Tag Axle Percentage

[BDWilliamson]

Good Morning:

First time poster on here. We have an 06 Allegro Bus 42', Spartan chassis.

I have just put new tires on it, 10 miles on them. What is the recommended percentage the tag should be carrying? My weights are as follows,

RF-7900

LF-6500

RR-7650

LR-6600

Tag on both-3700

This coach is six months new to us, and I feel that is putting a lot of weight on the front tires. I redistributed the weight in the storage, but I doubt that will be enough. We owned a fifthwheel before, so this Motorhome ownership is new to us. I did a search on this but came up empty, thank you,

Bruce

[wolfe10]

Bruce,

Welcome to the FMCA Forum.

Please tell us your GAWR's (Gross Axle Weight Ratings).

Basic starting point is for each axle to be loaded to the same percent of its GAWR.

Some tag axles are easy to change the loading, others very difficult (depends on how the chassis maker set them up).

[medico]

According to Tiffin, on new 43 foot Allegro Buses, the front axle rating is 15600 pounds, rear is 22000 pounds and tags are 13300 pounds.

It appears your front axle is within limits although starting to approach the limits. Redistribution of the cargo might do enough. I am unsure how to change the tags to put more weight on them. It appears they should be adjusted downward toward the road surface which should add more weight to the tags and take some off the front.

[mpierce]

According to Tiffin, on new 43 foot Allegro Buses, the front axle rating is 15600 pounds, rear is 22000 pounds and tags are 13300 pounds.

It appears your front axle is within limits although starting to approach the limits. Redistribution of the cargo might do enough. I am unsure how to change the tags to put more weight on them. It appears they should be adjusted downward toward the road surface which should add more weight to the tags and take some off the front.

If you increase pressure in the tag, it will add wt. to the tag. However, it will also ADD wt. to the steer. And take wt. off the drives.

[kaypsmith]

"mpierce" is correct, decrease pressure on tag will add to drive, and lessen steers!

[wolfe10]

See my post below, now that we have correct GAWR's and correct tag axle weights.

[BillAdams]

You should join the Tiffin forum as well. IIRC there was an issue with front axle weight and adjustments needed to be able to the tag pressure. This is just from memory so I could be totally off base but the folks there have a tremendous amout of knowledge about the product and will be able to get you pointed in the correct direction.

http://www.tiffinrvnetwork.com/forum/

[medico]

If that is the case, then the tags would have even less weight on them with the drives having more weight. The weight distribution seems way off. I would also suspect there are some heavy objects up front that should be moved toward the back. I might check with a dealer to see why the tags are so lightly weighted with the drives and steers handling too much, especially the steers.

[dickandlois]

Like Brett, I'm wondering about the numbers.

Chassis manufactures and coach builders work to even out the load distribution. items like the Generator, Fresh water tank, Fuel tank are located more to the front.

The black and gray tanks where likely empty and tend to be located over the rear along with the batteries, charger / inverter, transmission and engine.

The rear axle and tag set up are hefty also. One would think the starting weight distribution would be quite good.

Rich.

[BDWilliamson]

Good Morning, I will attempt to answer all questions. First the GVWR on the front is 14,300, the rear is 20,000, and tag is 10,000. We had it weighed in March by smart weigh of Escapees, with 3/4 of a tank of fuel. Waste tanks were empty, fresh water full.

Wolfe, how did you arrive at you percentages? With the rear drives carrying 14,250, and the tags carrying 7,450, that seems to me that is over 50%, and if I lighten the load on the tags, it would lighten the load on the front putting more weight on the drives. Am I way off base here?

The weight on the RF exceeded the rating of the tire, at the time Michelin's, now I have new Continental's, Max load single 7160*, which is still over the rating. Like most MH pushers, the 10 KW generator is in the front as well as the 150 gal. fuel tank.

Bill, we are members of the Tiffen network.

We are going to have the MH aligned next Tuesday, and I am hopeful they can shed some light on the tag. Without knowing what I am up against, I value the responses on the forum. We kind of value the fact that we don't travel heavy, but maybe I am wrong. Totally confused, thanks, Bruce

[wolfe10]

My numbers above were based on Medico's posting of GAWR's (did not have yours) and the assumption that "Tag on both-3700" meant 3700 total.

So, will go back and recalculate based on your new numbers:

Front axle: 7900 + 6500/14,300= 101% (i.e. axle slightly overloaded-- with left side well overweight: 7900/7150=107%)

Drive axle: 7650 + 6600/20000= 71.3%

Tag axle: 3700 + 3700/10000= 74%

Conclusion-- lessen the weight on the tag, which will increase weight on the drive axle and lessen weight on the front axle.

Next question: do you have two ride height valves on the front axle or on the drive axle (with the other axle having only one)?

BTW, have set up a number of tag axle coaches-- several going back over the scales a couple of times (after each adjustment) to achieve close to the same percent on each axle-- the Monaco products are quite easy-- an easily adjustable valve in the engine room. Have not worked on your particular chassis.

[medico]

The ratings I showed were, as stated, on a new coach. I did not have any specs for an 06 Bus. I figured they were probably close.

[BillAdams]

It does appear that your front is over weight and you need to adjust the tag pressure to correct this situation. What did the folks on the Tiffin forum tell you related to this particular situation?

[BDWilliamson]

Bill, when I inquired over there, I did not get any kind of informative answer, but it was probably my fault for not asking the right questions, also I did not have my weights then. We are in SoCal. now and I am getting the MH aligned on Tuesday and one of their techs is going to check with Spartan about the tag. I think adjusting my tag properly will take a load off of the front, and also give me more traction on the drives.

Thanks everyone for all the help and input, it helps me to understand this coach better all the time, Bruce

[Cruzer]

We have similar coaches. The front axle is actually a 14,600 lb rated axle, however, with the 275/80R22.5 LRH Michelins you are limited to 14,320 lbs.According to Spartan, you should have one third of the weight on the tag axle and 2/3 on the drive axle so you proportioning valve is set properly. The real issue is that Tiffin put too much weight on the front axle. It took them a few years to figure out how to deal with that as the tag axle Bus was new in 2006.

Now your decision is how to deal with that. A number of owners had their tires upgraded to 295s, which increased the load capacity. Technically the tires were now better than the axle rating but later on the axles were rerated at 15,600 with only a wheel bearing and spindle change, which really wasn't necessary in an occasional vocation situation like a motorhome. One thing to consider is that the Allegro Bus on a Freightliner came with 8.25" wide rims while the Spartan came with the 7.5" wide rims, which are perfect for the 275 tires but too narrow for the 295s. So if you get larger tires you'll need to replace the two front wheel rims as well.

Some owners have played games with the rear proportioning valve. That's a band-aid fix that does serve to lessen the load on the tag axle and shift more to the driver axle. The tag axles is designed to carry lots of weight, which is good, but the downside is that it acts as a lever, pivoting that weight on the rear axle and shifting it to the front (steer) axle. That's why all of the tag axle Tiffins had front weight issues while the 40' single rear axle coaches tended to have overweight issues on the rear axle with light front end weights. If you reduce the tag axle bag pressure by shifting the proportioning valve you will reduce the front axle weight but there's only so much you can go without changing the overall geometry and stability that the chassis was designed for.

It's a tough spot to be in. Our 42QRP "just" makes it on the front axle. Many of the later coaches got worse as they added more Corian, ceramic tile, and other heavy "stuff" to the coaches. That's why Entegra now has a 16K front axle and 315 tires.