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Author Topic: Smart Weigh  (Read 2614 times)
wagwar
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« on: September 23, 2012, 09:04:59 AM »

I had my MC 9 weighed at Escapade by Smart Weigh (which is a new program of the Escapees club). Amazingly, it's not overweight (yet?). However, they said the front axle is maxed out and that I should try to reduce the pressure in the tag axle air bags and the tag axle tires to help. How do I change the pressure in the tag axle air bags? Is there an adjustable regulator? Where would I find it?
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« Reply #1 on: September 23, 2012, 12:42:53 PM »

There is an adjustable regulator on the bulkhead above the blower. It should be set at 35 psi. Keep in mind if you decrease the load on the tag you are increasing the load on the drive axle. It will also effect your braking performance. Too light on the tags and the brakes on the tags could easily lock up.

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There are three kinds of people in this world....those that make things happen, those that watch things happen, and those that just wonder what the heck is happening. Which one are you?

1977 MCI Crusader MC-8
8V71N/740
95% converted (they're never really done, are they?)
wagwar
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« Reply #2 on: September 23, 2012, 04:26:45 PM »

I found the regulator. Actually there are two of them - one for the tag and one for the tag unload - 35 psi and 15 psi respectively.  How do I adjust the pressure? 

Just as you said, they also said that too little weight and the tag brakes might cause the tags to skid. Is there a way to adjust the brakes to compensate?

TIA
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TomC
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« Reply #3 on: September 23, 2012, 09:58:37 PM »

I would leave everything alone.  How maxed out are you on the front axle?  What tires are you running?  As long as you have enough pressure in the tires to support the load, don't worry about the axle or air bags-they are WAY over rated.  I know in California, the DOT only looks at the tire to make sure it can carry the load.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
buswarrior
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« Reply #4 on: September 24, 2012, 07:29:08 AM »

Please post all three of your axle weights.

There might not be anything wrong.

I am quite suspicious of the folks who gave that "advice" to you.
Sounds suspiciously like home spun theorists to me.

Lightening the tags WILL induce sliding tires under braking, then you get to listen and feel the flat spots going thump thump thump until you go mad. And then flat spot your new tires at the first short off ramp.

Depending on what the rest of the weights are, my first move might be to take inventory of the stuff that can move, and wonder how much further back in the coach I can store it, instead of where it is now?

Lets see the weights before you take action.

happy coaching!
buswarrior



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wagwar
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« Reply #5 on: September 24, 2012, 08:50:21 AM »

The numbers as I understand for a 1981 MCI MC9. My tires all around are fairly new (0409 and 0712 DOT date code) Firestone FS 560 Plus Load range H, running 110 psi in all eight.

GVWR: 36500
Front GAWR: 13340
Drive GAWR: 22000
Tag GAWR: 6000

My weights:
Front GAWR: L front - 7100   R front - 6300   Total - 13400
Drive GAWR: L rear - 9925   R rear 9150   Total 19075
Tag GAWR: L rear - 1800  R rear  1760  Total  3560

Since I am maxed out on the front, the suggestion was to reduce the pressure in the tag air bags and the tag tires to shift weight towards the rear. They also said that this could cause the tags to skid under braking and that I need to look for a way to adjust the proportion of braking that is applied to the tags.

According to the inflation charts that I found at Firestone web site the following inflation pressures are indicated (to the best of my understanding):

Front: 115 psi  Drive: 75 psi   Tag: 70 psi.

Thanks for your help!
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TomC
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« Reply #6 on: September 24, 2012, 09:21:40 AM »

You didn't mention the most important fact-what size are your tires?
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
wagwar
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« Reply #7 on: September 24, 2012, 04:08:18 PM »

12R22.5
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challenger440
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« Reply #8 on: September 24, 2012, 08:14:27 PM »

Wagwar, don't know if you know the answer to this but are all of these old MCI's that heavy up front.  Or do you have a bunch loaded  on the front half of the bus?  Two chevy pickups worth of weight on the front end seems like a lot.  J M
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buswarrior
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« Reply #9 on: September 24, 2012, 08:30:59 PM »

Nope. I wouldn't do it.

Leave the suspension alone.

And, at those weights, there is no need for an over reaction to this new-to-you information.

But, this is a good warning to other busnuts.

In order that others may do some comparisons and then be inspired to do some weighing of their own...

Please share with us where your fixed equipment has been installed in the coach and the capacities?

