Ripped from
http://www.gmcmotorsport.co.uk:
"ANTI-ROLL BARS.
As its name suggests an anti-roll bar prevents the car heeling over when under hard cornering. The way it works is to limit the amount the car rolls, by transferring the weight from the outside wheel in a corner, back to the inside wheel, to try to keep the pressure on each tyre as near equal as possible, so we have more balanced car and more stable grip on the road.
The anti-roll bars fitted to Citroen and Peugeot vehicles are like the torsion bars, too weak as standard and definitely need replacement. In fact on some models the lack of a good anti-roll bar system is more important than fitting the stronger torsion bars as a first step to improve the handling, as particularly on AX's they heel over very seriously. The anti-roll bar on all models is in effect another torsion bar linking the centre of the radius arms at their pivot points. As they are mounted in this position they put little or no tension into controlling the movement of wheels over bumps. If you go over a big bump with both wheels at the same time, both torsion bars react but as the wheels have gone up and down together but the anti-roll bar is not actuated, it works to prevent a constant load depressing one side of the suspension.
We can supply a range of up-rated anti-roll bars, for instance, the standard AX GT has an anti-roll bar about as thick as a garden cane, which while better than none at all, is pretty useless. We can supply replacements of varying sizes for Citroen AX/Saxo and Peugeot 106/306/205 from 19mm to 25mm. Note, some low specification models in the AX, Saxo and 106 range do not have any rear anti roll bars fitted and have no fixing s to do so, only fix is to swap the whole rear sub frame/axle assembly from a higher spec model."
Rear Anti-Roll Bar
Citroen AX, Citroen Saxo, Peugeot 106. 18 mm, 20 mm - £60
Link arms for above - £60
Competition units, 21 mm £116 25 mm £215