front and rear ARB

hi friends

does anyone have some drawings of the front (strut brace) and rear ARB

I have at work several tube bending machines and I was thinking if I can produce them by myself

any help will be appreciated

the message is also for users that have already installed these two bars: it's enough to take diameter thickness metre and goniometer !!

maybe this can be interesting for others people here...

ciao

Good idea! I will definitely be interested in buying an uprated rear ARB.

i would buy a rear ARB hanger, if you could beat the price of a whiteline or eibach

It isn't simply a case of replicating the diameter of the tubing and the angles of the bends - you would need to know the exact material, the wall thickness, torsional rigidity, etc

It would be entirely possible to make an ARB that is stiffer, without actually increasing the thickness of the bar. Similarly, it would be possible to make a bar that is thicker, but which is actually less resistant to roll than a standard ARB

Not as easy as it would first appear....

I think it's not so difficult, material will be the cheaper of the market probably Fe360 sure at 99%

remember that resistance to torsion module not depends on type of steel

of course I will need to make some tests with different thickness

dont think that suppliers of these bars are NASA enginners...

for the beginning I need to know external diameter thickness and bends and after I will try to prepare a prototype

https://www.youtube.com/watch?v=cjdOSQ4lbaU

in the video the diameter 22x1,2 but the machine can bend up to diameter 30x2

You're talking about bending bars, not tube?

bending tubes with important thickness 4 5 6 mm

the inner section of a bar give very little help in torsional rigidity so why to use a bar that only increase weight and give little more that a tube?

Fair comment, if it works, it works

Hanger seems ontop of it.
Richter and witter(of bilstein fame) wrote a good design article in 2010 on ARBs, rolled pipe and solid bar. The calcs are fairly simple as long as it is kept as straight as possible. We could do them in 2D (Non FEA) and probaly prove the spring travel under equivalent loads to be within a certain error range for a variety of configurations/materials.

just let me have something to work on it ....

Do it, hangar. I am tired of searching for an uprated bar.

+1

need some sketches.....

As a suggestion why not buy a second hand set from a standard 20vt and work from there.

Hello hangar!

I can ship to you

- UPRATED FRONT BAR (Eibach)
- standard rear bar

To replicate them
Consider that Eibach bar are solid, I think.
You can take measure of the front, calculate volume, and knowing material obtain the answer: hollow or solid tube?

Let me know if you want the bars shipped!

I'm 100% sure that I cant bend solid bars

all others operations are not a problem

Gimmo what means "I think" if you have please check it

so if I read correct: you can borrow your bars and pay only delivery costs to send and send back to you??

from my calculations:

Ø22 solid is has a bending modulus of 1045 mm3

maximum bending capacity of my strongest machine (Ø30x2) 1155 mm3

so we are in range for bends with medium radius greater 1,5 times diameter (22*1,5 = rm 33 mm)

about the strenght of the rear arb we are going to design and build:

solid Ø22 has a torsional strenght of 2090 mm3

a tube Ø22 and 6 mm ticknes has a torsional strenght of 1893 mm3

so only 9,5 % less than solid Ø22

with tickness 7 we have only 5 % less

Gimmo you are very fresh of study ... is all correct ??

Hi Hanger,

Excellent work with the calcs. Are you able to calculate the torsional strength of the standard rear ARB? Best to be sure that anything you design will be an improvement over original equipment.

hi Gunzi

we are to design at rigidity and not at resistance

this is the formula:



where (fi) is the angle of torsion in radiants (1 radiant is around 57°)

Mt is the torque in Nm
l is the lenght of the bar
G is the shear modulus (for the steel is around 81000 N/mm2)
De is external diameter
Di is internal diameter

for the solid bar is enough to put Di=0

remember also that we are in SI (international system of units) and for the formula you have to use Newton meters and the angles are in radiants

if we design Øe 22 mm and Øi 8 mm we will have a very small difference in the angle of torsion (fi) but of course always greater than a solid Ø22

the Eibach arb are too expensive, my bars can be easily under 70 € each

I confirm, but I made calculations taking into account Polar Moment of Inertia of the tubes.

Remanimng
J = Polar Moment of Inertia
Js = J solid tube
Jh = J hollow tube

Dext = external diameter
Dint = internal diameter (equal to Dext - 2*thickness)
pi = 3.1416

solid tube
Js = pi * Dext^4 / 32

Hollow tube
Jh = pi * (Dext^4 - Dint^4) / 32


_ Eibach REAR arb is 23mm, solid tube -> Js_eibach === Js_23 = 27'437 mm4
Whiteline REAR arb is 22mm, solid tube -> Js_whiteline = Js_22 = 22'998 mm4


In case of hollow tube, with thickness equal to 6mm:
Dext = 23mm, Dint = 11mm, hollow tube -> Jh_23 = 26'036 mm4
Dext = 22mm, Dint = 10mm, hollow tube -> Jh_23 = 22'016 mm4


Now we can compare solid vs hollow, eibach vs whiteline vs Hangar

__ Eibach: 23mm, solid --> Js_23 = 27'437 mm4
_ Hangar: 23mm, hollow -> Jh_23 = 26'036 mm4
Less than 5% of difference


Whiteline: 22mm, solid ---> Js_22 = 22'998 mm4
_ Hangar: 22mm, hollow -> Jh_23 = 22'016 mm4
Less than 5% of difference


For material: DNA racing is the only one that declare the material for their bar, http://www.dna-racing.it/#!componenti-grande-punto/c1dnr

It if Fe36

Fe36....

is the most common cheap and used steel...

