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Old 04-19-2016, 11:42 PM   #1
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Tag Axle Loading with Hydralift and Harley

I've seen older, related threads but my questions are a bit different.
I've learned a lot about how loading affects axle weight and wheel alignment. But what is the party line on how to deal with a M/H that may at any time have a 1200 pound difference in loading?

Specifics: 2008 Fleetwood Revolution LE 42, Spartan chassis, 44,600 GVWR, with a Tag Axle. I have a hydralift that I carry a 900 lb Harley Ultra motorcycle.

I run about 50% of the time with, and 50% of the time without the harley. When I drive with the Harley the front end is a bit light and it's affected the wear on the front tires quite a bit. I've been reading about adjusting air bag loading to balance out the loading between front, drive, and tag axles. But if I adjust the loads with the harley on board, it would make the front axle really heavy when we leave the Harley home.
What is the thought or recommendation on how to account for the significantly different loading scenarios?

I haven't weighed all the axles yet, so could use some advice on how to do that when the local scale is a single platform scale.
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Old 04-20-2016, 12:07 AM   #2
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Weigh at a CAT scale, available at most truck stops. $10.50, they have three pads so you can get weights for each axle. https://catscale.com/how-to-weigh/ Weigh it 2x, both with and without the Harley. A second weighing(reweigh) is $1 more. When they ask for a number, just tell them you are a private motorhome.

Most newer tag axle coaches are heavy/overweight on the front axle, with as much as 10,000# excess capacity on the tag/drive axles. It's critical you have all three axle weights(with the coach loaded for traveling and full tanks) so you can make an informed decision about the need for tag adjustment.

Not familiar with Spartan system, but my Powerglide coach is now modified so I have manual proportioning valves with easy access for tag/drive pressure(weight)adjustment. This mod was done in order to reduce weight on the front axle, which was over factory rating, not because of a Harley on the rear issue. From the factory owner accessibility/adjustment to the valves was not possible.

Reducing weight(pressure) on the tag will also reduce weight on the steer axle, approx. 6:1 ratio... reducing the tag 600# will therefore reduce the steer 100#. All of that 700# reduction will be added to the drive axle.

Your Hydrolift is permanently mounted(fixed weight), and the 900# Harley is the variable. That center of gravity is maybe 12' behind the drive axle(the fulcrum). Your coach wheelbase is around 24-25'. My physics is pretty rusty but, using a 1:2 ratio, adding a 900# Harley would reduce the steer axle weight by 450#. I don't think a variable 450# reduction on the steer axle is a concern.

Someone on the TRVN forum with an Allegro Bus towing a very heavy box trailer(think tongue weight) did the modification so he could adjust the tag for driving with/without the trailer.

My guess is that you have so much extra capacity on the rear that it won't matter whether you adjust or not. Also I'd guess that abnormal wear on the front tires is more likely due to alignment than the Harley. Maybe a good alignment shop can give their assessment of your tire wear. My 2˘. I'll be interested to read comments of those who do hang a Harley on the back.
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Old 04-20-2016, 12:14 AM   #3
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Quote:
Originally Posted by TurtleKent View Post
Most newer tag axle coaches are heavy/overweight on the front axle, so it's critical you have all three axle weights(with the coach loaded for traveling and full tanks) so you can make an informed decision about the need for tag adjustment.
I guess ours is an exception then as we are 1,970#'s under the tire/axle rating on the front when loaded and us in the seats.
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Old 04-20-2016, 12:46 AM   #4
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NTG58,
Its common to adjust the drop axle load on dump trucks with an air pressure adjusting regulator. This regulator is basically the same you would find on your home shop air compressor.

This system is not found commonly on RV/motorhomes with a tag axle because on our tag axles, we have a height control valve that varies the air pressure on the tag axle while it's in use based on height, and is set to only provide a predetermined and lower percentage of load carrying capacity split between the tag and the drive axle.

In order to have driver seat adjustable system, you would need to delete the auto height valve and use a hand operated pressure regulator like in the dump truck.

But, this would not be a good option on tag axle applications as changing the load carrying ratio (taking too much load off the drive axle), would cause tire wear issue on the drive axle, and decease your tight turning capability.

Another problem that you would face is you would need to pay more attention to the operation of your suspension system and not allow your tag axle to over extend and damage your air springs and possibly your shocks.

The over extension issue can be controlled by adding limiting straps, another added expense if the shocks are not controlling it.

Basically, with out going into a re-engineering exercise, your only option is adjusting your tag and drive axle tire pressures to the heavy side of the load chart when you carry your bike.

