UrS6 - Anti Roll Bars - Front and Rear - Ideas to make them better

[macspring]

This is a discussion thread so all comments welcome to see how far we can get.

The eleven overarching assumptions are:

1. I've done no research before starting this thread.

2. Because the I5 20vt engine is so far forward in a C4, (and also in a B4), together with the lack of sophisticated / clever differentials due to the C4 chassis and underpinnings being designed so long ago it is prone to understeer.

3. The car is to be used as daily on the road for normal driving, with the odd wet corner being encountered.

4. I have new Bilstein shocks fitted front and rear with H&R springs 29800 and oem bushes. So the car is stiff enough from a leaning point of view in bends, and the changes for the arbs are an attempt to alter the inherent under / oversteer characteristics of the UrS6.

The budget does not stretch as far as changing the centre diff, possibly does to a rear diff, and don't know anything about the front diff. Notwithstanding the money issue, I would still be appreciative if the people who do know about what happens to the handling when you change the various diffs would contribute their comments and experiences for everyone else reading this thread.

5. I'm here to learn.

6. FARB - front anti roll bar.

7. RARB - rear anti roll bar.

8. A thinner farb will reduce understeer.

9. A thicker rarb will increase oversteer.

10. I am conscious that Albert is working on a new bracket and bush arrangement for the farb to move the bar forward to increase castor and in my case stop the outer edge of my tyres rubbing on the wheel arch liners on full lock. Mk1 S8 Avus rims with spacers and 255/35/18.

11. The car we are discussing is a C4 UrS6 saloon, with oem sports suspension from the factory and therefore has a rarb as standard.

So starting with the front:

If I source and fit a farb from a fwd 1.8L four cylinder car will it be thinner than my oem one compared to my oem farb on my UrS6 ? Notwithstanding any changes Albert would need to make to accommodate this mod if it was viable / useful.

If the brackets that hold the farb was made similar to a wheel spacer that alters the PCD as well as the track width, would the fact that the farb bracket and the bar has been moved closer to the ground by say 30mm make any difference to the operation of the farb, assuming nothing else was changed ? Hopefully my question is not muddled ?

Moving onto the rear:

1. If I source two of the thinest oem rarbs available to fit to therear of an UrS6, would they be too much / stiff ? Assuming any clearance and mounting issues are overcome.

2. Is the Apikol rarb just the stiffest oem rarb / similar to the Euro oem sports suspension rarb, or is it stiffer / thicker again ?

3. Is there a bit of a 'ghetto' diy way of making the existing rarb stiffer ?

Welding a bit to it along its length to stiffen it ?
Lengthening where it is mounted at it's end in the wheelarch ?
Shortening where it is mounted at it's end in the wheel arch ?
Changing the length of the drop links ?
Changing the height of the bar as it mounts the two 'inner' mounting points to effect a change ?

I appreciate this thread is long and rambling, but if you can stick with it and people's ideas are thrashed out, something make be 'discovered' which would be a good mod for all C4q owners.

Thanks again for any comments.

[UrS4boy]

Some Front and Rear anti-sway bar comments

This is a discussion thread so all comments welcome to see how far we can get.
8. A thinner farb will reduce understeer.
9. A thicker rarb will increase oversteer.
11. The car we are discussing is a C4 UrS6 saloon, with oem sports suspension from the factory and therefore has a rarb as standard.

Corollaries:

8: A thicker front bar will INCREASE understeer/decrease oversteer (manufacturers like understeer since it is much safer than the alternative WTF!!! oversteer)
9. A thinner (or no) rear bar will decrease oversteer/increase understeer (the safer alternative for the general public)

FRONT BAR

The OE 1BE sport suspension came with a thicker front bar to match the presence and balance of the sport suspension rear bar. There were only two front bars, the 26 mm bar and the 28 mm bar. The sport suspension got the 28, everything else (4, non-AAN 5 and the V6s) got the 26 mm bar. No special 4 cylinder front bar.

All that said, if you wanted less understeer and have a 28 mm dia sport suspension farb, switching to the 26 mm farb could help you.



REAR BAR

There is only one OE rear bar, for the sport suspension. I sold mine but IIRC it was about 17 mm dia. Not very thick but thicker than zero.





The best rear bar for the C4 (IMO) is the adjustable Apikol rear bar. This product has been in development for many years, starting with prototypes and early production models developed by/with/for UrS4guy (Cpt. Hap Maguire) and now several years with Apikol. It does not require the sport suspension rear cross member and has adjustment points so you can dial in the stiffness you want (with in the limited range). It's a done deal, no need to re-invent the wheel. Just pony up and buy it.

http://www.apikol.com/index.php/products/suspension/sway-bars/urs4-s6-rear-sway-bar-kit.html

[macspring]

Thanks Dave.

