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Old 12-12-2013, 05:41 PM   #15
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Originally Posted by jimbo2013 View Post
Well as of now before I did the scale weights I have 95 in the fronts and 100 in the rears. The engine was running all the time on the scales, so full air pressure It drove ok on my first 120 mile trip, so can the tires be that far off? In looking at the coach on flat pavement it sits very level to the eye, the tires don't appear squat on one side vs the other. With the variation I stated above wouldn't you think I would see a difference? All confusing, I can do a reweigh it's only $12, but don't understand why dumping the air would matter, by I can try it.
In my experience, when dealing with psi up around 100, you won't be able to see the weight variance in the sidewall deflection. The reason I was given for dumping and refilling the air bags is to allow the ride height valves to reset with the coach in a fairly level with wheels straight attitude. The ride height valves don't respond particularly well in slow parking lot turns and maneuvering. If you re weigh, please repost & let us know if this results in any significant difference.
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Old 12-12-2013, 06:47 PM   #16
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Steve, that diagonal imbalance doesn't look at all right to me either. I'm really struggling to come up with a way that front end could possibly be 1100lbs heavier on one side? That and the fact the opposite corner is also heavy says to me there's a good chance something is going on with the ride height valves - or possibly with the method/equipment used to get the weights.
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Old 12-12-2013, 07:37 PM   #17
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DG, thanks for your very excellent comments. I was amazing the variety of reactions I received from my 50 lb and disaster comment. Now, I will be very serious. I have had a very active career in a technical field and have a very practical view of mechanical things.

There are so many variations in something as complex as a motor home. We buy RVs to use and enjoy. Relative to the weight issue, the axles and are designed for an operational weight which is posted on your info sheet as the axle weight rating. The tire manufacturer also give you a weight rating for the tires as a function of the internal pressure. The maximum here is the weight published at the maximum pressure in the chart. Weight you unit loaded from travel front and back and select the psi for the maximum weight of the two front tires and similarly the maximum for the rear tires. Add 10% to each and round off to the next higher number ending in either 0 or 5 and that becomes you fill pressures, one for the front and one for the rear. Check the appearance of the unit loaded for travel on a level surface to make sure level and everything else look right. Stop worrying and enjoy your unit.

The ten percent is added to account for all of the variations. Rounding off is to account for how you will be using your unit. The water for example will weight 800 pounds and most of it can be shifted from tank to tank and you can possibly get 800 more pounds in the waste tanks. And we often will haul heavy stuff home and one really can not stop and reweigh. Also remember that modern tires are wonderful devices and can be operated for periods of time well over their load rating. For example, there are some people who neglect their equipment and it has often amazed me that they do not appear to have excessive tire problems.

The air suspensions on the larger RVs are also wonderful devices. They seldom need service and the account for almost all variations in load distribution and still ride level and provides an excellent ride. Do not over manage and let this device work for you.
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Old 12-12-2013, 08:38 PM   #18
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DG, thanks for your very excellent comments. I was amazing the variety of reactions I received from my 50 lb and disaster comment. Now, I will be very serious. I have had a very active career in a technical field and have a very practical view of mechanical things. There are so many variations in something as complex as a motor home. We buy RVs to use and enjoy. Relative to the weight issue, the axles and are designed for an operational weight which is posted on your info sheet as the axle weight rating. The tire manufacturer also give you a weight rating for the tires as a function of the internal pressure. The maximum here is the weight published at the maximum pressure in the chart. Weight you unit loaded from travel front and back and select the psi for the maximum weight of the two front tires and similarly the maximum for the rear tires. Add 10% to each and round off to the next higher number ending in either 0 or 5 and that becomes you fill pressures, one for the front and one for the rear. Check the appearance of the unit loaded for travel on a level surface to make sure level and everything else look right. Stop worrying and enjoy your unit. The ten percent is added to account for all of the variations. Rounding off is to account for how you will be using your unit. The water for example will weight 800 pounds and most of it can be shifted from tank to tank and you can possibly get 800 more pounds in the waste tanks. And we often will haul heavy stuff home and one really can not stop and reweigh. Also remember that modern tires are wonderful devices and can be operated for periods of time well over their load rating. For example, there are some people who neglect their equipment and it has often amazed me that they do not appear to have excessive tire problems. The air suspensions on the larger RVs are also wonderful devices. They seldom need service and the account for almost all variations in load distribution and still ride level and provides an excellent ride. Do not over manage and let this device work for you.
Excellent points sir.
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Old 12-12-2013, 08:42 PM   #19
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I'm going to call FL tomorrow and get the ride heights for my chassis, take a quick measurement.

I agree the diagonal difference is puzzling.

