it had I not been too busy to do my homework.
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Old 06-22-2014, 07:58 AM   #68
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Good for you and your discovery of an overloaded front tire. That is doing your homework.
Our Cayman is the coach with a 2700 lb heavier passenger rear side. I wonder how many of those who choose to believe the problem is my 'stuff' loaded improperly and not MCC 'pillow arrangers' decisions that were never vetoed by staff engineers have ever had a four corner weighing done on their own coaches? Ignorance is not bliss. I have read that Monaco Coach Corporation (MCC) did not have an engineer on staff. The important thing is to find out and fix it, as you have done.
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Old 06-22-2014, 06:44 PM   #69
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How funny...5 pages of posts and not one comment about the fact that 3 different air pressure gauges will likely give you 3 different readings. While so many are completely anal about 5 pounds one way or the other, their gauge could actually be wrong.

Perhaps in the reading of manufactures "recommendations" it was overlooked that most will give you a minimum pressure as well as a maximum pressure. The engineers tell me that anywhere between those numbers is safe for max load. On our fleet I had the drivers lower trailer tire pressure to 85 psi and our tire failure rate seems to be going down...or perhaps we are just in a lucky streak.
I have tested a number of gauges at various rallys and conventions. Did some blog posts with some of the results. Here is one post showing a 36% failure rate. Normally I only find 10 to 15% fail. So yes gauge accuracy is important. I even offered some information on how to confirm the accuracy of your own measurements.
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Old 06-22-2014, 06:50 PM   #70
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Here is the document for the trailer tire inflation I mentioned.

Here is real sidewall deflection.
Yes I am aware of the Goodyear only tech bulletin that TireRack publishes. I believe Towmax has similar but not identical bulletin

People should never use a Tech bulletin from one company to justify load or inflation or speed or usage for tires from a different manufacturer, just as you would not use a GM spec oil filter on a Ford engine.
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