Inside spring effect on elastic load transfer?

[adambrouillard]

I've been trying to calculate the elastic load transfer and was wondering how to calculate it.

For a wheel pair, do I add both inside and outside spring together and then add the anti-roll bar or does only the outside spring get added to roll bar. If the inside spring does get added, why is that? It seems only the outside spring is resisting roll.

[Goran Malmberg]

Originally Posted by adambrouillard

I've been trying to calculate the elastic load transfer and was wondering how to calculate it.

For a wheel pair, do I add both inside and outside spring together and then add the anti-roll bar or does only the outside spring get added to roll bar. If the inside spring does get added, why is that? It seems only the outside spring is resisting roll.

Think of the car as a rektangular board with a spring under it each corner. You have weights standing along each side of the board. Take 100p away fom one side and put it on the other side. The board will raise the same amount as it goes down on the ohter side. The board has been rotating about its centre axis, (althrougth there is no axis and bearings).

If we should create the same "rotation" without moving weights but use our hands, it will take the same force to lift the car one side as it takes to press it down the same distans the other side. It is the same work both sides but the sume of the work lands on the outside wheels.

In order to rotate the board the swaybar must be twisted. So the total torsional spring number of the bar must be added to the roll spring rate. The difference between the swaybar and springs is that apart from the springs the swaybar is not loaded at rest, which makes them seem to work together in a tricky manner.
Goran

[Goran Malmberg]

I may add that we could separate the roll motion from the weight transfer situation. The weight transfer is a function of CGH, weight, track width and G-force, only, no matter what the anti or spring-geometry settings are.
Goran

[adambrouillard]

What would be the calculation for apportioning roll resistance then?

Let's say front springs are 300 each and rear springs are 500 each.

Front roll bar is also 300. Let's assume equal track front and rear.

If you use both springs and add the roll bar that would be 900 front and 1000 rear. This is not counting the geometric effect. Is this correct?

[Goran Malmberg]

Originally Posted by adambrouillard

What would be the calculation for apportioning roll resistance then?

Let's say front springs are 300 each and rear springs are 500 each.

Front roll bar is also 300. Let's assume equal track front and rear.

If you use both springs and add the roll bar that would be 900 front and 1000 rear. This is not counting the geometric effect. Is this correct?

To be correct here I must point out that it is the wheelrate that counts. There is a lever relationship from the spring to the wheel that also include a tilt of the coilover or MCP. That motion ratio is to be squared times the spring ratio. This is becouse we are dealing with both a rise of sprung ratio AND lever ratio. So wheel ratio becomes a lot softer that the spring itself.

The rollbar often has strange shapes with angle arms
making it work partley as a transverse leaf spring and could be hard to calculate accuratley.

Now, add all 4 wheelrates together with the 4 wheelrate for the two sway bars and you have the deflection rate in roll of the car.

As for an theoretical (clean) roll situation, the swaybar could be looked at as four independent torsion bars, one each wheel that is welded solid to the car
in the middle. This is becouse when the bar is twisted the same ammount each side (in different directions) it will remain in rest in its middle. This way of looking at the bar might give an better feel of how it works.

Right, the geometric effect is outside of this equation and is handled separatley.

However, a full explanation of the relationship between the elastic and geometric load transfer is to much to explain in a forum. I takes scetches and sides of explanations. As allready mentioned, there are books describing the theory but not in a "how to do" manner. I really should try to do so as I am working on an English version of my "Racecar Chassisbook". Okej, I am an amateur writer for amateur racers, but this might have a few things going for it, like a mix of theory and actually building a car. But I will sure not be to sientific exact with my words.

Regards
Goran

[adambrouillard]

Originally Posted by Goran Malmberg

To be correct here I must point out that it is the wheelrate that counts. There is a lever relationship from the spring to the wheel that also include a tilt of the coilover or MCP. That motion ratio is to be squared times the spring ratio. This is becouse we are dealing with both a rise of sprung ratio AND lever ratio. So wheel ratio becomes a lot softer that the spring itself.

The rollbar often has strange shapes with angle arms
making it work partley as a transverse leaf spring and could be hard to calculate accuratley.

Now, add all 4 wheelrates together with the 4 wheelrate for the two sway bars and you have the deflection rate in roll of the car.

As for an theoretical (clean) roll situation, the swaybar could be looked at as four independent torsion bars, one each wheel that is welded solid to the car
in the middle. This is becouse when the bar is twisted the same ammount each side (in different directions) it will remain in rest in its middle. This way of looking at the bar might give an better feel of how it works.

Right, the geometric effect is outside of this equation and is handled separatley.

However, a full explanation of the relationship between the elastic and geometric load transfer is to much to explain in a forum. I takes scetches and sides of explanations. As allready mentioned, there are books describing the theory but not in a "how to do" manner. I really should try to do so as I am working on an English version of my "Racecar Chassisbook". Okej, I am an amateur writer for amateur racers, but this might have a few things going for it, like a mix of theory and actually building a car. But I will sure not be to sientific exact with my words.

Regards
Goran

Yeah, I meant that was the wheelrate not springrate. So then what would be the front eslatic roll resistance? Would it be 900 (both springs and bar once)? Or would it be 1200 because you double the bar because it acts on both sides?

[Goran Malmberg]

The swaybar is a torsion bar and two lever arms. For one wheel you calculate half the distance of the torsion bar together with one arm.
Goran