Good work chaps,
The hand calcs from hanger and gimmo are sound but polar moment of inertia only allows for the torsional stresses, we must consider bending moments across all of the pivot points along the bar and the ultimate equivalent stress created at the min bend (transition) radius as Nigel has suggested.

I have built a 2D model to calculate the maximum permitted stress relative to these moments as well as the equivalent deflections one would expect (based on a non integrated approach, i.e. a rough approximation that will over estimate by approx 10% according to empirical evidence).
As soon as I get some data i can compare materials and dimensions with the predicted deflection for the original bar under identical loads.

If someone can provide the following for the materials of the original bar, eibach and others then i might be able to assist with comparing to the proposed hanger bar:
Youngs modulus for fabrication material
Poisson Ratio for fabrication material
Ultimate Elasticity Stress (can use Ultimate tensile instead)
lengths of levers- Droplink to rear torsion bar
- length of bar including around bends
- Length of rear torsion section
-Length of lever across bar from droplink
- length of lever along arm from drop link
- Min radius of bend at transition point (where lever arm connects to rear torsion section)

The main assumptions in my model are:
symmetry of bar (not a terrible assumption in the coupes case)
The link length between the two sides carries all of the torsional stress (empirical studies have shown this)
The arms of the bar carry all of the bending stress between the drop links and the (again, load cell proven)

Matching the bends of the original is desirable but if there is a way to make it as straight and symmetrical as possible whilst clearing the original parts then that can be shown to be beneficial from a theoretical perspective.


All of this said, I expect Nigels empirical opinion and qualitative understanding on the many set ups he has run could prove to be the most realistic.

Anyway, i'd like to try my best to help if I can.

don't forget that the front ARB uses droplinks and bushed chassis mounts, whereas the rear ARB uses two mounting points on each rear radius arm and therefore no chassis mountings / bushings

I don't know if this makes a difference, but my gut reaction is that it must make some difference in the way the bar behaves and resists torsion

If someone is going to the trouble of making ARBs for the Coupe, surely its a golden opportunity to consider ways to make it adjustable. After all, simply replicating an existing ARB is just adding to the three known manufacturers that already make Coupe ARBs - an adjustable ARB would be unique and potentially very desirable

Having just watched a whiteline you tube video. It seems that an adjustable arb can be achieved by giving a choice of the amount of the end fixing holes as opposed to just one. By moving it back or forward using the different holes it can raise or lower the torsion. https://m.youtube.com/watch?v=QyMgB4v-tZ8&autoplay=1

correct - not exactly rocket science

The problem on the Coupe is that the front ARB has single drop-link mount points on the end of the ARB - not much option for different mount points

Also, on the rear, the ARB is fixed to the rear radius arms, so adjustability would be "challenging"

Can't believe its not possible though

ARBs ready to be shipped

Note:
I understand every doubt, about torsion, rigidity, stiffness etc..
But.. did you evere take on hands, the OEM rear anti roll bar?

It is hollow, and very very light! and full of rust!
I think is not made by incredible material

Ready to be shipped? The research & development stage was fairly rapid then....



I think my point has been missed....

It doesn't matter how thick or light the original Coupe ARB is - its the effect it has on handling.

Unless you have accurately measured the torsional resistance of the original ARB and then produced a new ARB with a known increase in torsional resistance, then you have achieved nothing. Just knowing that the new ARB is "stiffer" is pointless at best and dangerous at worst. Until you have driven a Coupe with a too-stiff rear ARB, you would not believe how dangerous it could be. Think about what lift-off oversteer feels like at 120+ mph - its not fun.

So - a simple question - what changes have been made compared with the original ARBs?

it will need a serious test on track
made by affordables drivers but i guess
there's plenty of room for upgrading the OEM one

Guys, hold your horses. Gimmo is sending his ARBs to hangar for measurements

I spoke to these people about roll bars and they said they would be able to make an adjustable one - Cornering Force - the reasons I didn't proceed was that they had a very long waiting list and the cost for a one-off was high. Once one was made subsequent bars would be able to be much cheaper of course.

Remember that DNA racing in italy can make the bars, but they will cost 180euros + vat each one!
And they want an order for 30 pieces for bar.

Finger cross for hangar work, I can help him sending mine, other I can not do

That makes more sense - apologies for accusing you of jumping the gun....

My arb were shipped to hangar today!

Arb arrived to hangar.
Work can start!

Any news on this or too early to ask for?

hi friends



very sad to comunicate that we have failed !!

I founded the right steel (armonic steel or spring steel); around 1 meter solid bar diameter 22 !

Our machines cant bend such a high resistance steel; I was a bit optimistic because the normal steel was bent without any problem, but this is another story

the following vids show the machine working in "manual" and the second a "auto mode"

in both cases the machine goes in "emergency stop"

https://www.dropbox.com/s/yqrf9i87asycmqk/2016-06-21%2000010.MTS?dl=0

https://www.dropbox.com/s/squssm7crskz0uh/2016-06-23%2000011.MTS?dl=0

I apologize if I have created false expectations

No need to apologize. I still thank you for taking on the challenge

Can't you anneal it before bending, then re temper once you've done the bends?
You're bending the ends of the bar that fit the arms, it's the centre strait part of the bar that acts as the spring so you should be fine.