DETROIT – In a world premiere that briefly tries to shift the focus from the gloomy weather and even darker automotive outlook, BMW AG unveils the latest generation of its sexy Z4 roadster at the North American International Auto Show here.

The convertible features a highly sculpted exterior design and retractable hardtop, in place of the previous-generation’s fabric top.

The new roof is comprised of two aluminum shells that fold into the trunk in 20 seconds, while allowing enough room for a medium-size suitcase or one golf bag. With the roof up, the car can accommodate two golf bags, BMW says.

The Z4’s exterior design features short overhangs, a long hood and a seating position close to the rear axle. This architecture, plus rear-wheel drive and near-perfect weight distribution separates the new roadster from two dozen other convertible competitors, BMW says.

The new-generation Z4 is 5.8 ins. (15 cm) longer, 0.4 ins. (1 cm) wider and 0.3 ins. (0.8 cm) lower than the previous iteration. Wheelbase also has grown .01 in. (0.3 cm) to 98.3 ins. (250 cm).

In the U.S., the car will be available with two 3.0L inline 6-cyl. engines.

The more powerful mill is BMW’s 300-hp twin-turbo I-6, which enables the roadster to accelerate to 60 mph (97 km/h) in as little as 5.0 seconds. The less-expensive engine is the naturally aspirated 3.0 I-6 that produces 255 hp and hits 60 mph from a standstill in 5.6 seconds.

A 6-speed manual is standard on both. A dual-clutch 7-speed sport automatic and a 6-speed sport automatic with paddle shifters also are available.

dwinter@wardsauto.com