As auto enthusiasts know, the “M” in BMW’s automobile nomenclature means “fast.” The Z4 M Roadster hikes the bar on a sports car that is considered a class leader.
BMW engineers have transplanted the running gear and powertrain of the very competent M3 sedan to the Z4 sports car. Here’s how it works. The M3’s suspension components are tuned to the Z4 Coupe and Roadster. For example, the spring rates for the Coupe are higher and the damping more aggressive when compared to the Roadster’s settings. Both Z4 Ms use the M3’s front struts and rear multilink suspension, rear subframe, limited-slip differential (M Variable Differential Lock), rear anti-roll bar mounting points, wheel bearings, and front control arms, while the vented, cross-drilled rotors and single-piston calipers were brought over from the M3 Competition package.
Further, the short-throw, well-spaced six-speed manual gearbox also comes over from the M3. Hydraulically assisted rack-and-pinion steering replaces the normal electric power unit of the Z4s, which has led to some critical reviews regarding the Z4’s lack of subtle steering feedback. Add it all up, and the sum is greater than the parts, as the lighter Z4 M is a more willing and superior performer on the track.
BMW also did a heart transplant on the Z4 by again referring to their M3 donor for its jewel of a motor. The award-winning S54 inline six uses a cast iron block so that its 100-plus hp per naturally aspirated liter can be safely contained within its 3.2 liters. The engine is crammed with BMW technology: six individual throttle bodies, DOHC, 24 valves actuated by the Double VANOS variable valve timing system, and an 11.5:1 compression ratio. All this produces 330 hp at 7,900 rpm – just 100 rpm short of the engine's 8,000-rpm redline and 3 hp less than in the M3 due to exhaust system constraints – with 262 lb-ft of torque at 4,900 rpm and 80% of that maximum torque available from 2,000 rpm. The EPA estimates 16/24 mpg, and Road and Track observed 19.9 mpg in its comparison test of an M Coupe against a Porsche Cayman S.
Cram all that power in a two-seater that’s 117 pounds lighter than the donor M3, and Car and Driver was able to rip a 4.6-second 0-60 blast in an M Roadster. However, running through the twisties, specifically those on the Nordschleife (the Northern Circuit of Germany’s Nurburgring), the M Coupe outran the M Roadster and the M3. Reviewers raved over the M’s handling. They found that the Z4 M has a hard edge to it. A Road and Track editor commented that it felt like “a German Viper” - more refined, “but still with that aggressive, powerful nature.” Reviewers seemed addicted to ripping off 8,000-rpm shifts and powering out of perfectly carved corners. Car and Driver recorded 0.90 g on their skidpad and compared the car to a cheetah. Continuing the characterization, they found that a car capable of “feline responses” is one that offers only a “modicum of compliance” in the daily drive – while not “a go-kart,” you will know “every expansion joint and concrete patch the tires encounter.” The Z4 M exhibits minimal understeer that can be easily corrected with the throttle.
The interior is elegant and business-like - that business being the road. The well-bolstered seats are M sport buckets - they hold you in place and place you within perfect reach of everything necessary to work the car’s driving potential. The steering wheel telescopes and tilts to aid in achieving your perfect fit. Yet the combination of wood, leather, and brushed aluminum trim bits let you know it’s a BMW cockpit. The standard automatic convertible top takes 7 seconds to drop and is equipped with a heated rear glass window. The convertible top retains a usable 8.5-cubic-foot trunk, as it becomes its own tonneau cover when folded.