# weight distribution question.



## Philippft (Feb 16, 2008)

would I be correct in thinking that all the weight on my front axle would be from a point exactly midway between the front and rear wheels and everything in front of the front wheels.

Just trying to improve my mass distribution for each axle.


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## ob1 (Sep 25, 2007)

Not quite. If something was loaded between the wheels, but three quarters towards your front wheels, then the weight would be distributed 75% front - 25% back. Weight behind your back axle would have a levering effect off your front axle, i.e. with a 50% rear overhang this would increase the weight of the item by 50% on your back axle and lever 50% off your front. 

A simple way of working weights out is to divide the distance between your axles into 10% segments and then extend this out to the rear of your van as +10, +20, etc. You can then easily work your weight loadings out which will be a good guide, however, a weighbridge is the only answer for dead accuracy.

Ron


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## 113016 (Jun 5, 2008)

You then need to think about the leverage of weight rear of the back axle.
For example a motorcycle weighing say 150kg on a rear bracket will add much more than the 150 kg to the rear axle and will also take weight off the front axle.
Best bet is to frequently weigh your van including axle weights.


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## lgbzone (Oct 8, 2008)

Not necessarily; it would be the equivalent of from the center of gravity (CG) forwards and i doubt that the CG is in the center of the vehicle or center of the wheelbase. the CG also moves; if you add weight to the rear of the CG, the CG will move further rearwards.

How level the vehicle is will also effect where the CG is.

HTH


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## 113016 (Jun 5, 2008)

Agree, the centre of gravity will move, but also weight well back of the rear axle, maybe a motorcycle or heavy items in a m/h garage will certainly put more weight on the rear axle than their own dead weight.
You cannot really counter this with the weight forward of the front axle such as the engine as this weight never really alters.


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## rayrecrok (Nov 21, 2008)

Hi.

It is a matter of your clockwise moments equaling your anti clockwise moments. :wink: 

ray.


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## lgbzone (Oct 8, 2008)

Grath said:


> Agree, the centre of gravity will move, but also weight well back of the rear axle, maybe a motorcycle or heavy items in a m/h garage will certainly put more weight on the rear axle than their own dead weight.


I agree with that grath and wasn't trying to imply otherwise.

i'm saying that i believe the overall weight on the front axle will be the equivalent of what weight is in front of the CG, bearing in mind a vehicle doesn't pivot on the CG because there are more than one point in contact with the ground.

where weight is placed in relation to the CG (and axles) effects how the weight is distributed to the front and rear axles, putting a 50KG weight directly between the axles doesn't necessarily distribute weight equally between those axles, putting that weight on the CG (assuming the CG is between the axles), will distribute it evenly.

Lee


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## rayrecrok (Nov 21, 2008)

Hi.

Any structural engineers here will show mathematically how it works.

How the clock wise moments balance out the anti clockwise moments, it's fifty years since I did the maths, along with duo decimals :roll: .

I don't know how I have managed to get through life without them. :lol: :lol: :lol: 

ray.


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## lgbzone (Oct 8, 2008)

I think that would be more appropriate when there is a single pivot point which is static and you're determining the forces required each side of the point in order to balance or the leverage. although relevant; a vehicle has two axles both of which are on the ground but have their weight suspended.

If you know the CG of the vehicle it's relatively simple to calculate;

where
w = weight of vehicle
wb = wheelbase
fd = distance of front axle from CG
rd = distance of rear axle from CG

the weight on the front axle = w * (rd / wb).
likewise; the weight on the rear axle = w * (fd / wb).

the distribution as a percentage can be calculated by;
front weight percentage = (rd / wb) * 100
rear weight percentage = (fd / wb) * 100

Test figures can easily be put in a spreadsheet and the calculations performed, change the CG in the spreadsheet by making rd smaller and fd bigger (ensuring they always equal wb when added), and you'll see the weight values and distribution % change accordingly.

I don't pretend to understand it all (makes my head hurt), it's what i've picked up from setting up RC cars for race events, weight distribution and transfer is very important to the handling of the cars etc.

I'm still looking for a fence big enough to sit the hymer on to find the CG :lol:


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## VanFlair (Nov 21, 2009)

Hi Philip

I am with Ray on this one it is all about moments.

If you put 100 kg In the boot 1 metre behind the axle and another 100 kg in front of the back axle at the same distance the turning moments will balance so all the weight (200 kg) will go onto the back axle. By the same argument 50 kg 2 metres in front of the back axle will balance the 100 kg load at 1 metre behind the rear axle and again will add the total weight (150 kg) to the backache only as the moments are balanced. When you add a load between the front and back axle it's weight is shared between the two axles proportional to the distance from each axle in the middle would be 50/50 and 1/4 distance from the front axle will put 75% of the load on the font and only 25% on the rear.

