Spy shots circulating over the past few months suggested that BMW's new Z4 roadster would utilise a folding hardtop, so it was no surprise to receive the first official information from BMW this week on its two-seater, though there is even more of interest hidden under the attractive new skin.

First up is the optional fitment of Adaptive M Suspension (AMS), which features electronically controlled dampers with three settings, accessed via a switch on the centre console similar to that employed on the new BMW 7 Series. Curiously, BMW reckons that the firmest setting, where the ride height is also dropped 10mm, is comparable in comfort to the standard suspension of the original Z4, suggesting that the new car will be more comfortable in general.

However, it's thought that the new Z4 will appeal to a wide cross-section of buyers thanks to the new Drive Dynamic Control function that allows the driver to alter steering and throttle calibrations, the AMS, level of traction control and gearchange strategy (on the automatic models) by the touch of a button.

At launch, three six-cylinder engines will be offered, and the Z4 will use a new naming strategy. Entry-level models are designated sDrive23i - though in fact the powerplant is 2.5-litres in capacity. The benchmark 0-62mph sprint is covered in a respectable 6.6 seconds, while top speed is 151mph. BMW also claims 33.2mpg on the combined cycle and 199g/km of CO.

The sDrive30i is powered by a 3.0-litre version of the same engine and puts out a useful 254bhp and 229lb.ft of torque to the rear wheels. The 0-62mph time is slashed to 5.8 seconds, while top speed is electronically limited to 155mph. Despite the boost in performance, the sDrive30i returns identical economy and emissions figures to the sDrive23i model.

We can forgive the top-of-the range sDrive35i's 219g/km and 30.1mpg though, as it's powered by BMW's formidable twin-turbo, direct injection straight-six. Power peaks at 302bhp and up to 295lb.ft of torque is on tap. Only 5.2 seconds after a standing start, the sDrive35i can theoretically hit 62mph. That time can be reduced by a further 0.1 seconds if the Double Clutch Transmission (DCT) is fitted. The DCT also has the effect of lowering fuel consumption and emissions.

Unfortunately, the sDrive35i model is the only Z4 to come with the option of the sporty new seven-speed, dual-clutch transmission, with a conventional six-speed automatic optional on the other models - a six-speed manual is standard across the range.

Although the new BMW Z4 borrows its proportions from the outgoing car, there have been modest increases in length and width and the new roof also liberates extra headroom (yes, even when it's up). The compact, two-piece hard top takes only 20 seconds to operate, though sadly reduces boot space from a maximum of 310-litres to 180-litres. There is some additional oddment space behind the seats and BMW will offer buyers the option of a through-loading system to enhance practicality.

But who buys a two-seat sportscar for its practicality? First impressions of the new shape are favourable and that's probably the most important aspect of this car. However, buyers will have to wait until May 2009 to get their hands on the new Z4. We should have further specification and pricing information ahead of that.

Shane O' Donoghue - 13 Dec 2008