17mm Anti Roll Bar spec? Wheel rates?

[MrDangerUS]

Does anyone know what is the torsional stifness of Esprit 17mm ARB?

 

Also, I'd like to find out 88/89 wheel rates.

 

Thanks!

Edited November 8, 2013 by MrDangerUS

[Bibs]

Without wishing to sound flippant, why do you want to know this?

[rogerch]

I'd like to know the torsional stiffness of the ARB, because if I ever decide to to further increase the roll resistance at the front, I need to know my base level which would be the stock part.

I suspect that changing the mounts, on advice from the factory, reduced the front end roll enough for road use, but torsional stiffens of the stock product is still good information.

[Vulcan Grey]

The stiffness is directly proportional to the diameter... So if you know you have a 17mm, then there is no need to know the stiffness.  Just tell the anti roll bar manufacturer that you have a 17mm bar and want something x% stiffer...

 

The 17.5mm bar is the stiffest that Lotus used as far as I know, It was on the X180-R and maybe the Sport 300, not sure.  The SE and the Sport 350 both had 17mm IIRC...

[rogerch]

I did not know that. It's good information, but I feel sure he would need to know measurements, straight length, bend angle, from the bend to mount eye etc.

And I seem to recall from a distant past that a tubular bar gave stiffer ratings, and that wall thickness also had a bearing on it.

[Bibs]

No, they used bushes, not bearings.

[Vulcan Grey]

A tube is stiffer in general, unless you made it a tiny tube for some reason

 

So then the calculation for stiffness would be different to go from a 17mm solid bar to an xmm O.D. and ymm I.D. tubular bar to achieve z% greater stiffness...

 

The anti roll bar is just in torsion in the portion that goes across the car, the ends don't have anything to do with it, unless you change the mounting points.

 

And yes to have a random manufacturer make a new stiffer bar you would have to supply them the dimensions to fit the car, or a bar for them to copy.

[sailorbob]

For the same diameter a bar is stiffer than a tube. The calculation for the torsional stiffness is:

 

J = Pi D^4/32

[rogerch]

Now thinking about all this again, I seem to recall you could change the torsional stiffness with heat treatment to the same bar.

Just to complicate the equation.

[sailorbob]

Yes, I was oversimplifying it as you usually are just comparing like for like materials of the same length when comparing anti-roll bars of different thicknesses and this formula is sufficient for doing that. The "J" in the formula is actually the torsion constant and this along with the material's characteristics and length is used to calculate the bar's torsional stiffness.