I knew 7 years doing mechanical engineering at night school would come in usefull one day.

Martin


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## Bill_H (Feb 18, 2011)

Does this not depend on the type of suspension your vehicle has? surely, if you have leaf springs then the forward weight will be measured from the point where the front of the leaf spring on the rear axle fits to the chassis? which could well be two feet forward of the rear axle.


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## 113016 (Jun 5, 2008)

Agree again, but as we all know, most vans have their storage compartments behind the rear axles and these do tend to get over loaded by inexperienced drivers.
Just look at the number of vans you see with the rear end sagging.
It's all a question of balancing evenly!


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## 113016 (Jun 5, 2008)

Further to the above, it is not really practical to weigh everything that you put into your m/h and then also measure how far you put everything from each axle, what a pain that would be.
It changes all the time as you water quantity both fresh and grey increases or decreases, the fridge gets filled and emptied, then the wine, tins and even people.
What works for us is to try to keep heavy item forward. All three vans that I have owned have weighed in ok (ish) using this method.
Take it to a weigh bridge with everything you carry loaded and move things accordingly until you have both axles and the gross within the weight limits. 
Then always load in a similar way.


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## grizzlyj (Oct 14, 2008)

Philippft said:


> would I be correct in thinking that all the weight on my front axle would be from a point exactly midway between the front and rear wheels and everything in front of the front wheels.
> 
> Just trying to improve my mass distribution for each axle.


Yes, but only if your axle loads are identical and the vehicle is flat, making the CofG in the middle.



Bill_H said:


> Does this not depend on the type of suspension your vehicle has? surely, if you have leaf springs then the forward weight will be measured from the point where the front of the leaf spring on the rear axle fits to the chassis? which could well be two feet forward of the rear axle.


Not really because its axle loads not chassis loads in question perhaps?

VanFlair puts it well I think


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## lgbzone (Oct 8, 2008)

Hi

It won't let me edit my earlier post as i wanted to highlight something, so i've quoted it here.

where i've stated;

"*putting that weight on the CG (assuming the CG is between the axles), will distribute it evenly.*

I have severe reservations about this, in fact i believe it to be wrong 

Sorry


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## VanFlair (Nov 21, 2009)

"putting that weight on the CG (assuming the CG is between the axles), will distribute it evenly. 

I have severe reservations about this, in fact i believe it to be wrong"




You are right that this statement would be wrong if by CofG you mean centre of chassis, to evenly distribute the load you spread it evenly about the whole area but its still the calculation of turning moments that dictates how this affect the individual axle loadings puting the load in one spot in the centre of the chassis would simply increase the point load on the chassis at that point BUT now we are getting a bit theoretical.

I have hesitated to use the term CofG as I believe that this would refer to a 3 dimensional measurement ie not just a point between the wheels it would be a point in the air someplace inside the box that is the vehicle.

Martin


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## tonyt (May 25, 2005)

Philippft said:


> would I be correct in thinking that all the weight on my front axle would be from a point exactly midway between the front and rear wheels and everything in front of the front wheels.
> 
> Just trying to improve my mass distribution for each axle.


Well you did ask!    

................ and now you know!


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## Philippft (Feb 16, 2008)

tonyt said:


> Philippft said:
> 
> 
> > would I be correct in thinking that all the weight on my front axle would be from a point exactly midway between the front and rear wheels and everything in front of the front wheels.
> ...


Spot on Tony, serves me right! I thought I would get a mixed bag !

Let me try and simplify the question. (Here we go again!)

If I load my motor home and drive it fully onto a weigh bridge I will get the total weight of the vehicle. (simple and straight forward!).

Now here's the fun bit ! How far do I need to drive the front wheels on the weigh bridge for me to establish the true weight on my front axle and by default the true weight on my rear axle, or.........drive my rear wheels on to establish rear axle weight etc., etc.,


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## rayrecrok (Nov 21, 2008)

Hi.

My extensive knowledge of structural math calculations allows me to come to the conclusion..

Just cram the bloody stuff in the van, or as sure as eggs are eggs the first thing you leave at home will be the first thing you need and it ain't there.. :lol: :lol: :lol:

Too much stuff, get a box trailer, worked for me. :wink:









ray.


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## jonasw19 (Jun 11, 2010)

>>Now here's the fun bit ! How far do I need to drive the front wheels on the weigh bridge for me to establish the true weight on my front axle and by default the true weight on my rear axle, or.........drive my rear wheels on to establish rear axle weight

Provided that the motorhome is still level you only need to drive on so that one axle is fully on the weighbridge or load cell, whilst the other still remains off the wighbridge.