Be sure to have good shocks up front to control your rebound properly. That has a lot to do with your feeling too light up front when you have your bike on back.

Storage compartment loading is also something under your control, and in your favor.

Hope that info helps

DTW
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Old 04-20-2016, 12:57 AM   #5
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Quote:
Originally Posted by Mr_D View Post
I guess ours is an exception then as we are 1,970#'s under the tire/axle rating on the front when loaded and us in the seats.
Mr D, maybe it's your big ISX with all those Lbs Ft of torque in the rear. What is your front axle rating?

Seriously tho, I know the tag axle Allegro Bus is close to max rating on the steer axle(even my 2010), and the tag axle Dutch Stars had serious overweight problems this year. A couple of long threads ran on the Dutch Star problems. I've read speculation it's the bloat from full wall slides and all the marble, mirrors and doodads contributing to the weight gain.

It all comes down to getting accurate axle weights in order make informed decisions. Safe travels.
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Old 04-20-2016, 01:17 AM   #6
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Mr D, maybe it's your big ISX with all those Lbs Ft of torque in the rear. What is your front axle rating?

Seriously tho, I know the tag axle Allegro Bus is close to max rating on the steer axle(even my 2010), and the tag axle Dutch Stars had serious overweight problems this year. A couple of long threads ran on the Dutch Star problems. I've read speculation it's the bloat from full wall slides and all the marble, mirrors and doodads contributing to the weight gain.

It all comes down to getting accurate axle weights in order make informed decisions. Safe travels.
Front axle is 20,000, drive is 20,000 and tag is 14,000.

And yes, Newmar had to step up and replace the front axle on our '02 Dutch Star due to it being overweight at delivery. Went from a 12,000# to a 14,600# axle.
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Old 04-20-2016, 01:23 PM   #7
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Awesome feedback from all of you, I do appreciate it.
Based on that, my new plan is....
Take to a CAT scale, weigh all three axles both with and without the bike.
And if I can get all three axles within specs on both scenarios- then I'm golden, from a weight perspective.
Then yes, I know I need a full three axle alignment to help correct some of my tire wear issues. And then I'll just have to watch the tire wear and see how it goes.
My concerns really started when I could see the tire wear, and I could physically measure the change in coach height at the front wheels, and could physically measure a change in chamber on the front wheels, both with and without the bike loaded.
I think you guys have given me enough to get coach into a nice middle ground (I think I'll pass on any thoughts of installing an adjustable air system).
It will take a couple weeks to get this all done, but I'll let you know how it works out.
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Old 04-20-2016, 01:35 PM   #8
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Since your chassis manufacturer does'nt allow user adjustment of tag axle loading ( my Roadmaster chassis does ), all you can do is get 3 axle weights, with / without bike, and adjust tire pressures acordingly.

I also have a hydra-lift !!
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Old 04-20-2016, 05:56 PM   #9
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Quote:
Originally Posted by NTG58 View Post
I've seen older, related threads but my questions are a bit different.
I've learned a lot about how loading affects axle weight and wheel alignment. But what is the party line on how to deal with a M/H that may at any time have a 1200 pound difference in loading?

Specifics: 2008 Fleetwood Revolution LE 42, Spartan chassis, 44,600 GVWR, with a Tag Axle. I have a hydralift that I carry a 900 lb Harley Ultra motorcycle.

I run about 50% of the time with, and 50% of the time without the harley. When I drive with the Harley the front end is a bit light and it's affected the wear on the front tires quite a bit. I've been reading about adjusting air bag loading to balance out the loading between front, drive, and tag axles. But if I adjust the loads with the harley on board, it would make the front axle really heavy when we leave the Harley home.
What is the thought or recommendation on how to account for the significantly different loading scenarios?

I haven't weighed all the axles yet, so could use some advice on how to do that when the local scale is a single platform scale.

Well Sir,
I guess I'm a bit wondering here. I've done all that you're presently doing and, it was on our present rig, an '04 Itasca Horizon 36GD with the C-7 330HP CAT. I did all the install and setup for that Hydralift and all that's related. I carried an '08 Honda GL1800 Goldwing. It hovers very close to 900 lbs. and, I was warned about "excessive" front end un-loading when I was about to embark on the install.

Well, I weighed my coach, front end, rear and total. When it was all said and done, my front end was right at 198 lbs. less than it was without the Hydralift and the Wing. I could remove that much by simply getting out of the passenger seat and walking to the rear while the wife was driving. So, that kind of weight transfer was not even considered to be any sort of issue.