Generator, water/waste tanks, granite/marble treatments, auxiliary fuel tanks, etc

And then you can have a CASUAL look at what you store and where in the bays of the coach, and in which cupboards upstairs.

How many things could CONVENIENTLY be simply moved around a bit?

Shift the heavier things way back, and the lighter things forward?

You'd be amazed at what shifting the tool collection to the back of the 3rd bay from the front of the 1st bay can accomplish. And the canned goods to under the bed down the back.

Even moving a set of house batteries to the rear wall of a bay from the front wall has an impact on the front axle loading.

As time passes, one thing to think hard about is to be sure to keep good tires on the front axle, that have some excess carrying capacity beyond those weights, and as you note, kept at the proper pressure for the weight.

And carry on down the road enjoying your coach!

happy coaching!
buswarrior

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wagwar
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« Reply #10 on: September 25, 2012, 08:47:27 AM »

Thanks to all.

I'm not too surprised that the front end is heavy. This bus was mostly completed when I bought it and nearly all of the decisions re: placement of heavy items had already been made. However, to be more specific here is why I am not too surprised the front is heavy:

Up front, immediately behind the front wheels I have a 12' slideout and the 6KW Power Tech generator (now DOA) on the driver side.  Just in front of the forward most bay over the center line in the old A/C condenser bay I have six AGM 8D batteries. In the front bay is the Aqua-Hot near center and a 40 gal aux. diesel tank on the passenger side. The 165 gallon each fresh and black tanks (no gray) are in the 3rd bay back in front of the drive axle.

There are several granite countertops, but none near the front of the bus.

These weights were taken with a full main tank, full aux. tank and full fresh water tank and empty black. While I intend to travel with the fresh tank at 25% most of the time, the bus is not completely set up for full timing yet as we still need to move personal items like clothes, food, etc. However, most of those items will be in the rear half. So, the only other large load that is not yet in the bus and could affect the front axle are my tools. Unfortunately, there are only two places for that - the front bay or the middle bay. Third bay back is full of tanks and water system.

That said, the steers are brand new w/ 0712 DOT date code. if I leave the suspension as-is, would it help to reduce the pressure in the tag tires?

Would you agree with the Smart Weigh folks that while I am not overloaded on any axle, the front has about all it should have. So, the issue is: besides moving stuff around in the bus, which is going to make a marginal difference, is there a safe and advised way to 'pivot' some of the weight back by changing something on the tag axle?

TIA
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TomC
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« Reply #11 on: September 25, 2012, 12:28:54 PM »

I realize you have Firestones, but in my Michelin book (same as Firestone-just checked), your 12R's should support up to 14780lbs @ 120psi.  You could change to 315/80R-22.5 that will support 16,000lbs on a 8.25" wide wheel and 18,000lbs on a 9.00" wheel.  315's ain't cheap, but it will be the easiest way to get more tire capacity.
Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Brian Diehl
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« Reply #12 on: September 25, 2012, 05:51:07 PM »

On my 96A3 - similar to the MC9 chassis - MCI recommends the tag axle to be set at 5000 lbs.  So, at 3700 lbs you are already light on the tag.
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buswarrior
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« Reply #13 on: September 25, 2012, 06:24:58 PM »

Now that you know you are close, I'd just leave it alone and enjoy the hobby.

Unlike many busnuts, you also are clear that good steer tires are important on your bus conversion, just like a fleet coach...

You don't think that your coach went down the road lighter than that in revenue service?

In the old days, the Friday night midnight line run to the north was loaded with the big weekend newspaper, hot off the presses. Two and a half bays completely full of newspaper bundles, a full 47 passengers, and the rest of their weekend luggage that wouldn't fit underneath, up in the coach in the parcel rack, on the floor, under the seats, up the aisle, wherever it would fit. These were in MC7 MC8 and MC9, and it went on for decades.

And that was running on Goodyear bias ply High Miler tires...

I will repeat, forget about suspension adjustments, enjoy the coach, be somewhat thoughtful to put your remaining heavy stuff towards the rear.

As a bonus, your coach will handle really well in the snow, and I am envious of that!

happy coaching!
buswarrior





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« Reply #14 on: September 26, 2012, 05:43:13 AM »

Now that you know you are close, I'd just leave it alone and enjoy the hobby.

As a bonus, your coach will handle really well in the snow, and I am envious of that!
buswarrior

Good Grief, BW, why would you want to drive in that stuff.  It's messy, gets the coach dirty, is full of salt, and usually accompanied by cold.  That's the reason for a bus!  Go South!

