Motoring: Why the latest Big Idea is not so big

PLATFORMS WERE funny shoes worn in the Seventies and are the things you stand on while you wait for your train to be delayed. Now they're all the rage in the car industry.

"Platform strategies" mean more choice for the customer and cheaper cars for the manufacturer. On the face of it, they are thoroughly good things. But there is also an insidious side to this latest Big Idea from the car industry, especially if you're in the market for a "prestige" car.

A platform strategy enables a mass car maker to offer many different models using very few different sets of mechanical components. A single platform - suspension, engines, gearboxes and many other auxiliary bits - can sire such disparate vehicles as the Ford Ka, Ford Fiesta and Ford Puma.

Same car, different clothes, different character, different market segment. Ford wins and, because we punters get more choice, we win too. In the case of Ford, all three cars are roughly the same size and the same price, so there is minimal compromise in sharing parts.

Where the platform strategy can potentially go wrong is when cars designed for one purpose - a family hatchback, for instance - try to get ideas beyond their station in life. The new Audi TT sports car, one of the most drop-dead gorgeous cars of 1998 and the subject of huge waiting lists in most countries, is - underneath that voluptuous skin - a Volkswagen Golf. Of course this makes it cheaper for Audi to make. Yet others may argue that a premium-brand sports car should not be riding around on the mechanicals of a humble hatchback, never mind that there is a turbocharger installed to add a touch of spice.

There are myriad other examples. The Saab 9-3, which has one of the car world's most desirable badges on its nose and rump, shares the platform of the Vauxhall Vectra, one of Europe's most ordinary cars. It is the 9-3's major weakness. Saab, in the days before General Motors bought it, used to have bespoke mechanicals and were all the better for it. Most Saab owners, of course, have no idea about their cars' humble mechanical ancestry. But, for me, it's a bit like buying a valuable watch only to find that it shares its movement with a pounds 10 Casio. What's unseen is often as important as what's more obvious.

There are very few premium-brand cars that have the hearts of a thoroughbred, contrary to what their manufacturers like to pretend. The Audi A4 is a Volkswagen Passat in drag. It is a fine car, because the Volkswagen group is expert at borrowing and tuning mechanicals. But the Passat, which is cheaper, is also better. Ultimately the A4 is a pointless vehicle, a pretty marketing gimmick aimed at those keen on some badge one-upmanship. Current Rovers are Hondas with chrome grilles and lots of walnut inside. These superficialities cannot compensate for the lack of true mechanical class, no matter how much Rover might pretend otherwise.

One of the keys to BMW's success is that it remains a thoroughbred manufacturer. Its 3-series is not a jumped-up family hatchback, cleverly disguised as a sports saloon. It was designed, from the outset, to be the best possible car of its type. As such, it has rear-wheel drive, because that offers more feedback for the driver, and it offers a straight-six cylinder engine, because that is the optimal configuration for such a car.

Those who use front-wheel drive and four-cylinder motors (virtually all of BMW's rivals in the sports saloon sector) do so because they are following platform strategies. In other words, they are saving money by pooling parts.

This can, of course, also save you - the punter - money. And it's the reason why "prestige" Audis, Saabs, Alfas, Rovers and some Volvos are cheaper. But it's also the main reason why, generally, they are not as good.