During the reign of BMW's Z3 roadster (and later Z3 coupe), availability of a performance-packed M-editon became a major element of the sports car's allure. Yet, when BMW launched the Z4 - successor to the Z3 - an M-edition was absent.
That lack has been remedied with the Z4 M-Roadster, launched during the 2006 model year: specifically, last spring. In addition to a bigger and stronger engine, with a long list of performance-oriented internal components, the M-Roadster gets a modified suspension with lower ride height and slightly wider front track.
A new front fascia has been developed for the M-Roadster. Traditional twin "kidney" grilles sit deeper than on the regular Z4, with vertical black slats. The aluminum hood features additional contour lines. Weight distribution is a virtually even 50.7/49.3 percent (front/rear).
Four chrome exhaust tips release gases from the 3.2-liter inline six-cylinder engine, which generates 330 horsepower at a rapid-revving 7900 rpm. That's 75 more horses than a regular Z4's engine delivers. Among other revisions, there's an individual throttle for each cylinder in the M-Roadster. Also, in this age of all-aluminum powerplants, the engine uses a cast iron block with an aluminum cylinder head.
A ZF six-speed manual gearbox sends all those horses to the road. M Dynamic Driving Control provides Normal and Sport modes that affect throttle response. When Sport mode is selected using the console switch, the ratio of the throttle opening to pedal movement increases, yielding what BMW calls "apparent" quicker engine response. No extra burst of engine power occurs, but the system is designed to make it feel as if that's the case. Dynamic Stabiltiy Control optimizes traction in this rear-drive roadster.
Special features include a Start-Off Assistant, which keeps the M-Roadster motionless on an uphill incline, while waiting for the next takeoff. Hydraulic power steering is used, rather than the Z4's electric setup. Compound, cross-drilled ventilated brake discs are made with two-piece rotors, and M Double Spoke wheels hold 18-inch tires.
Side-impact airbags are installed, and the battery sits in the trunk. A heated glass rear window is mounted in the automatic-opening fabric top.
BMW claims that the M-Roadster will accelerate to 60 mph in 4.9 seconds, and that figure sounds about right after trying a few energetic takeoffs. This is one serious sport machine, though, which means it's not the easiest car to drive. Manipulating the six-speed's gearshift and turning the wheel demand a certain amount of effort, which can become tedious on a longer drive. Overall, the M-Roadster has a heavy feel, from its ride to its clutch operation.
Enthusiasts are sure to consider the result to be well worth any increased exertion, but casual drivers might be less enthralled. Of course, they're not the marketing targets for BMWs of this caliber. This is one utterly serious sports car. That means getting inside, too, can be a battle that demands some significant head-ducking with the top up, as in the regular Z4. Once there, however, space is isn't bad for two passengers.
Gauges are deep-set and not always easy to read, and controls are somewhat oddly laid-out. Exhaust noise and vibration can be troublesome to sensitive ears. All told, the M-Roadster is one great sports car on a track or through winding mountain roads, but not so enticing for everyday commutes.
How much will all this extra performance set you back? The M-Roadster stickers for $52,995 (including destination charge), versus $37,095 for the current regular Z4 convertible.