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Author Topic: Weight Distribution  (Read 7084 times)
WorkingOnWise
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« on: April 17, 2007, 06:08:40 AM »

In another thread I discussed weight distribution and the effect on vehicle handling and ride quality. I'd like to know what your thoughts are on the following.

I know that this coach will always be a very heavy and lethargic machine, compared to my little 5000lb pickup. My goal is to improve safety and handling and ride quality by removing and redistributing weight, moving weight forward of the rear axle, and as low as I can get it. Ideally, the lower the weight is and the more evenly distributed it is both front to back and left to right, the better it will handle and ride. I do understand that there is an issue of suspension and tire capacity, the rear being the stronger. That said, the front can handle a good bit of weight more that my gutted coach is putting on it.


As an example, a few hundred pounds wont matter unless they are in an area where it act like a lever, as does all the weight aft of the rear tires. 125lbs removed from the centerline of the engine removes 400lbs of weight from the rear tires. I must remove 400 lbs from just in front of the rear tires to have the same effect. I know it sounds wrong, but it's in the leverage and position of the weight. The vehicle weight will only change by 125lbs if I remove 125lbs, but the balance of the vehicle will change by 400lbs. The weight aft of the rear tires acts as a lever to not only push the rear tires down, but also to use the rears as a fulcrum for the lever to lift the front tires.

One more example. I have seen talk of moving the start batteries back to the engine compartment to remove that 3 mile point of failure known as the starter cables. Electrically, we agree it is a great idea. Less cable and less intrerconnect point makes for a more reliable system. But to do that also moves 160-ish lbs of Group 30's back behind the rear tires, countering what I want to do. The factory 8D's together weigh about 300-ish lbs, so it is possible that the effective weight of the move would be neutral. But in moving the batteries there, first you have removed 300lbs from about the middle and left side of the coach, and at best added only 160 lbs to way back there, to act on the front in the lever fashion I explained above. It will actually have a negative effect on handling.

This one change, if it were the only one, would go totally unnoticed. But it isn't the only change I'll be making. It's one of thousands, each one effecting the handling of the finished coach. I'm not going to worry about the location of a light fixture in relationship to vehicle balance, but anything ofer 100lbs will be looked at in the light of balance, as well as feasibility, ease of use and serviceability.

Gimme a minute to don the fire suit, then lets hear it.

Thanks
Keith
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tekebird
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« Reply #1 on: April 17, 2007, 06:44:07 AM »

I understand your concept....... and my vector analyisis days are long gone from my brain for the most part.

Noew to your probelm.........moving the batteries to the engine comaprtment is generally something done on something other than a GM........the transverse engine layout and lack of floor or accesable "frame" does not lend itself to that.


More often that not I think this move is made to free up space more than saving any reliability issue....read RJ'S post in your other thread on reliability by design.

no for my silight recall of vectors.  Keeping in mind.....that the engine is hanging from the roof and the bottom of the Firewall bulkhead.  There are forces from everything aft of the drivers that I am sure can be measured at the windshiled frame due to the nature of a monocoque design

Now does this not put most forces  down on the drive axle perhaps with a slight angle bias towards the rear of the bus....so a bit of Lever action?  Or stating it differently.......if the wieght is actually 5 foot from the axle.......but the forces are transfered into the roof anf the firewall, the force is not actually at 5 foot but  some fraction of 5 foot thatt is much closer to the axle......thus its lever effect is much less than the calculation you quoted.. True it is not 0.

Unlike 500 # hanging off the rear of a frame vehicle where all the force is down from the location of the weight?

Once again,  Anything close to normal you might do will not be noticed in handling of the bus.  There are guys running around with GM's towing 20,000# trailers with 2000# tongue weights, despite the structure not being dddesigned for that........and despite there being known failures from this sort of application and none of them note any gross loss or change of handling.

Again it's not a race car.........



Example: An empty City bus (GM), a group of weight wather dropouts get on........they all choose to sit at the back of the bus......so each of them weighs, 280# and there are 10 of them, 2800# siting rear of the drive axle........does the driver stop and say please move forward so I can keep a proper CG......

Alternate:  that same 2800# of people choose to sit on the curb side..........does the bus lean that direction.....or turn that way better......NOpe. at least not at any noticable ammount.


Maybe me thinks you should have got a used crown schoolbus......then your engine and drivetrain weight would be between the axles and you would not have to fret over it.

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kyle4501
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« Reply #2 on: April 17, 2007, 07:09:07 AM »

WOW, Are you serious?Huh?
This question from the man who knows how to solve the structural issues involved in stretching a 35' bus to 45'Huh??

Gee Whiz
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tekebird
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« Reply #3 on: April 17, 2007, 07:22:02 AM »

Keith,

where did you get you Mechanical Eng Degree?
When?
Where did you get your Elec Eng Degree?
When?
Where did you get your Master Automotive Mechanic Cert?
When?


The whole statement that you have accident reports with data from Fishbowl Accidents that has data that you can use to design your restructuring is bogus in my eyes.........when the fishbowl was in service they didn't do such things and the Feds had no hand in safety of design......prob because there was no need as the things were built to last and survive.....they did not care about Emmisions and MPG's

best I think you would find if there is a way to search is:

This car pulled out in front of bus
Bus pulled out in front of car
driver had stroke

that type of thing.