Gimmo do you want to proceed with delivery?

No problem, the only problem is time
I can prepare all on saturday morning, but I am not sure that I can ship them on saturday, maybe next week

Otherwise, I can take measureas, but I it will be the first attempt for me, so I think that shipping is the best solution

I also prefer shipping because I will realize a control desk with the originals so every new part that will be produced has to fit into the "mask"

send me PM when ready

Good!
And let's make the ARB for our cars!!

How are you dealing with the method of bending?

All the Coupe ARBs I have seen are not crush-bent - there is no reduction in diameter on any of the bends.

I have looked at the Mecart tube bending website and it looks like the bends are crush-bent. Your comment that you can't bend solid bar would suggest you can only crush-bend.

Surely this will alter the torsional rigidity of the ARB if the cross-sectional area is reduced

Also - I understand the very minimal difference between solid bar and tube, but you mention 22mm external diameter and 10mm internal diameter - is this tube readily available with such a large wall thickness? I would have thought that solid would be significantly cheaper.

Finally - whilst I applaud the very good intentions behind the thinking on this thread, I have to express a degree of concern. A Coupe with an incorrect ARB is a nightmare to drive. I once had a Whiteline 24mm rear ARB and the car felt like an old-school TVR on ice - it over-steered everywhere. Guessing at dimensions and material can only lead to inaccuracies in the torsional resistance offered by the ARB.

I acknowledge your knowledge of materials is far greater than mine, but is it really true that different grades of steel have the same torsion characteristics? I would have thought a high-carbon spring steel would be very different from cheap mild steel

Lifted from a discussion on ARBs on another forum:-



So - have you considered the elastic limits of Coupe ARBs? What is the maximum possible wheel deflection across an axle? Does this exceed the elasticity limit of a low-grade material such as FE36?

I wouldn't be bothered if you were making alloy light rings or powder-coated slam panels, but the consequences of a design error on an ARB is that someone ends up on their roof in a field

Dear Nigel

thanks for all your sharebles worries..

In Mecart we have 2 kind of bends:

bend for flexion (on small light tubes)
bend for stretching (on big tubes)

this are the only 2 way to bend tubes with actual industrial tecnologies

of course in every kind of bends you have to exceed the elasticity limit so you have to unnerve a every time the material to keep the new geometry

of course 1,5*diameter for the bending radius is a good compromise to not unnerve a lot the external fibers of the steel

I cant bend solid Ø22 only because I think it exceed the machine capacity and I'm afraid to break something

I agree with you that the results can be different and in some cases it may take to terrible mistakes but we are here with good intention we dont want to force no one to use my arb I will test first and if required I will apply changes to design until I will reach a acceptable result.

a better steel will have, true, more resitance at higher torque but the same rigidity of a normal steel

I think we are losing a little in translation here, but as I know no Italian at all, we have to work with each other...

I understand that elasticity limits need to be exceeded to form a bend, but the article I quoted was pointing out that elasticity limits can be exceeded when the ARB is actually fitted to the car if the suspension travel is sufficient (or if the material is sub-standard)

Quite simply, on some cars, the twisting of the ARB in normal use could cause the ARB to remain deformed. Repeated application of the torsion force will cause the ARB to fail (with the obvious potential consequences)

I note your point about the optimal bend radius being 1.5 * diameter - I think you may need to look closely at the rear ARB - from memory, there are a couple of quit tight bends

What about mandrel-bends? - this would retain the external diameter throughout the bend and therefore would not reduce the torsional rigidity

Nigel, do you know the material of Eibach or Whiteline bar?
The only info I found was on DNA site: Fe36

Mr. Nigel

true, some technical term are very difficult to translate

when you exceed the elasticity limit with to reach breaking limit you modify the mechanical behavior of the steel (see the graph I posted); after this you have a more wide area of elasticity (a higher limit of elasticity) a more narrow area of enervation (really dont know how to translate sorry !!)

the torsional stress you are talking about that make ARB remain deformed is a wrong design problem; the torque on the ARB has to never execeed the new elasticity limit after the mechanical yield of the bends

if exceed this limit it will take to a sure break; the same happens with a normal steel wire if you insist with heavy bending on one side and to the opposite you will break wire after few cycles

about mandrel-bends I think it's a kind of bend for flexion

it will be more easy to do than to explain

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.