[parapaul]

Bear with me on this - thinking out loud and hoping someone will have some useful input.

• The standard setup is biased towards understeer at the limit.
• Assuming nothing else is unchanged, increasing front ARB stiffness will increase the tendency to understeer.
• Likewise, increasing the rear ARB stiffness will increase the tendency to oversteer.
• Unless buying M3 parts from BMW, pretty much all ARBs come in sets, where both bars are stiffer.

With that in mind (assuming I haven't got it wrong already) what is the benefit in upgrading both ARBs? Assuming the point of upgrading is to dial out the inherent understeer, why change the front one?

Is it just that the upgraded rear ARB is thicker still than the upgraded front, so giving the balance needed? Seems too simple...

[zltm089]

http://www.e90post.com/forums/showthread.php?t=177028

This might help....interesting thread!

[gIzzE]

I would just add an M3 bar to the rear and see how you get on, 22.5mm vs 11mm should be noticeable.

Will the coupe or saloon bar fit a touring?

[parapaul]

Originally Posted by zltm089

http://www.e90post.com/forums/showthread.php?t=177028

This might help....interesting thread!

Very interesting - and also the link within it to the M3 wishbones install thread.

After doing a LOT of reading, it seems the M3 RARB may not be what I want after all, it may make the back end too stiff and instead of the oversteer I'd rather have, it could cause a loss of traction on the inside rear wheel.

What that thread seems to (strongly) suggest is that upgrading the front tension struts and wishbones to the M3 parts will dial out a lot of the inherent understeer - and is definitely a cheaper and easier job than dropping the rear subframe.

I'll have to do that anyway to change the bushes, but I think if I try the M3 front end parts first, at least I'll know whether I want to change the RARB when I do get round to dropping it.

[m1bjr]

ARBs are a SUBTLE mod. More of a 'finetune' to the balance.
There is a degree of truth that you can be too stiff, but depends upon your chosen application and other mods of course.
If you are autocrossing (tight turns) or running tight circuits, then you may find it a hinderance. In the wet traction may be compromised too.
Lifting a wheel on an open diff, or a Quaife results in ZERO traction anyhow. You don't want that.
If you want to make a big change to roll stiffness then just change the springs.
When you get close to where you want to be, tune the ARBs (torsion bars).

The front M3 arms add a degree of camber up front.
So likely that once correctly aligned this will improve mechanical grip in corners - subject to tyre choice.
This will indeed change the balance in the way you seem to want.
Bigger front tyre widths will also do it, but with more grip = more roll= needs more bar!

Its not a simple 'do this and you get this'.
Like all tuning, everything interacts.

More grip to rear (LSD) or better tyres may cause more 'push' or understeer too.

I would try adjusting spring rates first, cheap and easy. Try higher rate to rear, nobody does it as nobody thinks about it.
But 'back in the day' every Escort would run blocks and uprated leafs first.
But you may be pleasantly surprised

[parapaul]

Great answer, as usual. Thanks

[doughboy]

I once talked at length with Kevin Bird while they were developing the B3.5 suspension kit, he was telling me about the findings of the suspension designer/consultant.

He said a common failure of car manufacturers was they used overly stiff springs at the rear to control roll as they didn't want to use stiff ARBs as this would kill the understeer they want, which they see as 'safe'.

A feature of the B3 kit is a SOFTER spring than factory but with stiffer dampers and a stiffer ARB.

The OP is right principal, but its the tested pairing of ARBs thats important, the ratio of stiffness between front and rear, so just guessing will probably go wrong.

I have the Hartge ARBS, which is a larger front and MUCH larger rear.