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Author Topic: Tread life for tag axle tires  (Read 3813 times)
H3Jim
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« on: March 16, 2008, 12:34:18 PM »

What kind of tread life is everyone experiencing for their tag axle tires?

Mine are now bald, and I only have about 25,000 miles on them.  It seems like I should have gotten more miles from them.   I don't always (only 25% of the time) remove the air pressure from the tag axle suspension bags for those tight turns.  It looks like the steers and drivers should go many times that.  I do make many tight turns, and I can sometimes see the rubber I left on the pavement. 

So is this unusually poor? or somewhat representative of what I should expect.  I weight about 39,000 lbs in current trim.  I could be more careful about always removing air from the tag suspension bags, or even spend the money to install the air lifts so the tags are completley clear of the pavement for those tight turns.  Not sure if its worth the money to up grade to the lifting tag or not.
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« Reply #1 on: March 16, 2008, 02:28:28 PM »

Hi Jim, it sounds like you answered your own question...that you need to take the air out more often.  How long does it take to drain that air?  (Just curious, I don't know.)  Bottom line is that by taking a lot of the weight off of that tag...it will help save the tires.
In trucking, the slower you make a U-turn, the less wear to the 'dragging' tires.  So I would guess that if you failed to take the air off...that by making a very ssllooww turn, you would not scrubb as much rubber off the tire(s.)
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H3Jim
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« Reply #2 on: March 16, 2008, 02:34:54 PM »

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.

Does that sound like way too few miles for the tag tires?  I know they are going to be less, but that does seem awfully short lived to me.
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Jim Stewart
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« Reply #3 on: March 16, 2008, 03:00:34 PM »

Jim, you getting no where close to the wear it should be on the tags most of the people I know that have a Prevost take the steers off and install them on the tags because they don't wear that much.Time to make a visit to Dick Kaiser in Eugene when you travel to Busn USA this year he can put it back on track with the 3 axle alignment   
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« Reply #4 on: March 16, 2008, 03:10:52 PM »

Something isn't right if your tags are wearing that fast.  I moved mine back from the steers when I bought the bus, about 60,000 km ago now.  I put them back there because they were worn out, as far as I was concerned.  They really don't look significantly different now.  I'm going to change them this summer, more because they look bad than because I really think they need to be changed.  I put new shoes on the drivers last summer and that makes the tags look really bad but I don't think they have changed significantly in 60,000 km.  FWIW, I don't pay any particular attention to lifting them.  Occasionally I will lift them to back into a particularly tight spot but we're talking about maybe 2 or 3 times per year for a few minutes that the tags are lifted.  To be honest I can't say that lifting them appears to make much difference as far as I can see - they come clear off the ground & it impresses people who are watching me back up but I can't see a whole lot of difference in how the bus handles.



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« Reply #5 on: March 16, 2008, 03:25:37 PM »

Hi Jim,

Luke regrooved my tags last year. I have clocked 22,000 since then and I see almost no wear in them.

??
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« Reply #6 on: March 16, 2008, 04:52:49 PM »

When I bought the bus, I put all new tires and rims on it, and had a 3 axle alignment done at the same time.  The bus has always been twitchy, but much better since I have loaded it up with more weight.  In the beginning, I had to concentrate ALL the time to keep it in a lane.  But even now I can tell without looking if anything is starting to pass me, even a Honda.I can tell because I can feel the bus get "pushed" a bit from the air pressure coming off the passing vehicle.  And yes, for big trucks I have a reflex to compensate.

I've replaced all the shocks too.  After all that, I suspect there is nothing else but either an alignment, or the bushings in the radius rods.  430,000 miles, but spent the first 390,000 on New Jersey potholes.  The bushings I've had inspected, and they don't look too bad yet.
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Jim Stewart
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« Reply #7 on: March 16, 2008, 05:16:15 PM »

Check the weight on the drive and the tag axles. It sounds like your tags are supporting more weight than they should. (or the drives aren't supporting enough)

Expecially since the drives bottom out when the tags are unloaded. (not enough air in the drives) That would explain the squirmy behavior on the road.