Having the motorhome level is important when weighing each axle.

jon


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## tonyt (May 25, 2005)

jonasw19 said:


> Provided that the motorhome is still level you only need to drive on so that one axle is fully on the weighbridge or load cell, whilst the other still remains off the wighbridge.
> 
> Having the motorhome level is important when weighing each axle.
> 
> jon


That's interesting - so, no matter how far you drive those front wheels onto the platform, providing the rears stay off the platform and the vehicle is level, the front weight is unchanged?


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## jonasw19 (Jun 11, 2010)

>>That's interesting - so, no matter how far you drive those front wheels onto the platform, providing the rears stay off the platform and the vehicle is level, the front weight is unchanged?

Correct, as mentioned earlier you are interested in just the overall weight and the distribution between front and rear axles.
You do not have any other point of contact except the wheels so there is nowhere else for the weight to be measured. 
The total weight remains constant which is why you onlly have to make 2 measurements ie 
Total weight and
Any axle

The other axle is determined by subtraction
For tag axles you still only need to weigh 2 things, Total weight and any axle.

For artics it gets slightly more complicated but not much.

jon


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## Philippft (Feb 16, 2008)

jonasw19 said:


> >>
> 
> Correct, as mentioned earlier you are interested in just the overall weight and the distribution between front and rear axles.
> 
> jon


Not quite Jon. I'm after the true mass on each axle, which will tell me about my mass distribution.

Once I have that information I I will be able to make adjustments accordingly.

I am of the view that if I just rest my front axle on the weigh bridge and then drive forward 10 feet with my rear axle still off the weigh bridge , the weight reading's will change!

This has turned into an interesting thread and I'm still no wiser after asking the first question.

However, I do appreciate input from members.


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## tonyt (May 25, 2005)

This gets interestinger and interestinger 

Don't laugh - I've just tried it with our digital kitchen scales, a ruler, a pot of Tippex and an eraser.

.......... the weight at one end does appear to increase as it's moved across the scales?


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## jonasw19 (Jun 11, 2010)

Philippft said:


> jonasw19 said:
> 
> 
> > >>
> ...


The true axle reading can be obtained as I said above. The weigh bridge broadly does not care where you are positioned on it only weighing those axles actually parked on it.

You are not correct in your opinion that the weights indicated will alter by driving forward on the weighbridge unless by doing so you change the number of axles on the weighbridge or otherwise put different ones onto it.

jon


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## jonasw19 (Jun 11, 2010)

tonyt said:


> This gets interestinger and interestinger
> 
> Don't laugh - I've just tried it with our digital kitchen scales, a ruler, a pot of Tippex and an eraser.
> 
> .......... the weight at one end does appear to increase as it's moved across the scales?


Tony

You haven't quite replicated the problem you need two axles.

Recipe
1 digital kitchen scales
1 rigid board
2 equal size blocksof wood to act as axles
1 suitable object (? can of beans,brand immaterial)

Method
Put the board on top of the blocks of wood onto the scales
Put the bean can onto the board
Record weight

Move the board so that one block is on the scales and the other is on the worktop, you may have to pad out this block to maintain level.

Record weight
Thsi gives you Overall weight
First axle weight
And by subtracting the second reading from the first you will obtain the Second weight.

Repeat with various positions of the blocks.

Finally open can of beans, switch on the toaster and eat the results.

I wish my cold would go away


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## grizzlyj (Oct 14, 2008)

The only variation axle position will give on a weigh bridge (assuming everything is flat) is from how the scales work or their accuracy, but shouldn't be much. This site has some nice info on axle weighing, including corner weights (O crikey :twisted: ), tag axles and trailers, as well as tyre info even if for US RV's.

www.michelinrvtires.com/assets/pdf/RVTiresBrochure.pdf


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## tonyt (May 25, 2005)

Jon

I just tried as you suggested - and result just as you stated! 

You may be interested to know that it works just as well with a can of soup (Heinz) (Cream of Tomato).

I guess it would also work with these, - but they go better with a glass of water rather than a slice of toast. 

Maybe you should give them a try.


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## 113016 (Jun 5, 2008)

Me thinks you guys have too much time on your hands :lol: :lol: 
What happens to the weight of the beans after you eat them :lol: :lol:


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## oldun (Nov 10, 2005)

rayrecrok said:


> Hi.
> 
> Any structural engineers here will show mathematically how it works.
> 
> ...


Any high school kid ought to be able to show you as it's only school maths that is needed.

If a weight is half way between the front and rear axle then the weight will be shared equally between the two axles.

If the weight is dead over the front axle then all the weight will be carried by the front axle.

To solve this problem take moments arount the front or rear axle (or anywhere else if you prefere).


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