Traditional practice dictates that the German-based automaker introduce new or significantly upgraded powertrains in its sedan lineup before installing them in its "Z" sports car. The same holds true again this year, but the Z4, which arrives in May, has also been fitted with revised sheetmetal plus a consolidation of separate coupe and convertible body styles into a single (and convenient) have-it-your-way configuration.
Hardtop-convertibles aren't the latest Big Thing in vehicle design. Among the current crop are the Chrysler Sebring, Volkswagen Eos, Mazda MX-5 and Volvo C70. As well, BMW recently installed its first-ever folding roof when it upgraded the 3-series convertible.
The advantages of a retractable hardtop, such as improved weather/security protection, a quieter cabin and added structural integrity, are important assets when applied to a sports-car platform. The Z4's two-piece aluminum unit can be automatically raised in just 20 seconds by activating a console-mounted switch or an optional remote control button on the key.
To provide sufficient storage for the new cover, more than 12 centimetres of length has been spliced into the back of the car. That also means more room behind the seats where you'll find a removable partition separating the trunk and top stowage zones. Buyers can also select an optional pass-through into the cabin so that skis and other longer items can be brought along for the ride.
Other key dimensions remain fairly steady, although BMW has managed to dial a bit more shoulder and elbow room into the revised cockpit.
Despite the added length, the Z4, which now weighs about 100 kilograms more than a 2008 Z4 ragtop, appears generally similar to its predecessor. Subtle sheetmetal changes include a restyled front and rear end, added character lines in the hood and more streamlined door and fender panels that replace the previous model's somewhat jarring creases. These modest adjustments give the Z4 a thinner and more athletic stance.
The base sDrive30i is equipped with a 255-horsepower 3.0-litre inline six-cylinder engine, while the sDrive35i runs with a twin-turbocharged version of the 3.0 that puts down 300 horses. That's a significant jump from last year's 215- and 255-horse base and optional engines.
A six-speed manual transmission is standard. A six-speed automatic is available on the sDrive30i, while a seven-speed "double-clutch sport automatic" (essentially an automated manual that lacks a clutch pedal) gearbox is optional on the sDrive35i. Both automatics come with steering-wheel-mounted paddle shifters. BMW claims the twin-turbo Z4 will accelerate to 60 mph (96 km-h) in 5.0 seconds (0.6 seconds quicker than the base car). That compares with the previous Z4 M and its 330-horsepower 3.2-litre non-turbocharged six-cylinder engine.
Along with a wealth of standard equipment, BMW's brand of traction and stability and control is built into the Z4. The latter helps keep the car headed on the intended path when encountering slippery conditions. The system, which keeps the brake linings dry for more consistent performance, will also pre-load the brakes when it senses an impending panic stop.
There are also three driver-selectable settings (Normal, Sport and Sport+) for ride height, suspension firmness, power-steering response and throttle sensitivity. The highest mode, Sport+, limits the Z4's stability- and traction-control interference. It's still there, but it allows slight wheelspin.
In addition, the standard leather seats have been treated with a special material designed to stay cool by reflecting, instead of absorbing, the sun's rays.
On the option sheet is a centre-console controller, called iDrive, that operates the navigation and communication systems.
The newly dressed and enlivened Z4 is suddenly a more practical and responsive roadster that should suit drivers desiring more fun in the sun, or whatever the weather deities throw at them.
WHAT YOU SHOULD KNOW 2010 BMW Z4
Two-door, rear-wheel-drive hardtop convertible roadster.
3.0-litre DOHC I6 (255 hp); 3.0-litre DOHC twin-turbocharged I6 (300 hp)
Six-speed manual; six-speed automatic; seven-speed automated manual (turbo).
With increased size and heft, the Z4 heads up market as more of a touring machine than a sporty runabout.
* Evolutionary design stays true to original Z4, but with added stowage space.
* New engine lineup a step forward in performance * No plans to introduce V8-powered M roadster (yet) * Too bad BMW's AWD system isn't on the menu.
* At 1,150 kilograms, Z4 out-hefts competitors by 80-220 kilograms.
* Who is ever going to remember/use unnecessarily awkward Z4 model names?
Front airbags; side-impact airbags; anti-lock brakes; traction control; stability control.
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