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Author Topic: Tread life for tag axle tires  (Read 3822 times)
Sojourner
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« Reply #15 on: March 16, 2008, 08:00:38 PM »

Jim...According to your weigh given...it should be readjusted to 18653 # for dual and 9327 # for tag. Always divide total rear weigh of two axles into number of tires.

That  alone will explain squirrelly driving.

And yes to release tag air while sharp turning.

FWIW

Sojourn for Christ, Jerry
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Stan
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« Reply #16 on: March 17, 2008, 06:17:50 AM »

Quote
easy to do, just a lever by the driver and it takes about 2 seconds, maybe 5 to 10 to fill back up.  But it sets off a beeper, and for some corners, since it makes the rear drop as it does not allow any additionoal air to go to the driver bags, and it makes me bottom out.

There is something strange with this statement. The rear ride height is set by the leveling valves (on the drive axle) and should be the same regardless of tag position. When you dump the tag air, the leveling valves should immediately put more air into the drive axle bags.

If your rear ride height is too low, you will have excess weight on the tag axle. Your problem may be as simple as adjusting the rear leveling valves. HTH
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H3Jim
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« Reply #17 on: March 17, 2008, 07:32:49 AM »

Niles, my bus does not have the lifting option on it.  It takes the weight off the tags, but the lifting air bags and the chains are not there. I've not priced them, but I know they won't be cheap.  I thought that jsut removing the weight would be good enough.

Regarding the dropping when I remove the tag air - I supsect there is some control system that prevents additional air from being added to the drive bags.  Yes the leveling valve lever is moved, but there is never any air that's added to the drive bags no matter how long I sit like that.

How do you adjust the weight on the tags?
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Jim Stewart
El Cajon, Ca.  (San Diego area)

Travel is more than the seeing of sights, it is a change that goes on, deep  and permanent, in the ideas of living.
makemineatwostroke
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« Reply #18 on: March 17, 2008, 07:43:30 AM »

.

How do you adjust the weight on the tags?
[/quote]


Jim, on my BB the air pressure was set at so many pound for the tag and you adjusted the weight on the tags by adding air to the drivers to remove the weight on the tag not sure if Prevost works the same or not  good luck
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Stan
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« Reply #19 on: March 17, 2008, 09:23:42 AM »

MCI called for 2/3 weight on the drive axle and 1/3 on the tag which gives equal tire loading. The ride height is set by the drive axle leveling valves and the tag weight set by a pressure regulator on the tag bags. Any change to one will affect the other so it takes some back and forth to get the proper distribution.

If your bus cannot adjust the drive bags when the tag is unloaded it may use a completely different method. It might be worth a phone call to Prevost for the answer.
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Sojourner
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« Reply #20 on: March 17, 2008, 10:33:12 AM »

Niles, my bus does not have the lifting option on it.  It takes the weight off the tags, but the lifting air bags and the chains are not there. I've not priced them, but I know they won't be cheap.  I thought that jsut removing the weight would be good enough.

Regarding the dropping when I remove the tag air - I suspects there is some control system that prevents additional air from being added to the drive bags.  Yes the leveling valve lever is moved, but there is never any air that's added to the drive bags no matter how long I sit like that.

How do you adjust the weight on the tags?

----------------------------------------------
PS...Thanks Stan for your post....You beat me to it while I was typing this.
----------------------------------------------

Your operator manual should point out the tag's regulators adjustment in your Prevost.

About lifting option: It not needed but just by releasing tag's air will let it slide to about 95% less fiction to save tread wear. Your Prevost should or could have air relay switch inline toward tag's rolling lobes. If not...install one with electric solenoid valve that is rated 200 psi or one after each air regulator that is rated 50 psi with 1/8” orifice.

Regarding the dropping when I remove the tag air:
I assume that it never corrected the drop.
You need to look at the rear drive axle leveling system....either it has air regulator inline to the leveling valve that need to increase or it already to the load limit for rear drive axle's rolling lobes or problem with leveling valve that needs attention.

Bottom line that it should be able to maintain its adjusted height unless you’re over loaded with no air in tag's rolling lobe bags. Tag wheel are mainly to carry the overhanging of engine & transmission assembly weight for 40' or longer.

Let us know what your or anyone's manual say about adjusting tags rolling lobe pressure.

Because this is motorhome…not a passenger coach with greater weights variable.
I believe to properly adjust MCI or Prevost tag wheel is to weigh the total 6 wheel contact pressure on scale with front wheel on level plane of scale's surface.

Then divide the total 6 contact weights that will give you the adjusted requirement for each tag's wheel.

Example total 6 wheels contact weight is 30000 lbs. Divide 30000 lbs by 6 equal to 5000 lbs. 

Now move coach's drive wheel off scale but leave tag wheel on scale and  readjust both tag’s regulators so it very low or no psi.

Then readjust one tag's air regulator until it weighs 5000 lbs and adjust the others side tag's air regulator until it weighs 10000 lbs on the same parking spot.

Now you should have equal balance of load of each wheel & tires.

The manual may say more or less tag air pressure but tags should never be more contact pressure than each of the dual contact pressure.

FWIW

Sojourn for Christ, Jerry

« Last Edit: March 17, 2008, 10:40:22 AM by Sojourner » Logged
niles500
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« Reply #21 on: March 17, 2008, 12:49:00 PM »

Okay - finally got to the office - Da Book says on my H3-40 (think your a 41?)

