BMW has made a hard choice with its Z4 sportscar next year, after revealing it will come with a two-piece, electro-hydraulically operated Retractable Hard-Top roof that can be raised or lowered in 20 seconds.

The new roadster is also the first vehicle to be offered with Adaptive M Suspension. Electronically controlled dampers offer three different configurations and lower the ride height by up to 10mm for a more dynamic drive. By way of comparison, the Sport+ setting of the new car is comparable to the outgoing Z4’s standard ride comfort level.

Drive Dynamic Control function is another first and allows the driver to alter, depending on model specification, the throttle and steering response, level of ride comfort, Dynamic Stability Control response and, on automatic or Double Clutch Transmission cars, gear change times.

Powering the new BMW Z4 is a choice of three six-cylinder powerplants. The range flagship is the current International Engine of the Year-winning 3.0-litre twin-turbocharged engine. Producing 306bhp the BMW Z4 sDrive35i powers its way from zero to 62mph in 5.2 seconds (5.1 seconds for a Double Clutch Transmission-equipped car) and on to an electronically-limited top speed of 155mph. It also records a combined fuel consumption figure of 30.1mpg (31.4mpg) and CO2 emissions of 219g/km (210g/km).

Joining this model in the launch line-up will be the Z4 sDrive23i and the Z4 sDrive30i. Both use the same magnesium aluminium alloy engine with Double VANOS and VALVETRONIC technology, but with varying capacities.

The 2,497cc entry-level Z4 sDrive23i produces 204bhp which equates to a zero to 62mph time of 6.6 seconds (7.3 seconds for the Sport Automatic) and a top speed of 151mph (149mph). In contrast the Z4 sDrive23i is capable of 33.2mpg (34.4mpg) on the combined cycle and CO2 emissions of 199g/km (192g/km) respectively.

The BMW Z4 sDrive30i comes with a 2,996cc powerplant offering 258bhp and records a zero to 62mph time of 5.8 seconds (6.1 seconds for the Sports Automatic) and an electronically-limited top speed of 155mph. It posts 33.2mpg (34.0mpg) and 199g/km (195g/km).

Transmitting the power to the road in all three versions of the BMW Z4s is a six-speed manual gearbox as standard.

Customers of the Z4 sDrive23i and the Z4 sDrive30i can specify a six-speed Sport Automatic transmission featuring gear change paddles on the steering wheel.

Buyers of the Z4 sDrive35i can choose the more advanced seven-speed Double Clutch Transmission, again with gear shift paddles located on the steering wheel.

All of the BMW Z4s come as standard with facets of BMW’s award-winning EfficientDynamics programme such as Brake Energy Regeneration, Electric Power Steering with Servotronic and Reduced Rolling Resistance Tyres.

The new BMW Z4 is larger than its predecessor measuring 148mm longer at 4,239mm and 9mm wider at 1,790mm, and this results in greater interior space and luggage capacity.

With the roof up, headroom has been increased by 44mm while the greater car width and design enhancements have led to 20mm more shoulder room and 43mm more elbow room.

For the first time on a BMW Z4 there is a bespoke storage facility located behind the driver and passenger seats.

This approximate 15.5-litre single compartment stretches the width of the car’s interior and features netting to hold the contents in place. It can be complemented by an optional Storage Package that adds further stowage capacity.

BMW’s latest generation of iDrive makes its first appearance on a Z4.

The BMW Professional Multimedia Navigation system features a hard disc drive capable of 12Gb of audio file storage and BMW ConnectedDrive functionality.

The system also comes with eight programmable Favourite buttons as system shortcuts.

The folding roof construction of the BMW Z4 creates a boot that varies in capacity from 180 to 310 litres.

For the first time on a BMW Z4 customers can specify a through-loading system for additional storage capability.

A hatch between the two seats permits a second full set of golf clubs to be carried.

Driver visibility in the BMW Z4 has also been improved.

The all-new BMW Z4 will go on sale in May 2009 with prices to be announced.