## Axle weights

## Axle weights

(OP)

Does anyone know of any software that can be used to determine the axle weights of a truck if the load (in this case a dump body) is know. I would like to try different scenarios as far as center of body to center of tandems is concerned as well as other options, plows wings etc...Mike

## RE: Axle weights

1. Determine the empty vehicle axle loads (typically a

trip to the scales)

2. Determine the differences between the empty load and the

max allowable axle loads.

3. Swing moments about each axle to determine the load

center:

(LCf)(Lf) - (LCr)(WB-Lf) = 0

where LCf = load capacity front

LCr = load capacity rear

Lf = distance to load center from

front axle

WB = wheelbase

4. Apply tests of reasonableness to the results

- typically in a set forward configuration the liming

factor is the rear axle load capacity because the

load center tends to move so far forward that you

can't reach the max front axle load and keep the

center reasonably located in the box.

- in a set back axle the load will tend to distribute

itself fairly reasonably in the load box.

- do I exceed state/county laws

- how do I handle things like heap ratio

- brakes, frame, etc...............

5. The calculations get a little more complex, but the

logic follows with pushers and tags.

All of this being said - your body builder can probably answer all of your questions in a few minutes if you are in process of purchase as can your dealer.

## RE: Axle weights

How can I calculate axle weights if truck has four axles.

For example GVW=31t and load centre of mass is defined.

I know that I have two equations (first equations balance of vertical loads and second balance of moments) but there are four undefined axle weights.

## RE: Axle weights

## RE: Axle weights

That method only works accurately if the axles are closely coupled and on a bogie-type suspension (you would still need to account for the differences in the unsprung weight). A better approach is to consider compliances and solve the problem as a statically indeterminate system.

Best regards,

Matthew Ian Loew

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

## RE: Axle weights

The method that you are recommending assumes equal loads on the ground for each rear axle or not? How is suspension equalization (such as air ride) or lack of it for that matter incorporated into calculations? What do you mean by compliances?

Can you elaborate?

Thank You

## RE: Axle weights

No, the method actually does not assume equal load. That is the limitation of the conventional way of computing the axle loads by taking the reaction at an average position (bogie spring center) and then dividing the load in half for each tandem. A better way for non-coupled axles is to introduce compliances (a composite of the tire and suspension springs may work well) to account for the deflection of the vehicle. You can then solve for the system in terms of the deflection at one axle and the angle of the body. It should be clearer after you have the FBD. Another method is to use Finite Element Method (again using pseudo-springs).

None of these methods account for friction and hysteresis in the suspensions. Some differences in measured vs. calculated values should be expected.

Best regards,

Matthew Ian Loew

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

## RE: Axle weights

Do you know of a book, web site, or tech paper that I can read up on this subject.

Thank You

## RE: Axle weights

Aimed mainly at the (very) heavy haulage market.

A.

## RE: Axle weights

Could you send me an example about tridem truck's calculation.

But that should be considered like that 2nd, 3rd and 4th axles' loads are different.

zeusfaber

I could not reach any software or demo that site. I saw only advertisement.

Regards.

## RE: Axle weights

It is all statics. The derivation of the equations is dependent on the choice of datum elements. I will try to post a general derivation when I am in the office next.

A tridem might be best approximated by just using the clasical method with the reactions taken about the #3 axle and then split three ways if they are sufficiently close together, share spring loads, and have equal unsprung mass.

Best regards,

Matthew Ian Loew

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

## RE: Axle weights

You're right - I don't believe the software is downloadable.

Having said that, I think that if you get in touch with Nooteboom, they can provide a demo on CD ROM.

A.

## RE: Axle weights

The Dutch obviously like their axle weights. Nooteboom's northern competitor, Broshuis, has just introduced a free online axle load calculator at:

http://www.broshuis.nl

A.

## RE: Axle weights

Were you able to send info regarding calculations on Tridem drive trucks? What if tridem drive consists of Independent suspensions on each axle? (Here we are talking about Neway AD378 Barpin). I am actually in need to calculate more accurately the load on steering axle. I have used the average middle-point approach on the tridem drive side, but am not satisfied with results. Thank you.

## RE: Axle weights

## CODE

% k = row vector of axle vertical spring rates (N/mm)

% m = vehicle mass

% xmc = x position of vehicle mass center (mm)

n = max(length(x),length(k));

g = 9.81; %m*s^-2 -- acceleration due to gravity

K=zeros(2,2);

K(1,1)=sum(k);

K(1,2)=-sum(k*x');

K(2,1)=-K(1,2);

K(2,2)=-sum(k*(x.^2)');

F = (m*g).*[1;xmc];

U = inv(K)*F;

z(1) = U(1);

for i=2:n,

z(i) = z(1)-x(i)*U(2);

end

load = k.*z;

The function is linear in the linear displacement of the spring at axle 1 and the cosine of the pitch angle.

Please let me know how my method compares to your result. I imagine the #1 axle load will be similar.

Matthew Ian Loew

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

## RE: Axle weights

good57morning@netzero.com

## RE: Axle weights

Must not have needed the code?

Matthew Ian Loew

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

## RE: Axle weights

rmw

## RE: Axle weights

Sorry I could not give you comparison comments.