I was thinking today.

On the back of a Fabia an anti roll bar seems to undeniably improve the resistance to roll.

I don't see why though. I Understand the bar fights the "twisting" movement, therefore reducing roll.

What I can't understand is why the movements there to start with? Isn't it a soild rear beam? Does it really have it's "twist" reduced my a little twig of metal?

Edited 25 January, 201115 yr by Rob.

You dont need one, but yes the chasis does flex this much! The stiffer teh bar the more force is applied to outside wheel when turning. Im considering removing my front one on TT to gain better turn in and make the drive more "point and squirt", I should be able to get away with doing this as already have track stiff coilovers KW V2's. It will also reduce some weight off front of car which is always good.

But the rear beam is so much thicker than the anti roll bar everyone fits..

It just seems like the little bar shouldn't help the big thick beam, even if the beam is hollow.

TBH, I'm not sure what i'm arguing here as the proofs in the pudding... it just DOES. The rear beam must be so soft though.

Actually, I've heard stories of it getting bent when used as a jacking point... so I guess it really IS that weak! Couldn't they have made it stronger?

But the rear beam is so much thicker than the anti roll bar everyone fits..

It just seems like the little bar shouldn't help the big thick beam, even if the beam is hollow.

TBH, I'm not sure what i'm arguing here as the proofs in the pudding... it just DOES. The rear beam must be so soft though.

Actually, I've heard stories of it getting bent when used as a jacking point... so I guess it really IS that weak! Couldn't they have made it stronger?

I remember the last time I had the car up on my neighbour's ramp, painting the RARB, and I thought exactly the same thing. How on earth does that narrow piece of steel have such an effect when the rear beam is solid, no joints etc? But like you say, it just does!

The rear beam needs flexibility so that the rear suspension can act independently. It's basically a very cheap and easy implementation of a trailing-arm setup. Making it more solid would adversely affect ride comfort, weight and most importantly, cost. From a manufacturing point of view it would be ridiculous to have different beams for different models of the same car, and if you start with a stiff beam there's no way to un-stiffen it so Grandma has a comfortable soft ride in her entry-level model. Hence the ARB - which incidentally is made of spring steel so behaves very differently to the beam itself - which can easily be bolted on as required.

Its all about the bends, yo!

The ARB isnt mounted in the same way as rear beam tho remember (well I dont think it is) Go have a look. Its mounted onto suspension! I havent had a look at my fabia much yet, my other cars all have teh ARB mounted onto stut (Or coilovers now).

Rear beam reduces flex in the lateral direction (up and down). If looking at rear of car it stops the base or top of suspension arching together, hence one can get a top strut to help the top of the suspension flexing closer together when cornering.

RARB reduces twist force - when one side of suspension raises due to ground or weight distribution it keeps the other side the same spring/unspring length thus making the rear end 'stiffer' and more responsive. It reduces roll essentially, roll is when one side of the car is higher than the other side.

Surprised that few of you guys buy it without knowing how it works. Maybe just me but I HAVE to know exactly how it works before I buy it. :S

Rear beam reduces flex in the lateral direction (up and down). If looking at rear of car it stops the base or top of suspension arching together, hence one can get a top strut to help the top of the suspension flexing closer together when cornering.

RARB reduces twist force - when one side of suspension raises due to ground or weight distribution it keeps the other side the same spring/unspring length thus making the rear end 'stiffer' and more responsive. It reduces roll essentially, roll is when one side of the car is higher than the other side.

Surprised that few of you guys buy it without knowing how it works. Maybe just me but I HAVE to know exactly how it works before I buy it. :S

^^^^^Couldn't have put it better myself^^^^^

OP Rob only has to look under his car and work out which way the forces are reacting on the ARB when cornering. Also Rob, imagine a thicker ARB on your car will twist less and result in flatter cornering but at the expensive of comfort.

Thanks guys, but I do get how it works, and what it does, and why it's a good thing... I was questioning why the rear beam, as it is, twisted at all... but it's just weak and hollow I guess and twists.

The rear beam should not twist, the tyres, springs/dampers take up all the movement. The ARB equalizes the movement on to both sides of the car therefore keeping the car level.

Edited 26 January, 201115 yr by Soot1e

..but surely it is twisting / flexing? As it's a single beam across the back isn't it? If it didn't twist you wouldn't need the rarb? That's kinda what I've been asking...

Rob its a solid beam, however the springs and shocks move. The ARB (I dont know for sure as have a poverty spec sdi without) but mounts to the suspnsion NOT the beam, hence JL's description for you. Im sure you would understand if you spoke to someone in person with your head under the rear of teh car

The beam will flex and twist a little but the aim of the beam is to keep the rear wheels parallel.

Bikerz, you are a bit wrong there, the ARB is clamped around the rear beam and the ends bolted to the bottom of the shocker. You are right about shoving Rob under the car though

Cheers Sootie, as I said only just got my fabia and its a sdi so no ARB for me. Im used to looking at my TT or lupo which have arb mounted to suspension off drop links.

I understand that when cornering, the ARB exhibits a twisting force which in turn lifts up the inside wheel, therefore in turn levelling the car out, (or crudely put, lowering the ride height of the inside wheel, and bring the C.O.G downwards too).

I totally don't understand why fitting a rear ARB equals better front end turn in however. Just can't picture how it

I totally don't understand why fitting a rear ARB equals better front end turn in however. Just can't picture how it

Summery:

When your front tyres breaks traction first = understeer = restrictive turn in.

When your rear tyres breaks traction first = oversteer = turn in increase (because you steer with your front wheel), in exchange for lift-off oversteer.

[Edit: To add, most cars are built with front arb's so it induce understeer (as it is easier to handle when slipping), putting a RARB balances the car to more neutral stance.]

In detail:

The other function of anti-roll bars is to tune the handling balance of a car. Understeer or oversteer behavior can be tuned out by changing the proportion of the total roll stiffness that comes from the front and rear axles. Increasing the proportion of roll stiffness at the front will increase the proportion of the total load transfer that the front axle reacts and decrease the proportion that the rear axle reacts. This will cause the outer front wheel to run at a comparatively higher slip angle, and the outer rear wheel to run at a comparatively lower slip angle, which is an understeer effect. Increasing the proportion of roll stiffness at the rear axle will have the opposite effect and decrease understeer.

http://en.wikipedia.org/wiki/Sway_bar

Edited 26 January, 201115 yr by JLneonhug

Ahhh that makes better sense!

Hence many track boys remove front ARB and drop links (Im going to experiment with TT and do that this season)

I've got H/R roll bars on my golf R32 (+ KW V3 coilovers)

I was running hard front, hard rear on the roll bars.

Changed the front bar to soft, and noticed the steering to be much more darty, but high speed curves, and high speed S-bends are more nervous feeling.

Can't imagine what it would be like without a front ARB, must be scary?

Il let you know soon. I have a mate that removed front one off his TVR and loved the quicker turn in. (And tahts got to be the scariest car to do it to)

cool keep us updated