Advice On Rear Arb Size/thickness

[SweetBadger 94]

Hi all, after a bit of advice on what size arb to go for on the new race car. We're currently running the following spring rates/tb's :

 

6inch 400lb springs up front

standard front arb

25mm t/bs rear

standard 19mm arb, plus 20mm Whiteline ARB (connected to stub axles via rose-joints)

 

With the Whiteline ARB on it's maximum setting the car handled quite well at our last race at Cadwell, but I think that the 27mm arb we had in the old beam gave a sharper turn in / less under-steer.

 

I want to keep the Whiteline ARB so that we can adjust for different conditions (i.e. soften it off in the wet), but think a thicker fixed ARB is in order.

 

1. Anyone have any idea what the whiteline ARB is equivalent to on its own? This thread gives the equivalent of 22-25 mm in conjunction with std arb http://forum.205gtidrivers.com/index.php?showtopic=69138 . So that's effectively +3mm on soft to +6mm on hard.

 

 

2. Any suggestion on what ARB to go for to use in combination with the Whiteline to work with the 25mm tb's? I'd say we'd probably want the equivalent of a 28mm arb on the hardest setting.

 

I was thinking 23mm or 24mm - Then we'd have the option of totally disconnecting the Whiteline in very wet/slippery conditions, plus the soft, medium and hard settings.

 

Thanks.

[j_turnell 136 3 Cars]

A 23-24mm would be a cheap option as you could use a xsara vts/gti-6 bar and cut it down and weld or get it resplined as I did. May be worth trying this before spending out on a 27-28mm bar. My setup is a fair bit different to yours being a road car but i run the 309 front and 24mm rear and turn in is nice and sharp.

[SweetBadger 94]

I have been on the look out for a xsara vts / gti6 bar or the 106gti / saxo bar which I've read is a direct fit with 306 end plates (with a spacer as it's a little shorter). I don't have much time at the mo to sort out getting a bar modified so I've just ordered a 24mm bar from Torsion Performance.

 

Will see how we get on and report back. Worst case I'll just sell the 24mm arb and Whiteline arb then put a 28mm one and be done with it!

[jord294 91]

I know you can get up to 28mm retaining 205/309 arb levers

[Miles 331 1 Cars]

If going larger than the std bar then it is a very good idea to use the 306 end plates, less wind up on the tapper part then, but then your limited on using performance torsion which I have never liked along with quite a few others

Edited June 13, 2016 by Miles

[camgti 56]

May sound like a silly question. What are you currently struggling with and why do you want to change it?

 

Cam

[SweetBadger 94]

We're not struggling as such, just in comparison to last years car this one seems a bit more prone to understeer and not as sharp on turn-in.

 

The suspension set-up is exactly the same apart from the rear-arb. Last year's car had a 27mm arb, new car has a std 19mm arb plus a Whiteline adjustable arb (on it's stiffest setting).

 

I don't think the std arb plus the adjustable one is as stiff as the 27mm arb from last year, so I want to increase the rear roll-stiffness (to hopefully reduce the tendency to understeer). The easy thing to replicate last year's set-up would just be to fit a 27/28mm arb and remove the whiteline arb altogether, but I want to retain the adjustment that the whiteline arb provides.

 

Admittedly I'm not quite comparing apples to apples as we have more power than last year and a heavier git6 lump up front instead of the MI, but I think a stiffer rear arb will improve things. It's just not easy to gauge how much additional roll stiffness the whiteline arb gives, and therefore difficult to decide on how much to increase the standard arb by!

[camgti 56]

Most of it is down to the ARB. Whack the 27mm bar back in there. Im skeptical with thise whiteline bars.

[SweetBadger 94]

Not an option I'm afraid - it snapped in the crash at Oulton at the end of last season!

 

I used to run a whiteline bar with a standard rear beam in my old 205 back when it was for road use / occasional track days and on the medium setting it made a quite noticeable difference (improvement in most conditions but could be a bit skittish over bumpy ground or slippery conditions), so they do work. It would have been too stiff on the hardest setting with standard torsion bars / dampers.

 

I suppose I could figure it out by measuring the amount of force required to move the suspension with the bar on different settings (jack on a set of scales under the suspension arm), but I have the 24mm bar with me now so will give it a go - if it works next weekend at Snetterton I'll report back, otherwise look out for the for sale threads!

Edited June 17, 2016 by SweetBadger

[SweetBadger 94]

Well, I can now say from experience that the 24mm arb in combination with the Whiteline bar is very effective! With the Whiteline bar on the middle setting the car had a neutral - oversteer feel to it, much better on Coram - the long sweeping corner before the start finish straight (less understeer and allowed me to steer it on the throttle).

 

I can only compare with last years car that had the 27mm arb, but I'd say the combination is stiffer than the single 27mm bar, so result!