Coupe Rear ARB options aka FARB on the rear of a coupe

[Rusty]

Anti roll bar / wishbone porn... whatever next!!!

[S2central.net]

There is a danger of pontificating all too long about these things - nout wrong with that as it doesn't hurt, but it can keep you awake at night. Pheck look at the time...

Anyway - having been behind Toms car on a 90 right junction - he was making it very easy to provoke pretty aggressive looking oversteer. For me I think its too lairy - just too stiff at the rear.

I would say Whiteline rear and RS2 front is the best combination... I would change the rear first as that will greatly reduce understeer.

I guess some folk like MarkH have run the whiteline rear for long enough now that they just get used it and forget how soft the original item was... But then MarkH got bored with 400bhp as well after a wee while - heheh.

So my advice - invest in the most adjustable version of the Whiteline rear bar... Get to grips with that, then upgrade to RS2 FARB when funds permit... Keep the S2 front bar if you think there is a danger that the Whiteline needs to be stiffer for you.

Don't forget that a rear LSD (V8 Torsen) might be the added element of driveable oversteer characteristic that is missing from this conversation. Thats the path I am on anyway... Also can't afford to be thinking about whiteline bars right now

Fuggit - I should be in my kip ...

Paul

[VladaS2]

I am also on RS2/Whiteline path. Already got the V8 torsen installed.

So where is the cheapest to get the whiteline?

[rs2coupe]

I am also on RS2/Whiteline path. Already got the V8 torsen installed.

So where is the cheapest to get the whiteline?

try Corey, www.quattronics.co.uk

[Rusty]

Just done a few ball park calculations on the realtive stiffness of the ARB options compared to the standard ARB. These are really simple calculations with plenty of assumptions but are meant to give a rough and ready answer.

Results are:

Stiffness (unitless)

1.0 ...... Std S2
4.4 ...... Whiteline (soft)
4.8 ...... Whiteline (med)
5.3 ...... Whiteline (hard)
15.8 .... Non S2 Coupe Quattro - late type using S2 style drop links.
18.5 .... Std S2 FARB.
21.5 .... RS2 FARB.
21.9 .... Doug's setup

• The calcualtions yielded the simplified force required to produce 1 unit of twist in the bar.
• The ARB was assumed to be a simple l__l shape with a force acting on one end and the other end fully built in.
• Bending of the ARB arms was ignored.
• Pure torsion was assumed.
• Material was assumed constant.
• Diameters were taken from EKTA and here.
• Lengths of arms and distance between DL mounting points was measured from pictures so is open to error (!).

I've gone overboard with this I know but I'm actually quite enjoying it!

Attached is a copy of the Excel spreadsheet.

[Mark Halligan]

Good table!

At least we are back on exploring:

RARB options over and above the normal path of the Whiteline option.

Those figures for Doug's set up would explain the problem with the droplink bracket he had.

I had a look at a pair of blast cleaned rear struts last night and the welding is a little weak, as it is only on one side of the brackets. So if anyone does go the stiffer than Whiteline route, beefing these up could possibly be done by just welding them on both sides.

[4WheelDrifter]

Nice work Andy. Busy at work, eh?

I was pretty disapointed with the RS2/Whiteline combo tbh. Especially after the time/hassle it took to get the Whiteline bar. But I'll wait until I've tried the Bilsteins before I change.
You shouldn't have mentioned those Mark, you're back in my bad books now, for beating me to them.

I just wonder how far you can go with the bar thicknesses front and rear, before you start to muck up the handling.
My S2 certainly rolls a lot more than the A3 does. I get fed up with it being called the barge.

[Rusty]

Had a day of indifference so decided to do some Excel work

These are pretty rough calculations at the moment and really require the correct measurents for each of the options to get improve the accuracy of the arm and bar measurements. Does explain the principle behind Doug's little hiccup!

Thinking of investigating the option of a standard 80 / coupe quattro ARB on the rear. Seems a little less hardcore than the S2 FARB or Doug's setup.

