Active Roll Control

Citroen Xantia's Activa

Xantia Activa has even more spheres. than a normal Xantia Note the additional sphere incorporated in the front anti-roll bar.

Compared with the XM's Hydractive suspension, Xantia's Activa system has an additional anti-roll function.

Hydractive reduces body roll by stiffening the springs and dampers at the price of ride. If it could stiffen the suspensions to as hard as Formula One racing cars, it would achieve near-zero body roll under hard cornering. However, because we need an acceptable level of ride comfort in a road car, we cannot do that. Therefore Citroen developed the active anti-roll bar, added it to the Hydractive and it becomes the Xantia's Activa system.

Based on the Hydractive, Activa incorporates a gas-filled sphere in the middle of the anti-roll bar. The anti-roll bar is unusually thick at a diameter of 28 mm up front and 25 mm at the rear. The sphere acts as a cushion, thus allows the anti-roll bar to be twisted more easily. Therefore, the 28 mm anti-roll bar performs like a 23 mm one, thus offers less anti-roll function for normal driving.

When the car goes into a corner quickly, a computer detects body roll and close the valves in the sphere. This isolate the gas in the sphere and eliminates the cushioning effect. The anti-roll bar then resumes its original stiffness, acting as a 28 mm anti-roll bar.

If the lateral acceleration is so strong that body roll continues to exceed 0.5 degrees, fluid will then be fed into 2 hydraulic rams at the front and rear which adjust the anti-roll bars pushing the car back to level.

Its claimed, the Xantia Activa rolls at most half a degree. This improves maximum cornering speed. French magazine L'Automobile tested a Xantia Activa on a skidpad and measured 0.94 g lateral acceleration. This compares well with many supercars - The Honda NSX managed 0.93 g, The Ferrari 512TR 0.92 g, Toyota Supra 0.95 g and Ferraris F40 1.01 g. This is even more impressive if you consider the Xantia wears just 205/55R15 tyres ! Most normal cars in its class manage around 0.8 g.