New anti roll bar upgrades???

[Rusty]

I covered all this in my original FARB on the rear thread. Torsional stiffness is ralated to second polar moment of area (I) and thus for comparison the term of interest is Diameter, d^4 assuming that they're solid and the same material. The shorter arms then reduce the levereage and so make the overall system stiffer.

In this manner you can compare the S2 and RS2 bars, the d,S2 = 26mm, d,RS2 = 28mm.

26^4 = 4.57x10^5 mm^4

28^4 = 6.15x10^5 mm^4

Thus the RS2 bar is 1.34 times stiffer than the RS2 item.

In the case of the rear bar the OE item is approx. 12mm (from memory, better check...) and my FARB is 25mm, however, the levers on the FARB are 1.5 times longer so:-

d,FARB/d,OE = 25/12 = approx. 2

so (d,FARB/d,S2)^4 gives 2^4 = 16.

Divide this by the arm ratio of 1.5 and you get approximately 10 times stiffer :-)

For a RARB of the same design to be 10 times stiffer the diameter would have to be the 4th route of 10 times larger, thus 10^0.25 = 1.77 times.

12mm x 1.77 = 21mm approx.

I've lost my data, will have to measure the RARB I've got in the garage and the FARB in the cupboard at my flat.

[stevieyid]

Andy thats impressive mate. Using your calculations what thickness should the new anti roll bars be for the front and rear?

[stiglet]

Andy, assuming it's all the same material and thickness then yes. I doubt thats the case with the Whiteline though.

[Rusty]

These are assumptions and so the errors are pretty large. There are a lot of other factors that affect things but to get an idea of how a different design bar will relate to my setup (and again, for Error's setup this will differ again). As for the whiteline, we're not worried about exact numbers, something withing 20% is fine by me.

As I've already said, the 26/25 setup on mine is a bit much for track work but great for normal driving. I seem to remember that even the OE RARB can cause lift-off oversteer issues (ask Fatty about the ADI-06 parade lap ) so the Whiteline doing the same indicates that this is more of a geometry problem.

I think that it would be worth making this bar stiffer than Whiteline, there is no point producing the same product for the same price If we take the 24mm FARB as the max criteria and the Whiteline stiffest as min then you'll have a product that is idael for use with both S2 and RS2 front bars IMO.

Based on the rough calcs above, the 24mm FARB will translate to approx 20mm diameter in a stock design RARB. The whiteline is 16mm(?) and there is limited space for lengthening the arms. The whiteline holes are around 40mm apart with the centre something like 350mm away. This gives lengths of 310/350/390 or an adjustment of just over 10% from the mid point.

Thus, taking 18mm and 19mm bars (and assuminig 1001 other things ) and having a range of settings, you should get something prretty good.

(16^4/12^4) = 1.33^4 = 3.1 times stiffer than OE, thus 2.8/3.1/3.3

(18^4/12^4) = 1.5^4 = 5 thus 4.5/5/5.5

(19^4/12^4) = 1.58^4 = 6.3 thus 5.7/6.3/6.9

(20^4/12^4) = 1.67^4 = 7.7 thus 7.0/7.7/8.4

(21^4/12^4) = 1.75^4 = 9.4 thus 8.5/9.4/10.3

Gut feel on this one is that a 19mm or 20mm bar will give the best range of adjustment for most people. I love the 10x stiffer bar or road use but that'll be a bit much for most. Combined with a 28mm FARB this will make a much more aggressive setup for all drivers.

[newsh]

Pete Berry asked me to add his comment that he believes there's no point in going stiffer than the RS2 FARB.

Also Andy I've been running my Whiteline at min

[Rusty]

My point was that the whiteline exists and the new rear bar is proposed as being the same price so it seemed silly to make the same thing for the same price...

[newsh]

My point was that the whiteline exists and the new rear bar is proposed as being the same price so it seemed silly to make the same thing for the same price...

Except it doesnt have to come from Oz But actually I agree, a little stiffer wouldnt go amiss. I keep meaning to try mine back on stiff again.

[ESPengineering]

Hello lads,

Steve dropped the roll bars of earlier on today and nothing looks to painfull, I really dont know why they bothered putting one on the back it looks like a Mcdonalds straw.

All that maths is far to complicated for me I'll get my hammer out and hit it untill its about right lol.

All joking aside the calculations are good but there are to many variables to consider, i.e material spec heat treatment loading on the car it's self. I've no way of knowing, without great expense, what the grade of material is on the stock bars so we really do have to see how we get on.

I've got the material prices back now so I'm going to start putting the provisional prices together this week I can then get you some ball park figures. I'm pretty confident that I can comfortably beat those other prices and even more so if we get a good group buy together after we've got the testing done.

Will keep you posted

Liam

[k.alle]

Seems like a really good project this!
I'm very interested in a RARB..

But I have to agree with Andy_Casey on this one, the only logical would be to make a RARB that is stiffer than the Whiteline at it's stiffest setting.
Just seems a bit weird to invent the wheel twice?
Plus it would be nice to have some more aftermarket choices on the RARB as there is only Whiteline ATM that I know of.

Just my 2 cents..

[Rusty]

You need to take the experiences of various members on here, me included, to get the best starting point. The maths is just to compare the options and narrow one of the variables, it gives a ballpark idea of how each will perform relative to others' experiences, I'm trying to relate the difference in bar style to my setup as that's as mad as you want whereas the Whiteline is a bit tame for some...

What differences in terms of torsional stiffness does heat treatment make?

If you make a pattern then can you make any diameter bar? Are these to be machine made? If it's a CNC machine then that'll make things easier...

[anton]

heat treatment can make a huge difference, i think its worth making the rear bar have different settings to the whiteline bar, but poosibly not carrying on from the white line, as in have an overlap perhaps? i am personally looking forward to the front bar as it is the only think not really available at present.

Ant

[Error404]

Good work Steve

[stevieyid]

Well look like this thead is getting quite a bit of interest so once they are made up im sure a group buy would be a good idea. Im off the same opinion the rear bar should be thicker than the whiteline and probably make the front the same as the rs2 bar. Hopefully we will get good results from this.
@Liam thanks for taking this on. Love that jag caliper project

[stevieyid]

Just a little update on these. Liam emailed me the other day. He just working on the fixings, once they are done the prototype will be done. Hopefully be then ill have my S2 sorted and he can fit them and see how we go. Not sure on pricing etc but im sure Liam will let me know in the next few days.

[sjw185]

Just a little update on these. Liam emailed me the other day. He just working on the fixings, once they are done the prototype will be done. Hopefully be then ill have my S2 sorted and he can fit them and see how we go. Not sure on pricing etc but im sure Liam will let me know in the next few days.

Steve any update on these? was looking to get a rarb soon.

cheers