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Old 12-14-2013, 08:13 AM   #1
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Wandering, weight distribution

I wanted to post my findings about wandering and tracking. My fresh water tank is just in back of the rear axle. The grey and black water tanks sit just in front of rear axle.
I started off a trip last week with a full fresh tank (100 gal) about 800 lbs. Traveling to friends and family I did not have reason to add water or the opportunity to dump.

At the end of the week the tracking and handling are very, very much improved!!! The fresh water tank is close to empty and that weight has been shifted forward to the grey and black tanks. Net shift of about 1600 lbs. Absolutely amazing! At the start of the week, I was wandering all over the place. By the end I could release the wheel and it track straight and true!!!

My observation is that if I know I will have water available where I'm headed that I will only fill 1/4 full fresh and may add as much as 1/4 - 1/2 to the grey tank.
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Old 12-14-2013, 08:58 AM   #2
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Weight shift can cause all kind of good or bad behavior. With that kind of weight change I'd suggest you evaluate your tire pressures. 1600 lbs more or less should require an pressure adjustment. safe travels.. ed
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Old 12-14-2013, 09:09 AM   #3
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In this case the weight difference on the tires is 800 lbs, not 1600, and that weight was added when the tank was filled. Shifting 800 lbs from one side of the rear axle to the other did not change the tire load - the rear axle tires are carrying nearly all that water weight whether in the fresh tank or the gray.

But adding 800 lbs to any axle is a large enough change to make a tire pressure check wise. What you need to check is not so much the tire itself as the psi vs the tire's load inflation table, to make sure the pressure you are carrying is sufficient for the increased weight. If the tank was empty when you weighed it, then you may not have set the original pressure high enough for the much heavier weight when water is added.
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Old 12-14-2013, 09:42 AM   #4
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The main reason for the better handling was shifting the weight from behind the axle to in front. When the weight was behind the axle it was a case of "The Tail Wagging The Dog" in other words the weight behind the axle cause addition rear sway. Once the weight was in front of the axle no more rear sway.
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Old 12-15-2013, 02:37 PM   #5
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Quote:
Originally Posted by D Lindy View Post
The main reason for the better handling was shifting the weight from behind the axle to in front. When the weight was behind the axle it was a case of "The Tail Wagging The Dog" in other words the weight behind the axle cause addition rear sway. Once the weight was in front of the axle no more rear sway.

I would agree with this theory except that the OP has a heavy diesel engine sitting further behind the axle and the weight of the water going from "just behind the rear axle to "just" in front of the axle would have little effect on the stability of the coach. I would be more interested in knowing the fuel weight on the front tires along with what tire pressures he is running. You might be correct if it was a gas engine and the fresh water tank was a higher percentage of the rear overhang weight, but in this case, I think a shift of 7-800# over the axle wouldn't be enough of a weight shift to affect handling.
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Old 12-16-2013, 06:04 AM   #6
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Fuel at best handling was a little above 1/2, on a 90 gallon tank. I dumped the grey water for the final leg of the trip and still had about 1/4 left in the fresh tank. After a fill up handling was a little better.

The handling was okay but not as good as when I had a good load in the grey tank.

Tires are all at 100.
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Old 12-16-2013, 06:19 AM   #7
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I start out all trips with zero grey/black and full H2O. The difference is in my case I believe all tanks are forward of the duals/tag. moving water from one to the other makes little difference in handling. Perhaps this is due to the tag axle providing for better weight distribution and a smoother ride. The changes when diesel is full versus at 1/4 are also not noticeable. I always try to refuel between 1/4 and 1/2.

I guess the heavier/longer the coach, the less these type of changes make in overall handling.

As more weight is put behind the duals as is your case when the H2O tank is full, that lifts a little weight off the front axle. When weight is removed from the front axle, the steering will be slightly affected, causing the wandering handling your describe. If the weight distribution is close to marginal, these minor shifts could make significant differences. I would suggest that perhaps moving some of your heavier "stuff" you carry further forward may help with the wandering handling problem.
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Old 12-16-2013, 10:14 AM   #8
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Yes, the shift of weight from behind to in front of the rear axle has an effect on the steer axle. I just went through several six position weighs to take some weight off the steer and add more to the drive. When I started, the steering axle had more weight on it than the drive axle. I did this by replacing the proportioning valves with manual regulators which allowed me to determine how much weight I wanted the tag axle to carry. What I learned was that for every 6# I took off the tag, the steering axle reduced by 1#. In my case, I reduced the tag weight by 4000#s which took 660#s off the steer axle. All of the 4660#s went onto the drive axle where it was needed. The OP's MH does not have a tag axle, but the weight transfer effect would be the same. Taking 800# of water away from behind the axle would add about 130#s to the steering, an transferring that 800#s forward would add another 50-70#s to the steer. I don't know if 200#s more on the steering axle could make a handling difference, but it must according to him. There are a lot of factors that contribute to the good or bad handling of a big box on wheels. Sometimes it takes awhile to find the right combination.
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Old 12-17-2013, 06:50 AM   #9
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Smile Weight shift.

I don't have much stored behind the rear axle. Access to the engine batteries, and AC power bay take up most of the storage, space. Tools only take up about 40 lbs. The water is the most significant weight.

I have read many posts and replies about wandering, most if not all focus on tire pressures, sway bars, etc. The water weight change was so dramatic, i felt it pertinent to share.

I will probably preload my grey tank for longer trips or where I need to carry fresh water. It easy to dump clean grey water just about anywhere I go.
Thanks All!
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Old 12-17-2013, 09:19 AM   #10
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I have often wondered what the ratio of front axle to rear axle weight should be for optimal handling. I wonder if there's actually any data for this, or has it always been done by guess or by golly?

It seems odd that the water tank would be placed behind the rear axle. There's already a lot of weight back there.

Jim
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