Wagwar, you got some really good advice.  And some hints i took seriously as well.  I know when we got ours weighed, I did readjust the boggies, and it did help some, but i paid more attention to where we placed things when we could change it.
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Tom
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« Reply #15 on: September 26, 2012, 08:08:14 AM »

Thanks so much for your help and advice! It is very much appreciated. I'll just adjust the tire pressures as recommended by the mfg charts and get on down the road!
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wagwar
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« Reply #16 on: November 22, 2012, 11:56:51 AM »

I'm installing a TPMS and I'm ready to program the sensors for each axle and wheel. I posted an earlier thread discussing "Smart Weigh" and regarding axle weights and adjusting the tag air bags. The advice was to leave the suspension alone. So I did.

Based on the weights below and the charts I found at Firestone, does it make sense to adjust the tire pressures as follows:

Front: 115 psi  Drive: 75 psi   Tag: 70 psi.

Bus Weights:

The numbers as I understand for a 1981 MCI MC9. My tires all around are fairly new (0409 and 0712 DOT date code) Firestone FS 560 Plus Load range H, running 110 psi in all eight.

GVWR: 36500
Front GAWR: 13340
Drive GAWR: 22000
Tag GAWR: 6000

My weights:
Front GAWR: L front - 7100   R front - 6300   Total - 13400
Drive GAWR: L rear - 9925   R rear 9150   Total 19075
Tag GAWR: L rear - 1800  R rear  1760  Total  3560

Thanks
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Oonrahnjay
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« Reply #17 on: November 22, 2012, 01:09:35 PM »

    Is it common to have a 800 Lb difference side-to-side on a front axle?  (That's not a complaint or a criticism - just noticed it and am asking the question.  Thanks,  BH  NC USA
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Bruce H; Wallace (near Wilmington) NC
1976 Daimler (British) Double-Decker Bus; 34' long
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bevans6
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« Reply #18 on: November 22, 2012, 01:21:23 PM »

He has a slide-out and a generator on the driver's side of the coach.  Even though the side to side leveling is through the rear axle, the front springs have to deal with the fact that the center of gravity of the bus is offset to the driver's side, hence higher weights.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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« Reply #19 on: November 22, 2012, 02:29:45 PM »

  He has a slide-out and a generator on the driver's side of the coach.  Even though the side to side leveling is through the rear axle, the front springs have to deal with the fact that the center of gravity of the bus is offset to the driver's side, hence higher weights.
Brian   

    Thanks, I figured that there would be a perfectly logical answer.   If someone really cared about balance (or considering a bare bus), would the weights likely be more equal?  I guess tanks would have a lot to do with it, too. 
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Bruce H; Wallace (near Wilmington) NC
1976 Daimler (British) Double-Decker Bus; 34' long
6-cyl, 4-stroke, Leyland O-680 engine

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« Reply #20 on: November 22, 2012, 02:54:47 PM »

Without seeing the tire inflation chart you are using, no one can verify the pressures you list.  However, I would guess since you have looked at it in detail and can do the arithmetic, you would have it right.  I personally like to go about 5#'s over what the chart says since it is better to be a little over than under, and I never really trust the tire gauges.  The TPMS always says different than my gauge anyway.
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« Reply #21 on: November 22, 2012, 07:52:00 PM »

These are my weights on my Mci9 now.
It was 6000lbs lighter as a shell.
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MCI-9
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« Reply #22 on: November 23, 2012, 09:17:13 AM »

I took it from this site: http://www.firestonetrucktires.com/us_eng/load/index.asp

The Medium and Commercial and Light Truck Tire chart - 12R22.5. Unfortunately, I could not find any charts that were specific to my tires: Firestone FS 560 Plus LR H. This generic chart was all I could find.

Thanks for the 5lb + tip. That sounds like a good idea.
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belfert
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« Reply #23 on: November 23, 2012, 09:34:02 AM »

I'm pretty sure that Firestone chart applies to all Firestone tires of that size.  I use that chart for my FS 590 Plus tires in the 11R24.5 size.  Interesting thing is that I replaced the steer tires with Roadmaster tires.  The Roadmaster tire chart has the exact same weight/PSI specs as the the Firestone table for the 11R24.5 tires.
« Last Edit: November 23, 2012, 09:35:55 AM by belfert » Logged

Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
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