GIANT TEST:

Citroën Xantia Activa
Audi A4 1.8T
BMW 320i

The Activa has all the hallmarks of a winner: great looks, excellent packaging and, of course, gas-oil suspension. Not just Hydractive 2, but a wholly logical development of the arrangement that serves ordinary Xantias so well. The Activa is the world's first production car to get roll-controlled suspension - not quite 'no roll' but something very close. How does it work? Under normal conditions, the Activa's two anti-sway bars, connected to the suspension arms via a gas-filled sphere, run soft, benefiting ride comfort. On the turn, they switch to firm, effectively doubling in stiffness as the cushioning gas sphere is isolated. That's phase one of the active roll control system, or ARCS. In phase two, which operates under sustained cornering, two hydraulic rams, one at each end and on opposite sides, act on the anti-roll bars, resisting lean. Pressure to the rams is controlled by a roll corrector (similar to that used to set the Citroëns ride height) which prevents tilt of more than half a degree. The whole operation, detection by sensors and computer-controlled correction, is blink-of-the-eye quick. Corner over, the corrector returns the rams and anti-roll bars to their normal straight-line setting. All this wonderful hydro-pneumatic trickery, unique to Citroën, makes the metal-sprung suspensions of the Audi and BMW seem positively primitive. Of course, they're not. At the front of the Audi there's a complex arrangement of aluminium links and knuckles, designed to optimise camber, toe-in and compliance. It's not computer-controlled, but it couldn't have been designed without the aid of a computer. Ditto the multi-link rear end of the BMW, which does a wonderful job of gluing the tail to terra firma. BMW describes the 320i's 50/50 weight distribution as 'perfect', implying that its front-drive rivals are excessively nose-heavy.

To do justice to such an advanced chassis, the Citroën Xantia Activa also gets the XM's single-cam eight-valve turbocharged 2.0-litre engine, yielding, like the Audi and BMW, the 150bhp - a modest 15bhp increase on that of the Xantia 2.0i 16V twin-cam. However, torque is up from 135lb ft to a muscular 173lb ft - a healthy advantage over the 320i. Let's see if it's a telling one. ALL THREE CARS PERFORM WITH UPLIFTING vigour. Even though the test Xantia failed to match Citroën's claims - it was nearly a second adrift from rest to 60mph - it feels the most gutsy and eager to please. Torque's the secret - velvet-swathed towque that virtually eliminates NVH disturbance. Who needs balancer shafts? The Citroën's engine may be fairly low-tech - the single-cam eight-valver is a nonentity aesthetically, buried under a porcupine quilt of plumbing and wires - but it works even better in the Xantia than it does in the heavier XM. Only at the extremes of its performance envelope is it less than impressive, but neither sub-1500rpm languor, nor breathlessness above 5500rpm, will trouble the press-on driver. It's second nature to keep the engine spinning beyond 2000rpm where there's instant access to turbo thrust. But for its muscle, you'd be hard-pressed to telll this low-pressure blower was force-fed at all. Belted through the gears to its impressive 135mph max, the Audi - which has the best power-to-weight ratio and the least drag - is the fastest car here, though the margin of its superiority is hardly decisive. Despite breathing so freely through five valves per cylinder - three inlets and two exhausts - it is beaten on torque by the larger-engined Citroën: as the saying goes, there's no substitute for cubic inches. Like the Xantia, the 1.8T is quickly into its stride, untroubled by lag (torque peaks at a lowly 1750rpm) but more top-endy,

'The Citroën's wonderful hydro-pneumatic trickery makes the Audi and BMW seem positively primitive'

Xantia is the only one of the three with a hatchback tail (top left). Just eight valves in its transverse engine (above left) but a turbo makes the difference: it's by far the gutsiest car here. Cabin is the roomiest but the driving position is flawed.