The first prototypes of BMW's all-new E90 3-series, which is due to be launched at the 2005 Frankfurt Show, are now venturing out of the proving ground for extended testing. And although the cars are heavily disguised, it appears the E90 may be the least adventurous of Chris Bangle's recent designs.

That makes sense, as the 3-series is BMW's cash-cow, accounting for about half the company's total sales worldwide: BMW simply can't afford for the E90 to polarise consumers as violently as the new 7-series and 5-series models have.

The E90 will therefore follow a tried and true formula. Munich sources hint the car may even be positioned as a 'back to basics' BMW, with an emphasis on reduced weight and crisper chassis dynamics. The E90, which will be built in an all-new plant near Leipzig, will be about the same size as the current E46 3-series, although the wheelbase may be stretched by an inch to improve legroom for rear seat passengers.

Volume selling models will be the saloon and estate versions, although with the launch of the X3 urban off-roader, debate rages in Munich over whether the estate should have a higher roofline to position it as a pseudo-MPV. The other big change is that the coupe and convertible versions may be badged 4-series in line with BMW's strategy of separating its mainstream cars from the overtly sporting models.

Drivetrain configurations will follow familiar BMW practice, with entry level models getting four- cylinder petrol and diesel engines, and upscale variants inline six-cylinder petrol and diesel engines. BMW sources hint the range-topping M3 saloon and M4 coupe may be powered by a 4.5-litre direct injection V8 with 4000bhp.