However, Doug wrote that it wasn't a straight swap as there were mounting complications to the rear subframe (over and above reversing the struts!). Checked EKTA and the part number of the FARB on all non uprated or S2 B4s using the S2 style droplinks is the same, so should be rather common. Not sure if that is the same style as Doug used initially but will make sure I get the later spec one. THB, for the cost of a 2nd hand FARB off an 80, quick trip the All Audi should sort that one, I'm willing to give it a bit of thought. I quite fancy sharpening up the handling "a bit"! Might not keep it on there long term but fancy giving something back to the Forum, having extracted sooooooo much .

Cheers for the warning on the struts Mark & Stu. Will have to get them touched up before I do anything long term. Good excuse to get some spares and get them powder coated. Will tie it in with the remainder of the rear suspension/drivetrain overhaul that I'm planning in the near future... IT NEVER ENDS

[4WheelDrifter]

The problem you will find is the older FARBs tend to be attached to the wishbones, so I'm not sure how easy it will be to attach a drop link to them.
Good luck in your search.

[Rusty]

EKTA shows the late Audi 80 & CQ as exactly the same style as the S2 but with a 25mm bar rather than a 26mm S2 bar. I'll have to have a look and see but I'm hoping that reversing the struts will be the only bit of work required.

[Rusty]

Just had confirmation from Alex at All Audi that the later CQs and 80s were fitted with a 25mm item that is identical in fitment to the S2 item. (He's a font of Audi parts based knowledge ). He's going to find me one to play with, have to wait until next weekend for that. Hopefully be able to compare it to a standard S2 FARB, as he's got one of those for his own car!

[Mark Halligan]

He's going to find me one to play with, have to wait until next weekend for that. Hopefully be able to compare it to a standard S2 FARB, as he's got one of those for his own car!

Great, look forwards to hearing what you think following the comparison.

You shouldn't have mentioned those Mark, you're back in my bad books now, for beating me to them.

LOL sorry about that

[Rusty]

Thanks to Alex at All Audi for this, looks like there is also a 22.5mm/23mm version of the FARB that was fitted to early 80 B4s. Having just found it on EKTA, there is also a 24mm version of the FARB listed. These are P/No 893 411 309 E & F respectively and are identical in shape to the S2 FARB. Audi obviously realised that girth was important .

These come out at relative stiffnesses of:

10.4 .... 22.5mm or
11.3 .... 23mm
13.4 .... 24mm

This means that, if all of these are the same size and shape, then there are plenty of options to enable tuning of the car's handling to personal preference. Including the RS2 item and assuming that Ekta isn't lying (!) there are now 5 possible stiffer options to the Whiteline rear bar and all are genuine Audi parts.

22.5mm/23mm (80), 24mm (80), 25mm (CQ, 80), 26mm (S2) & 27mm (RS2.

This gives well defined increases in stiffness to help either dial in understeer for daily driving, or use with the standard S2 FARB and the option to dial in oversteer, even with the RS2 FARB up front (if you can afford a spare one for the rear too!).

Hoping to pick up a 23mm & 25mm item on Friday or Saturday so will know if it fits.

Hope this does fit otherwise it'll be an amusing feckup!

Update Excel spreadsheet attahced.

[Lloyd]

This is a really good thread. Thanks Andy and others for the effort. Does anyone have any experience of the Neuspeed RARB as I am considering fitting this to the RS2, to reduce on-power understeer, and hopefully make the car a bit bit more neutral through the bends....

Any feedback comments appreciated.

[WabTheKing]

i have the struts turned round on the rear with a 7A front anti roll bar there, and a v8 torsen rear diff, i have a little more weight over the back with the radiator which will compensate a bit for any over stiffness of that bar like tom had

cant wait to finnish it, not even been doing this project for a year yet and already seems like a life time!!!

anyone want to sponser a competion car? :mischeif: