6 replies to this topic

[RoutariEnjinu]

Hello people that blend racing and mathematics. I'm not particularly good at either.

 

I've heard that the lever arm part of an anti roll bar (sway bar), that the drop links connect to, should sit horizontally, assuming good clearance etc.

 

What would be the effect on the behaviour of roll, if that part was angled either up or down?

 

For a given deflection of the suspension arm it connects to, would the spring be loaded a different amount?

 

Would it be possible, on a standard anti roll bar setup, to adjust the angle of the bar itself, using adjustable drop links, to adjust the roll coupling of both axles a small amount?

 

I know the correct usage of adjustable drop links are used to ensure the anti roll bar doesn't foul any suspension components after lowering, or sometimes to bias the loading on the tyres in drag racing, and sometimes even to pre-load the anti roll bar in oval racing. I also know the correct way to adjust roll coupling is to change the diameter of the bars themselves, or adjust how far along the lever arm part of the bar the drop links connect to, which incidentally, adjustable length drop links would work well for.

 

So on a standard setup, would having the anti roll bar angles different, front to rear, affect the roll coupling of the car? Would it be minimal? Would it do so in an undesirable way?

 

Thanks.

Edited by RoutariEnjinu, 15 October 2014 - 14:50.

[RoutariEnjinu]

It's a weird one to get my head around.

So if I set the rear with the ARB blades as close to parrallel with the arm it connects to as possible during its resting state, and with the front, set them at different angles, would that be a poor man's way of making the rear ARB relatively stiffer than it was, compared to the front with the stock setup?

It seems to make sense if parrallel means more loading for a given deflection.
But then it also seems like running it at a bigger angle would be like having a shorter blade?

I suck at geometry, sorry.

[RoutariEnjinu]

I also guess that if it isn't parrallel, the response wouldn't be linear?

Again, I suck at geometry. I can't find my old K'NEX set!

[DaveW]

Forgive me, but there is, possibly, another deflecting force at play when the drop links are angled.  The bar can deflect in torsion (in the obvious way), but can also deflect in bending.  This can reduce the overall stiffness, sometimes dramatically, and can even cause the bar to fail in bending.  One manufacturer is (in)famous at neglecting this freedom, sometimes with dire results....

[RoutariEnjinu]

In parting, any possible effect of the relative change of position between the two ends of the droop link, will be "more pronouced" with a short droop link [larger angluar change],

 

Having a hard time replicating this in Algodoo 

 

The mounting points are in the same place for both. The only variables I'm changing are the initial angle of the ARB lever, and the connecting drop link length to compensate for that angle change.

 

The angles moved through, by both the ARB lever in its mounting point, and the lower arm in it's mounting pojnt, seem to always be the same, either that or small enough to be difficult to measure.

 

I don't venture into this forum often for a reason, so sorry if I'm being stupid. 

 

I think the maths involved is here, but it's all foreign to me 

 

 

Common sense tells me that if the crank was rotating at a fixed rate, the piston would accelerate away from TDC, and decelerate towards BDC, meaning at 45 degrees, a given unit of piston displacement means more of an angle change on the crank, compared to at 90 degrees.

 

With the ARB levers sitting perpendicular to the arm they're linked to, then any movement would progressively load up the spring in increasing amounts. Out of angle, it would start initially with more resistance, and then ease off as it got closer to perpendicular?

 

I wish I had a math lobe in my brain.

Edited by RoutariEnjinu, 16 October 2014 - 14:17.

[desmo]

Geometric changes will affect the rates of movement between the two linked parts. When a lever is pivoting at one end and linked at the other the motion rate will either rise or fall depending on the fixed geometry. Forgive me if this is either trivially obvious or poorly described.

[Greg Locock]

Not too sure if this has been mentioned, but as you depart from the orthogonal setup then ride height will affect your arb contribution to roll stiffness.