Uprated rear anti-roll bar - Peugeot 205 GTi

[benlilly]

Hi all,

I have the oportunity to purchase an overhauled rear beam for my car with an uprated anti-roll bar. It has also been lowered by 30mm.

I'm not too clued up on suspension and was wondering how this might change my cars (Peugeot 205 GTi) handling.

I understand changes at the rear should be matched at the front to keep the handling fairly neutral and that increase in stiffness at the front will lead to understeer and an increase in stiffness at the back will lead to oversteer.

The car is fitted with a Quaife limited slip differential.

Thanks,

Ben

[Os7213]

Hi

I cannot say I know everything on suspensions but I have modified by myself and that work good...
Unfortunatly I dont know Europeen models like a Peugeot 205...My knowledge stop to my particular application.

For your question If you have adjustable front shocks you can increase bounce a little to compensate.
The best is to know the diameter and material of the front and rear bar

Also here an example of my rear supension setup where you can see the rear swar bar bracket:




Sorry for the picture not really clear but is to show how you can do "any" required setup
I have found 2 solutions if you have this type of rear brackets, change bushings type to made the bar react differently and changing the height of the bar by adding spacers and different bushings sizes.

Just for fun I would try leave the upgraded rear bar to its orginal position and test just to see if this can compensate for the understeer caused by 2 ways lsd assuming this is a 2ways.

Hope that help
Hugo

[benlilly]

Hi Hugo,

For your question If you have adjustable front shocks you can increase bounce a little to compensate.
The best is to know the diameter and material of the front and rear bar

I don't have adjustable front shocks but can easily add an uprated anti-roll bar from the next model up (309) to try and balance things or use uprated shocks. My budget does not stretch to fully adjustables.

I have found 2 solutions if you have this type of rear brackets, change bushings type to made the bar react differently and changing the height of the bar by adding spacers and different bushings sizes.

So the operation of the ARB is varied by changing the amount of friction on the bar and how much 'pre-load' it is under (can't think of a better description)?

Just for fun I would try leave the upgraded rear bar to its orginal position and test just to see if this can compensate for the understeer caused by 2 ways lsd assuming this is a 2ways.

I was thinking the limited slip differential would reduce understeer. It is a Quaife (automatic torque biasing type).

Thanks,

Ben

[TR-Spider]

Hi Hugo

Generally a anti-roll-bar reduces the amount of traction on the mounted axle, i.e. front anti-roll-bar increases understeer and rear anti-roll-bar increases oversteer.

You mount the anti-roll-bar to reduce the body roll of your car and thus increase the sharpness of the cars response to driver input, which will be most noticable in s-bend curves: if the car rolls less, than you have to wait less for the car to settle into the roll and thus you can apply the direction change faster.

What Ben probably means with the bushing type is the way you connect the cars body with the anti-roll-bar: the bushing itself will deform more or less and thus the load is transferred faster or slower.
Example: if you use a soft rubber bushing, first the bushing gets squeezed and then the anti-roll-bar starts taking load. On the other hand if you use a hard, solid bushing the anti-roll-bar will immedeately take the load and transfer it to the wheels.

An LSD typically increases the tendency for the axle to run wide (i.e. oversteer at the rear and understeer at the front) BUT it makes things MUCH more predictable. Without LSD, wheel with less grip (inside in corners) gets more torque and thus starts to spin, which does upset the cars balance suddenly. That indeed can cause sudden understeer, so I assume one could say that the LSD somehow reduces understeer. With LSD (especially Quaife=Torsen type) the torque gets transferred to the wheel which can transfer it to the road, so you avoid the spinning wheel and the sudden loadchange. Thus you can get more torque on the road and effectevely go faster. However, I personally haven't driven it on a frontwheeldrive car.

So it is up to you to test...your idea to counterbalance the eventual oversteer with the thicker front bar is very good.
I would advice you just to change one thing at the time (rear bar, frontbar, lowering), otherwise you will not be able to evaluate the impact of the change.

Ben, just of curiosity, what is that car on your picture?

Thomas

[benlilly]

Hi Thomas,

I think you may have Hugo and myself mixed up but thank you very much for your input.

Ben

[Os7213]

Hi guys the car in picture is a Toyota Trueno Ae86 1987 hatcback

And yes Thomas you are right this is a good explanation about changing bushings types.

Also for lsd I will explain why I think it give understeer.
Like you said on open diffential type the inside wheel have less grip, so it "help" the car to turn since the exterior wheel get more power that the interior one.
With lsd the 2 wheels got the same load of torque so on a rear wheels drive car it will "push" the car to the exterior of the curve.
However this can be now controlled with the throttle.
So for me an lsd can decrease understeer but with throttle fully open to cause wheels spin.

You're totally right about it make the car rellay more predictable tho!

Hope that help
Hugo