Usually a replacement for one of the younger members of the cast, the new actor is generally better looking and more capable than the unlucky person who has been shown the stage door.

A similar thing happened to BMW's Z-car this summer. The Z3 – a two-seater roadster – was the company's first car to be built at its plant in Spartanburg, South Carolina, and while the six-cylinder models held more appeal than the four-cylinder cars, they were rather lightweight in terms of ability.

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Step forward the Z4 - a more purposeful and aggressive looking car, far more handsome than the Z3 it replaces and engineered to entertain in a way the Z3 never was.

The first Z4s were fitted with 2.5 and 3.0-litre engines, but now BMW is introducing an entry-level version with its smallest six-cylinder engine, the 168bhp 2.2i.

What BMW wants to avoid doing is go so small with the Z4 engines that the car is seen as a pricey alternative to the Mazda MX-5 and MG TF, so this six-cylinder model can be viewed as an early attack on the new Mercedes-Benz SLK due to appear in 2004.

The 2.2-litre straight six has been used in the 3-series and 5-series for a few years and also appeared in the Z4's predecessor. Factor in that the Z4 is 30kg lighter than the Z3 and performance should still be brisk.

Body stiffness rivals that of many saloon cars, suggesting that the dreaded 'scuttle shake' found in some convertibles should not be a problem afflicting Z4 drivers.

Standard features include electric windows, trip computer, air conditioning, a CD player, sports seats and run-flat tyres.

The run-flats can be driven for up to 90 miles at speeds of up to 50mph, doing away with the need for a spare wheel and maximising luggage capacity.

Five different alloy wheel options are available, ranging from 16-inches to 18-inches, as well as a choice of satellite navigation systems, Bluetooth preparation and voice activation for telephone and navigation functions.

All Z4s come with an electric folding roof, which takes 10 seconds from roof up to disappearing from view.

For the user-chooser looking for a racy roadster with a premium badge on which to fritter away their monthly cash allowance, the Z4 2.2i with a manual gearbox has carbon dioxide emissions of 214g/km, putting it in the 26% benefit-in-kind tax bracket for the remainder of this financial year, while the five-speed automatic is slightly higher at 226g/km or 29%.

These are slight improve-ments over the more powerful 2.5i, while the good news for fleet managers and leasing companies is that CAP Monitor suggests a residual value of 48% after three years/60,000 miles for the manual and 47% for the auto.

The Z4 only went on sale in the UK in July but BMW has already sold 3,800 Z4s and there are waiting lists for the 2.5i and 3.0i stretching into June 2004. The 2.2i is expected to follow suit with similarly strong demand.

Behind the wheel

SOME new BMWs have polarised opinion with their dramatic styling, and the Z4, along with the 7-series, 5-series 6-series and X3, has come in for some heated debate.

While you can never please all of the people all of the time, I am a fan of the Z4's looks and some of the little design features show that BMW is almost untouchable when it comes to attention to detail. The indicator side repeaters light up orange around a BMW badge in the front wings, a Z shape can be seen in the bodywork, thin front indicators that separate the headlamp from the front bumper, and the integrated rear spoiler in the boot are just a few of the visual delights that await the driver.

The car's interior is plain, simple and uncluttered and there is a wide range of adjustment for the seats and steering wheel to ensure the optimum driving position.

BMW claims the manual Z4 2.2i will sprint from 0-62mph in less than eight seconds and despite having less power and torque than it's siblings, this variant never feels slow. Maximum torque comes in at just 3,500rpm which makes the most of the 155lb-ft available, and at full tilt it is still possible to get a squeal from the rear tyres when changing from second to third.

With the exception of the last few outward miles on our short roof-down route from the BMW Performance Centre at Spartanburg, the Z4 2.2i was driven on urban roads linking small towns. A few level crossings tested the firm but forgiving ride, while the last part of the outward section allowed us to exploit a few of the finer points of the car's handling.

Weighing a little more than 1,300kg, the Z4 2.2i always feels nimble, while the steering has been tuned for feel and feedback. Following challenging bends in the road is a matter of flicking the wrist, while the tyres and 16-inch wheels offer plenty of grip.

Driving verdict

IT might not have the punch of its more powerful siblings, but the Z4 2.2i has their stunning looks. For user- choosers looking for a low tax premium roadster it makes sound sense.

Model: BMW Z4 2.2i
Engine (cc): 2,171
Power (bhp/rpm): 168/6,100
Torque (lb-ft/rpm): 155/3,500
Max speed (mph): 140 (137)
0-62mph (sec): 7.7 (8.3)
Fuel consumption (mpg): 32.1 (30.4)
CO2 emissions (g/km): 214 (226)
Fuel tank capacity (l/gal): 55/12.1
Transmission: 5-sp man/5-sp auto
Service intervals: Variable
On sale: Now
Price (OTR): £24,255
Figures in brackets for auto models