Does anyone know the dealer price of a 26mm bar - 4A0 411 309 G.

I know about the Apikol, rarb, just wanted to see if there was a cheaper way of upgrading the existing 1BE rarb, rather shelling out for the Apikol one, dearer again when you factor in shipping and taxes to come over here.

[UrS4boy]

Does anyone know the dealer price of a 26mm bar - 4A0 411 309 G.

Available in the US (for example) as the FARB for a 98 C4 Avant (the last C4 built) with the 1BA non-sport suspension.

http://genuineaudiparts.com/parts/in...&siteid=214407

You should be able to find one in the UK at a breakers (I imagine so at least).

I know about the Apikol, rarb, just wanted to see if there was a cheaper way of upgrading the existing 1BE rarb, rather shelling out for the Apikol one, dearer again when you factor in shipping and taxes to come over here.

Admittedly the Apikol bar was developed by Hap Maguire and others (Mike Pederson IIRC) because in the US only the 92 S4s and very early (Aug 92 built) 93 UrS4s. It's main trick is mounting brackets. The other feature that you could attempt to replicate is the adjustment holes at the end of the Apikol bar and the nice Heim-jointed links (those OE links look fragile).

Barring that (pun unintended), having a new, thicker, bar bent to the same configuration as the thinner OE rarb, might be an option. I can't foresee that welding anything onto the OE bar to increase torsional stiffness would work or at least not for very long.

[macspring]

Agreed re breakers yard, but C4 in yards are not as common as they used to be. Also by the time I get one powder coated it may start to add up. Thanks for reply though.

Have to agree re the welding I suppose. As people on here are able to get some surprising things made / re-made, there might be an opportunity to have some thicker rarbs made on this side of the pond ?

Does anyone know of a company that might be interested. A spring company ?

I know the Neuspeed rarb kit makes a good difference on my S2 Avant, even with a front RS2 arb.

Thanks.

[Error404]

ARB tuning is the cheapest way of tweaking the handling, but normally is used to compensate for other short comings / compromises in chassis setup. In an ideal world it would not be required. What you are doing by changing the front or rear ARB independently of the other is altering the relative F/R roll stiffness - this is helping to direct weight transfer and altering the grip balance front to rear or vice versa
If you want a quick fix to reduce under steer, you can reduce the front bar size or increase the rear. A point to note is that overall grip might be reduced in the process. As with all things suspension related, a compromised must be made and there is more than one way to skin a cat
Fundamentally a front heavy 4wd car will always be prone to push on turn-in

[UrS4boy]

In addition to changing front/rear roll stiffness, some tweaking can be done via air pressure, i.e. higher pressures in the front to reduce tire flex and roll-under and lower pressures in the rear. But by lower I mean relative to the front.

For example, if you normally ran 32 psig front and rear, during an autoslalom session (on tarmac) you might go to 42 psig front and 38 rear (just examples from my past)(30 years past).

[Thuppu]

More tyrepressure will reduce grip. I also have been thinking of how to get more grip in front to reduce understeer, and thinking of going with a thinner FARB. The 26mm could be good..? I think this can be a better choise than a stiffer RARB that easily can reduce the grip in rear... well I don't know, just thinking loud here. On the other hand I run a lot stiffer springs than normal lowering kits use.

[JP]

I run a rear apikol and got it on its medium setting. very stiff nice bit of tail out on full throttle round a roundabout. best investment ever. threw my old one away sorry

[macspring]

Hi JP, thanks for your reply, no worries re old one as the saloon already has the factory one.

Looks like I should get the Apikol one and the 26mm farb. Money money.

Accept Alex's comments that a nose heavy car will inherently understeer / push wide under power, just looking to make it less than factory.

Thanks for contributions, they all help flesh out the issue.

[Error404]

Stiffer rear bar is a very good bang for buck improvement

[UrS4boy]

More tyrepressure will reduce grip.

Depends on the tire (tyre) construction (stiff side walls or not? Not = more air makes them stiffer) and tread compound (soft vs hard(er)).

Don't you think handling of this S2 coupe wouldn't have been improved by more air in the tires (tyres)?

[Vorsprung durch Technik]

^^^^^^ I would agree with what Dave said as one or 2 on the Scottish tour recently thought my S6 handled well and i was the only one running 44psi through the 255/40 x 17 tyres.Felt extremely grippy to me and not once did the tyres let go in the pouring rain or in the dry and it was hairy up there.

[Error404]

I think Thomas meant more pressure over & above standard quoted in the post he was replying to

[Vorsprung durch Technik]

Got Ya.