I NOW CALL SHENANAGINS
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tekebird
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« Reply #4 on: April 17, 2007, 07:23:28 AM »

To Be Clear

Shenanagins= BULL SH!T
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Hartley
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« Reply #5 on: April 17, 2007, 07:31:53 AM »

Who cares,  Huh Huh

Just fill it until you get 12 to 14 thousand on the front tires
and 23,000 on the rear.

All this talk of performance, handling and that nonsense has absolutely nothing to do with a BUS !

These are all NON-ISSUES... It's a flipping BUS ! Undecided Undecided

This is surely starting to sound like another one of those guys just jerking us around to see how far
we will "BUY" his "STORIES"... 90% of it is completely unrealistic.

Just a load of "BULL-PUCKEY", Hope you are having a good laugh over this mister genious. With all of the "dreamer" qualifications
you seem to have why are you messing with "the great deal $100 bus"?

 Shocked Shocked Shocked Shocked Shocked Shocked Shocked Shocked Shocked Shocked
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WorkingOnWise
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« Reply #6 on: April 17, 2007, 07:58:06 AM »

Ever roll a vehicle or trailer because it was top-heavy? I have. It Sucks!
Ever do a 180 because the bed of the truck so light the rears had no bite? No fun.
Ever slide into a ditch because the back end was so heavy that it pushe you there?
Ever overload a trailer to the point that the front tires didn't brake right? Lock up easy? Flat out scarry! Just glad the trailer brakes worked.

It's a bus...so physics don't apply to it? Thats Pucky!
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tekebird
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« Reply #7 on: April 17, 2007, 08:15:13 AM »

Physics do aply.....but the  slight weights you are talking about will make no damn difference.

what are your feers as far as the buses poor handling?

you are not going to spin out ftrom lack of traction.....

slide into the ditch becasue the back end pushed you there.......thats BS...it's because you were driving to fast and trying to stop to fast.

Outside of packing the back of the bus with lead your not going to reduce the weight of the front end to do what you are concerned about.

Roll a vehicle or trailer because it was top heavy.........once again you contradist your claimed training.......why did you load it top heavy, why did you drive it outside it's capabilities.

Continued BS

Since you are an engineer lets sstop talking vaguely and in laymans terms.....there are other people on here with techincal experience in the Automitive industry, aviation indeustry etc.......talk facts and figure with your ideas and concerns or stop talking out your butt.

Lets go back to the vector analyisi on the 125 lb fan clutch and rework that as your calculations are incorrect for the monocoque design

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Lee Bradley
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« Reply #8 on: April 17, 2007, 08:28:45 AM »

Ever roll a vehicle or trailer because it was top-heavy? I have. It Sucks!
Ever do a 180 because the bed of the truck so light the rears had no bite? No fun.
Ever slide into a ditch because the back end was so heavy that it pushe you there?
Ever overload a trailer to the point that the front tires didn't brake right? Lock up easy? Flat out scarry! Just glad the trailer brakes worked.

It's a bus...so physics don't apply to it? Thats Pucky!


Those are all operator errors.

Dr Dave,
I think you're right; we may have a troll infection.
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WorkingOnWise
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« Reply #9 on: April 17, 2007, 08:56:33 AM »

um..ok boss.....sorry.

People do dumb stuff some times. Me, and others. I don''t need a vehicle that is so poorly balanced that I must tailor my evasive maneuvers to the unnecessarily low limits of the coach and the situation at hand, thats all.
I learned at 16 about proper weight distribution, after I was repacking stuff into a second trailer, the right way, after rolling it. Fortunately (?) the hitch snapped and trailed gently slid into the ditch. The car was fine.
Yeah, the slide into a ditch and the overloaded trailer were all me.
The 180 however, was a result of a bonehead in a 4x4 doing 65 on an ice-covered road, passing me who was going 35 along with everyone else, losing control, and sliding in front of me. I had nowhere good to go, so let off the gas (had to lose speed somehow) and tried to steer around him. I slid sideways and then around, scrubbing off enough speed that we never touched. While the 180 was helpful, it is Not the way I would have chosen to avoid the collision. That same situation in a bus would have put a 35' road block, or 65' with a trailer, with much more momentum that my little truck had. The result would not have been as clean had the bus spun. In a bus, I would have simply held the wheel straight, held the gas steady, and hit him with my big black rubber bumper, hoping they would save the coach from too much damage. The truck sliding in front of me would have been an afterthought.
unloaded pickups are very poorly balanced.
Poor balance shows fastest when you are least able to do much about it- at the limits or available traction.

The point being, a poorly balanced vehicle of any size is dangerous.
Ideally we should never get into a situation where it is a problem. In reality, we are not always so blessed.
As for your statements about the calculations being incorrect for the monocoque design, while I do not fully agree, I don't know for sure, so I will test it and let the model show me.

As for crash data, you assumed I meant some agency source it sounds like.
The data I will have to use comes from
1- a model of my coach, with information on metallurgical properties from knowing what metals are there, which I still have to get. That gives me the baseline.
2- Crash reports involving 35' fishbowls with 6v71's and 2sppd transmission. The reports all say the speed range of the impact, and what angle, and what what the other object was. I'll be looking for collisions with stationary objects. I'll run several of those scenarios against the baseline to be sure my model is accurate. Then I'll build the model as I want to modify the coach, and run the same scenarios, and compare.

There are other forms of data available than what is spoon fed. With stuff this old, yeah,, I'll have more work that just googleing for it.
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TomC
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« Reply #10 on: April 17, 2007, 09:21:47 AM »

From my 1.3 million miles of driving, I'll tell you that weight overhang in the back of the trailer does make a difference in ride quality.  But-not what you think.  Take a semi-trailer that is loaded such that you have to run with the rear axles slid all the way back compared to when the trailer is loaded such that you have to run with the rear axles slid all the way forward (about 10ft).  When the axles are slid all the way forward, with the extra weight behind the axles, the bouncing action of the trailer is much slower and rides much smoother. This is the same theory with buses.  Weight on the overhang of the bus makes the oscillation of the rebound much slower and more enjoyable to ride in.  That's one of the reasons I installed my 10kw generator (about 600lb total) in front next to the drivers seat like a front engine.  Also, before building, I went through and did a side to side weight estimate and decided to put the kitchen on the left side along with the reefer, washer/dryer, furnace and propane tank, and the bathroom on the right side (it is built around the rear door so to have direct bathroom access from the outside) along with my 2-8D batteries and 100# freezer.  I ended up with the bus a few hundred pounds heavier on the left-just like I wanted because of the crown in most roads, and the axle weights are 10,500lb front and 20,500lb rear-which is no where close to the 13,000lb front and 23,000lb rear axle ratings.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
WorkingOnWise
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« Reply #11 on: April 17, 2007, 09:44:59 AM »

I have only driven a semi-trailer 2 times, for maybe 300 miles, so I have 0 knowledge of trailer axle position vs. ride quality. I can see how the overhanging weight could improve ride. I has a 77 Lincoln Mark 5 and a 460, hydraulic boost brakes, and every weight adding option ford offered. It was a heavy beast, and there was lots of weight past the front and rear tires. And it rode great, even with stiffer springs and tighter shocks
Heres a question TomC
How does that weight in the overhangs affect handling, compared to the same weight moved to between the wheels, and closer to the center.
It sounds like you know a bunch about driving very heavy vehicles. My experience is from cars. Much smaller. I assumed that the dynamics are the same, just bigger numbers.

Thanks
Keith
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kyle4501
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« Reply #12 on: April 17, 2007, 09:58:55 AM »

Why not run it thru that stimulation computer, then you will know the exact optimum location for everything in the bus.  Grin

Seems like you could load the bus up with a bunch accelerometer sensors & data recorders.
Drive a given route several times to establish a good base line.
Add weight & repeat the route.
Move the weight & repeat.

The results can be studied to determine optimum placement for best ride.


The car & class 8 trucks have different frame design & as a result the specific dynamics will be very different.

But you knew that already.
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TomC
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« Reply #13 on: April 17, 2007, 10:02:15 AM »

At a certain point, too much overhang weight can cause the tail to wag the dog (how many times have you seen a sticks and staples with the drive axle just about in the middle of the motorhome with a tag behind and a monster amount of rear overhang?  Then they are pulling a car too-they are braver than I am).  On a bus, you typically will not have to worry about the weight issue.  The one bus that comes to mind with a lot of rear overhang is VanHool.  I did see one get hung up with the wheels in the air coming out of a driveway, but once again that is driver error, since he should have taken it at an angle, or even back out instead.
With weight past the rear axles, it will slow the oscillations of the bus.  I installed 3 roof airs that added about 330lb to the top of the bus.  I did notice a bit more rocking action compared to without the A/C's, but not bad.  The transits don't have those big anti sway bars for nothing.  With a conversion, it would be very hard to overload the bus unless you were to put an exorbitant amount of marble, slate, granite, with very heavy furnishings.  I know Newell on their latest 45ft'r weighs in at a whopping 54,000lb, but also has a 62,000lb gvw (18 front, 26 drive, 18 tag).  So their 625hp Caterpillar with 2050lb/ft torque going through the ZF 10spd Freedom transmission has its' work cut out.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Don4107
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« Reply #14 on: April 17, 2007, 03:37:46 PM »

If I removed 125# from the engine of my 4107 the result would be about 150# less on the rear and 25# more on the front axle.  Net change of 125#.  A basic 4-1 lever.  Engine is about 5' behind the axle and about 20' to the front axle from the rear axle.  Don't see how you arrived at 400# at the rear.  Is Al Gore a relative? Roll Eyes

My bus is designed to have around 1000# change near the front axle between full fuel and low fuel.  I doubt that there were any passenger/baggage loading restrictions to keep the bus 'stable'.  Short of putting a couple ton on the roof I don't think there is much you could do to change the handling substantially other than tires and shocks.
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