GAWR
Front - 13,000
Drive- 25,000
Tag- 10,000

I was a little off to say the least - I can never remember to NOT trust my memory - HTH

*** Actually when I do the ratio I was pretty close 35k total/10k tag/25k drive translates to 28k total/8k tag/20k drive - Now I'm confused Huh?
« Last Edit: March 17, 2008, 01:40:45 PM by niles500 » Logged

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Tony LEE
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« Reply #22 on: March 17, 2008, 01:51:53 PM »

"And yes to release tag air while sharp turning"

The MC8 has a turning circle of 28.5metres - 94', so any turn would be considered a wide turn, especially compared with what the triple-axle rear wheels of a semi-trailer are subjected to when reversing into tight corners.

I did some tests on a big empty parking area - turning circle with tags loaded and fully unloaded (using the dump valves rather than the solenoid which only reduces pressure from 35psi to 15 psi). Tyre tracks were virtually on top of each other, so I figure that if the sideways skidding of the tags makes little difference to the turning circle, then it is not going to add much wear either.
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SKIP
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« Reply #23 on: March 17, 2008, 02:01:43 PM »

It's hard to believe that all the wear can be attributed to air pressure. You might want to look at alignment. Yes they skuff on turns and you will see more rubber from them being overweighted, but I would think that you should still see much higher mileage.
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H3Jim
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« Reply #24 on: March 20, 2008, 06:42:40 PM »

When I had the tires replaced and could see them off teh bus, the outside edge was badly worn, while I still had good tread in the center and inside edge.

NIles, yes my H3 is  a -41, and here are the max GVW.

Max vehicle load   
Front    16,500
Duals    22,500
tag    14,000


Not sure you can infer relative tire loading from the max figures, although it works for these.  The duals seem to be twice what the tags can support, twice the tire.
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Jim Stewart
El Cajon, Ca.  (San Diego area)

Travel is more than the seeing of sights, it is a change that goes on, deep  and permanent, in the ideas of living.
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« Reply #25 on: March 20, 2008, 08:58:09 PM »

Hello Jim.

You have a tag axle alignment problem, if the tires are wearing unevenly.

Full stop. End of story.

None of the big fleets are teaching their drivers to lift the tags for cornering to save tire wear.

If there was any savings to speak of, you'd be sure the big boys would be having the drivers do it.

Prevost uses a brake chamber acting on a lever and a piece of chain to lift the tag axle off the ground. Simple, cheap and effective. Lots of snow in the home of Prevost...makes all the difference between getting out of the parking lot, and booking back into the hotel with the group until Spring.

I've done the same turning circle test as Tony Lee, only with a 45 foot Prevost. There are many misconceptions as to what this will improve. With the tags lifted, the complete turning circle dug into the gravel by the duals was only four feet shorter on the other side, a marginal improvement, the use of which on a 90 degree corner might pull the rear over by a foot, if the driver was able to do something with the improvement, which most weekend warriors will not be able to do, and some fair number of regular pedal pushers won't be able to either, so don't feel bad!

The older MCI crowd may have noticed the "shocking" heights that the tag weights are reaching on these Prevost...Being accustomed to F12K, D20K and T6K. The newer equipment is putting greater demands on the tag axle. The 45 foot coaches are rating and loading the tags as heavy as the steers up at 14K!

Jim, before the alignment shop starts, just for fun, tell 'em you want to know how far out it is. They might not take note of the starting point otherwise, and just fix it.

happy coaching!
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niles500
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« Reply #26 on: March 20, 2008, 09:22:11 PM »

Jim - now I'm wondering why the 1 foot difference in our coaches has such a disparity in axle weights Huh?
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« Reply #27 on: March 20, 2008, 10:33:08 PM »

Niles,
Preovst  discontinued the 40 footer at the same time they started making the 45 and the 41 footer.  They had to make the 45 footer to be competitive - as soon as it became legal, everyone had to make one.  They still wanted to make a 40 ish model, but did not want to have two different production lines, so they just made the 41 identical to the 45, but with one bay section removed.  They used the same axle as the 45 etc etc, so the 41 can actually carry more as it has the same axles, but the bus itself is lighter.
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Jim Stewart
El Cajon, Ca.  (San Diego area)

Travel is more than the seeing of sights, it is a change that goes on, deep  and permanent, in the ideas of living.
RJ
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« Reply #28 on: March 21, 2008, 07:34:04 AM »

Jim -

I'll throw in my thoughts here too, just to thoroughly corn-fuzzle the issue:

1. Tag axles are out of alignment.

2. Radius rod bushings are worn and should be replaced - before alignment!  (You said coach had 430K on it - company I used to work for routinely replaced the dog bone bushings at 200K, fwiw.)

3. Leveling valves front and rear should be checked for proper operation and ride height setting - possible front's too high and drive's too low.


Sounds to me like it's time for some suspension pm!

FWIW & HTH. . .

 Wink
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RJ Long
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« Reply #29 on: March 21, 2008, 08:45:59 AM »

the Big Fleets ( greyhoun d etc) are not teaching lifting the tag on tight turns, because the people they are hiring are not bright enough to remember to put them back down
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