Ed
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« Reply #8 on: March 16, 2008, 05:20:34 PM »

I don't know much about Prevost, GM guy here, but there is most definitely something bad wrong with your bus.  You shouldn't have to fight it that much, shouldn't even notice anything but the largest trucks and then only with a significant speed difference.

It looks like you have looked at all the common remedies but I don't know how you can tell the condition of the bushings by looking at them. Change them out.  In my very limited experience with an old 4104, the radius rod bushings made all the difference and the rears even more than the fronts.  It was one of the least expensive and most effective changes to handling that I ever did.

Len
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H3Jim
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« Reply #9 on: March 16, 2008, 06:53:09 PM »

When I had the bus weighed, the  duals were 17,460 lbs, and the tags were  10,520 lbs.
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Jim Stewart
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« Reply #10 on: March 16, 2008, 07:19:39 PM »

Jim - I don't have my book in front of me - but the ratio from drives to tags looks like its off by about 3k lbs if my memory serves me correct - also when I dump my tags they get an inch or two off the ground on level surface - I don't think that yours should be different from the VIP's - FWIW
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« Reply #11 on: March 16, 2008, 07:33:06 PM »

There was a post on the BNO about this a couple of years ago and IIRC the posters said about 6 K.

 At the time I thought that probably wasn't much more than the tag assembly weighed.

 You might check the archives. Also knowing what it use to be you can check it now, pretty cheap, and know if it's changed. That info and the recommended weights info would help to eliminate one possibility.

HTH, Ed
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makemineatwostroke
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« Reply #12 on: March 16, 2008, 07:38:43 PM »

 Jim  most tags and boogies carry 10% of the GVW per side 40,000#= 4000 each side or 8000# for both
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« Reply #13 on: March 16, 2008, 07:47:25 PM »

I had my MC9 start that squirming stuff once and it took me a couple of months
of searching to find the solution... As it happened I had to make a hard stop and I just
looked in the mirror and noticed that the tags were locking up and smoking.

I went back and rechecked and finally found that the air regulator for the tags was way under pressure and there wasn't enough downforce to keep the tags from locking the brakes up. I reset the pressure to the factory setting and the brake problem was solved. Then I played with the pressure until the handling smoothed out and the squirm disappeared.

The pressure finally came out to about 36 psi and approximately 6,200 lbs loading on the tags. No more drift or squirming and steering is rock steady even with trucks passing on 2 lane roads. ( drives with 2 fingers now. )

Dave...
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makemineatwostroke
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« Reply #14 on: March 16, 2008, 07:55:39 PM »

Jim,your problem is not enough air pressure on your drivers I had this with my BlueBird when you lifted the tags it would drag just another thought for you since you have so much weight on the tags and I think all air ride buses have about the same working principal
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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

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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)

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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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« 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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« 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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« 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
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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!
buswarrior
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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
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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. . .

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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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« Reply #30 on: March 21, 2008, 08:59:25 AM »

mine has an annoying alarm that sounds constantly as long as the air is off the tags.  There is also an indicator light on my dash that alerts me to the fact.
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Jim Stewart
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« Reply #31 on: March 21, 2008, 11:23:13 AM »

Jim,

Just as another data point, we are 24/10 on the back.  If I had a way to do it (I don't), I'd actually move 3/4 ton of that from the drivers to the tags.

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« Reply #32 on: March 21, 2008, 07:46:41 PM »

Oh come on, tekebird.

The busnuts without a background in the commercial transport industry look to this board for help and advice.

And they are left wondering whether they should be lifting/unloading the tags when cornering in order to save tire money.

There might be a question as to whether the calibre of today's commercial driver might not be what we like to think it used to be, but that is clouding the point.

Tags stay down unless I need the extra weight for the drives to get out of the parking lot in the snow.

happy coaching!
buswarrior



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