When I'm sure the ride height is correct I'll re weight dumping the air as you suggest Steve.

tks for the input
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Old 12-13-2013, 12:48 PM   #20
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Dumping the air is an extreme example of over managing. You put a scale between each wheel and the ground and take a reading. It absolutely makes no difference what you do with the air in the suspension system. Besides are you going to travel without air in the suspensions. Simply amazing how some non technical people can chase their tail on issues they have no comprehension.
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Old 12-13-2013, 01:04 PM   #21
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Dumping the air is an extreme example of over managing. You put a scale between each wheel and the ground and take a reading. It absolutely makes no difference what you do with the air in the suspension system. Besides are you going to travel without air in the suspensions. Simply amazing how some non technical people can chase their tail on issues they have no comprehension.
Targaboat, you are certainly free to ignore any suggestion made by me and to delete my posts with reckless abandon. I assure anyone else that it has merit and this will be my last post on this subject.
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Old 12-13-2013, 02:36 PM   #22
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My question is "Why all the fuss about having tire pressure exact ALL the time"???? I drove truck over the road for 20+ years and NEVER put a tire gage to the tires, and bet the shop checked pressure only every 3 months when truck was in on a service, and in 20+ years had ONLY 1 recap drive tire have the cap let loose, and 1 steer tire blow (I ran over a piece of metal).

ps. forgot to add, this was a total of over 1 million miles too.
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Old 12-13-2013, 02:51 PM   #23
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Was it YOUR truck?
We're you paying to replace tires that wore out faster than they should have?
Were the tires surrounded by very expensive fiberglass?
If you lost a tire was there a possibility it would cause harm to a member of your family?
If a tire blew, did it ruin your vacation?
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Old 12-13-2013, 08:13 PM   #24
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Dumping the air is an extreme example of over managing. You put a scale between each wheel and the ground and take a reading. It absolutely makes no difference what you do with the air in the suspension system. Besides are you going to travel without air in the suspensions. Simply amazing how some non technical people can chase their tail on issues they have no comprehension.
With the info supplied by the OP, it would seem like somebody with a high degree of "technical ability" might be considering the potential for one leg of a 4 legged stool being a little long (one of 4 airbags overinflated, or one corner of a more sophisticated system)?

No matter how you troubleshoot that potential, I think it merits some attention. Steve's plan for duplicating the OP's weighing process, without air in the air bags, might not be my plan, but it should work, eliminating the potential for one overinflated bag/corner to be causing the problem? For a clever person, it should be easy to see his thoughts about deflating the bags had nothing to do with going down the road that way....
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Old 12-13-2013, 08:27 PM   #25
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An overinflated air bag will raise the coach higher at that corner, but makes no difference on the weight pushing down on the tire. I don't think the air ride height will cause any major weight differences unless all the liquids shift to one side. The 120 psi tire pressure is a bit much, but again shouldn't affect weight.
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Old 12-13-2013, 10:12 PM   #26
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So much misconception in these posts. if you want to understand this stuff in detail, there are several good references such as Carroll Smith's "Tune to Win".

First of all, an airbag is a spring, and the pressure within determines the ride height AND the spring rate, because the only way to raise a fixed weight (with a linear suspension system) is to apply more rate. The ride height adjuster is a pressure relief valve.

The pressure in a tire for a given weight is designed to create a specific contact patch area for optimum wear and handling.

If your coach has a left-right weight bias it's most likely to be the result of the basic design elements and how you pack it. Pressure in the tires at the time you weigh it has some effect, but it's miniscule compared to the effects of the basic structure and the pressure in the bags. If you really want to understand the design effects, weigh it once fully loaded with full tanks and again empty and see what changes.

There are some peculairities of solid front axles that come in to play, It's actually easier to do this with an IFS but the same basic principals apply. Generally speaking, if you want the coach to track straight (on a flat surface), you would start by checking ride heights to ensure the fronts are equal and the rears are equal. Then weigh and look at the differences. What you really want is for the front weights to be as equal as possible. Given that most of us worry about overloading the fronts, You would take the HEAVY side of the front and REDUCE the ride height on the OPPOSITE rear corner until the front weights are equal. The rears will be what they will be, it doesn't matter, as long as you don't overload the tires.

Then you align the fronts. Of course, road crown will then produce a pull, and this has to be compensated.

As far as pressures go, they should be set for the weight on each tire to create a consistent patch. If that means four different pressures, that's the way it goes. If you want to make it easy, use the higher pressure on each end so you only have two, not the lower.

The loaded vs unloaded will tell you a LOT, but again, you have to have the ride heights correct first or it doesn't mean much.
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Old 12-14-2013, 04:55 AM   #27
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Yawn!
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Old 12-14-2013, 10:10 AM   #28
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My last diesel MH had springs along with supplemental air springs. That would easily justify the readings the OP made. I like the post that suggests that one needs to understand the whole system.

Now, time for my nap, have fun.
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