As far as the ride height on your coach. Well, not sure how yours works but, on ours, the ride height was the EXACT same with the bike on there, as it was without it. The ride height sensors pickup on the additional weight and, make compensations automatically. For over 8,000 miles, our coach exhibited absolutely ZERO handling effects with that bike on there, what so ever.

No wandering, no porposing, no odd tire wear, nothing. And, this is all with a 36 foot, single rear axle rig. I loved that Hydralift. Without a doubt, the best, most advanced, most efficient, least amount of moving parts lift, on the market. It's a bit on the expensive side but, to me, well worth it. The only reason we changed is because we missed our truck when we sold it. So, we bought a truck, set it up for towing and, installed a Rampage lift/carrier in that for the Wing.

When that Wing was on the back of the coach, the front end came up a whopping 1/16th of an inch. Wow. Pretty tough to get even an accurate measurement with that tiny amount of difference. I'm really surprised that, with a coach as long as yours, and A TAG AXLE TO BOOT, that you get any, noticeable riding/driving characteristic changes what so ever. Especially with the GVWR and GAWR that you have. When we decided to sell that Hydralift, we sold it to gent on the other side of the U.S. from us. So I shipped it to him and, he installed it exactly like I did and, hi coach too was a tag, 42' coach.

After the install and, some initial test runs, he reported ZERO handling differences and road operation characteristics from when the lift and bike wasn't on there.


With ride height controllers, I would think you wouldn't be able to notice anything. Oh well, no biggie. Good luck on your endeavor.
Scott
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Old 04-20-2016, 07:04 PM   #10
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I spent a lot of time determining what ratio for the drive/tag distribution was correct. Not sure what Fleetwood used on the OP's, but Tiffin used a 60/40 proportioning valve that as Turtlekent stated had the front axle at max rating. I had Tiffin replace the prop valves with manual regulators three years ago and mounted them with gauges at the rear for easy adjustment. After several six position weighs, I found the 75/25 was the correct ratio for the wheelbase of the 43QGP. I passed my results on to Tiffin and they made a change in their production. I sometimes tow a 12,000# trailer with a 1500# tongue weight. It turns out that with the trailer weight, the 75/25 ratio was still correct. To do that I have to increase the tag bag pressure from 38 psi up to 50 psi. By changing the amount the tag is carrying, the steer axle remains the same with or without the trailer. Tiffin used a 22,000# drive and a 13,000# tag, so I have a lot more leeway than the 20,000/10,000 combo that Fleetwood used.

After you weigh all three axles, you will be able to determine what ratio prop valves they used. It's possible that you won't have to do anything if you have the right ratio valves.
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Old 04-20-2016, 09:46 PM   #11
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oops
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Old 04-20-2016, 09:53 PM   #12
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oops
LOL !

I had started replying to your original post, so I will continue.

44,600 GVW chassis..... there should'nt be a weight issue!
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Old 04-20-2016, 11:30 PM   #13
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Lol.... The more I read the product I was going to wouldn't do anything

Thus the oops
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Old 04-21-2016, 12:10 AM   #14
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Quote:
Originally Posted by Crasher View Post
I spent a lot of time determining what ratio for the drive/tag distribution was correct. Not sure what Fleetwood used on the OP's, but Tiffin used a 60/40 proportioning valve that as Turtlekent stated had the front axle at max rating. I had Tiffin replace the prop valves with manual regulators three years ago and mounted them with gauges at the rear for easy adjustment. After several six position weighs, I found the 75/25 was the correct ratio for the wheelbase of the 43QGP. I passed my results on to Tiffin and they made a change in their production. I sometimes tow a 12,000# trailer with a 1500# tongue weight. It turns out that with the trailer weight, the 75/25 ratio was still correct. To do that I have to increase the tag bag pressure from 38 psi up to 50 psi. By changing the amount the tag is carrying, the steer axle remains the same with or without the trailer. Tiffin used a 22,000# drive and a 13,000# tag, so I have a lot more leeway than the 20,000/10,000 combo that Fleetwood used.

After you weigh all three axles, you will be able to determine what ratio prop valves they used. It's possible that you won't have to do anything if you have the right ratio valves.
I drag only a toad, so no additional weight on the rear, but I concur with all your numbers. 38# seems to produce an ideal tag weight. I've not been able to get corner weights yet, but I used the dog food scales extensively(38 weighings) for single side weights, and am satisfied each axle is within 200# side-to-side.
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