Caterham Superlight R400

Irregular? The firm's new R400 is in no way conventional transport - not all cars can cover the 0-60mph sprint in 3.9 seconds. Pastime? Well, given the R400's motorsport potential and the amount of non-essential driving any buyer will do, is there any other way to describe the ownership experience?

Caterham launched its XPower Superlight range a year ago in a tie-up with MG Rover. First came the no-compromise 230bhp R500, and then the slightly saner, cheaper 160bhp R300. Now, with the arrival of the 200bhp R400, enthusiasts can choose from a triumvirate of mad roadsters.

But at ΂£29,950 the middle 'R' isn't exactly cheap. The ΂£6,000 price premium over the R300 does buy a race car-style dry-sump oil system, carbon fibre nose, wings and protectors, a limited-slip differential and a new digital dashboard layout. And, of course, an extra 40bhp in a model that weighs 10kg less. But out on the open road, is it really worth paying the extra?

As you'd expect of such a raw car, the throttle is very sensitive - overly so for everyday use. But with a clear road - or track - in front, the R400 is truly in its element. Hit the throttle and the extra horsepower catapults the Caterham forward, exhaust screaming. Take it up to 10,000rpm and an LED shift indicator behind the wheel tells you when to change gears.

Chassis, steering and suspension are identical throughout the Superlight range, so you're treated to the same direct feel and cornering agility already witnessed on the other two cars. Few machines this side of a race circuit offer more thrills or driver feedback.

However, the carbon fibre trim won't be to all tastes. And although owners are prepared to put up with the looks and extra cost of the new digital dash simply to shave a few grammes off the weight, we'd prefer the analogue dials used on previous Sevens. We love the dry sump and limited-slip differential, though, as these mark out the R400 as a cut above the R300. The sump helps the engine's performance and lowers the centre of gravity to improve handling, while the diff makes it easier to get the power down out of corners. Both are especially important if buyers are considering track-day use.

Yet despite all this, we can't help thinking the marginally slower R300 is the more financially sensible option, as it is no less enjoyable on the road. Adding dry-sump lubrication and a limited-slip diff would boost the cost of that car to only ΂£25,625 - still more than ΂£4,000 short of a base R400. To save a little more, you could build it yourself from a kit - just like a jigsaw.