At the same time as BMW is launching an updated, newly powered Z4 Roadster Series, the Bavarian automaker is also unveiling a BMW M version of this spirited 2-seater: the M Roadster, which takes the Z4’s innate sportiness to an even higher level of thoroughbred performance and driving pleasure.
When the current Z4 Roadster was introduced in the 2003 model year, BMW kept a possible M version under consideration. Then, as now, the Z4 Series consisted of two models powered by regular-production BMW 6-cylinder engines. Now, though, the decision is in: Alongside the now improved regular-production Z4s (themselves powered by BMW’s new magnesium/aluminum Valvetronic 6-cylinder engine), a new M Roadster makes its debut, with production beginning in January ‘06 at BMW’s Spartanburg, South Carolina factory. Base price for the new M Roadster is $51,995 including destination.
With the M Roadster, BMW brings together the Z4’s advanced sports-roadster concept and a version of the BMW M 6-cylinder engine that’s even more powerful than that of the previous M Roadster - plus a wide range of new BMW and BMW M developments in suspension, steering, brakes, stability systems, safety features and, not to be left out, luxury and convenience feaures. In short, the new M Roadster is an artful fusion of ultimate BMW M performance, contemporary technology and abundant luxury.
The BMW M 6-cylinder engine: thoroughbred performance machine
Statistically speaking, the results are dramatic: delivering 330 horsepower at a high-revving 7900 rpm, the internally designated S54 engine propels the 3200-pound Roadster to 60 mph in just 4.9 sec. Maximum speed is electronically limited to 155 mph; speculation about what the top speed might be without the limiter will intrigue enthusiasts, but BMW makes no claim in this regard.
Unlike other 3 Series engines, which employ lighter materials for their block and cylinder head, the S54 combines a cast-iron block with its aluminum head; this was adopted to achieve the engine’s 3.2-liter displacement without lengthening the block.
The block accommodates this engine’s bore and stroke of 87.0 x 91.0 mm, both larger than the dimensions of BMW’s 3-liter engines. However, playing larger roles than increased displacement in the 75-hp increase over the most powerful regular-production 6-cylinder engine is the M3’s induction, combustion and exhaust engineering, together with its execution as a high-rpm engine. The starring role here is played by a cylinder head that could be termed “exotic.”
The S54 engine manifests an important BMW M tradition: an individual throttle for each cylinder. Positioned much nearer to the cylinders than a single throttle can be, these bring atmospheric pressure practically right to the cylinder. The “lag time” inherent in airflow into the cylinders is thus greatly reduced and the engine can react more quickly to throttle movements.
The high-rpm concept
High engine speeds are essential to achieving high power from moderate displacement, but they pose challenges; engineers must ensure that durability standards are met at these levels. The S54 engine’s maximum power occurs just below its 8000-rpm limit at 7900 rpm.
To achieve this revving capability, the engineers applied a number of detail measures. A forged, nitro-carbonized steel crankshaft provides great strength in this critical component. Forged-steel “crack” connecting rods eliminate the need for bolt sleeves and thus reduce reciprocating weight.
Electronics play their role too. The engine’s control module - newly developed for the M Roadster application - calculates and adjusts the ignition and fuel injection at each cylinder individually every 6 degrees of crankshaft rotation, it. Ignition occurs through a very small-diameter “pencil” coil at each cylinder.
Like the M3s, the Roadster comes with a 6-speed manual transmission.
The M Roadster chassis: extensive new engineering by BMW M
New front suspension. While retaining the Z4’s basic concept - strut-type with forged-aluminum lower arms - the M engineers created an essentially new version with:
- A wider front track (by 0.5 in.)
- Newly configured lower arms, still of forged aluminum; more complex shape with open sections for lightness, similar to those of M3s
- New steering knuckles, bolted to the struts (saves weight, sharpens steering response)
Rear suspension. Though modifications to the Z4’s Central Link (multi-link) rear suspension are less extensive than at the front, they are significant. Among others, the following major M elements are shared with M3s:
- Rear subframe - larger and stronger; accommodates differential with M Variable Differential Lock
- Wheel bearings
- Central (longitudinal) Links
- Arrangement of anti-roll bar
BMW M’s most advanced brake system
The M Roadster comes standard with BMW M’s most elaborate brake concept, one that is part of the M3’s Competition Package and is standard on the M5: compound, cross-drilled 4-wheel ventilated discs.
Wheels and tires: ultimate style and grip
Except for wheel design, M Roadster wheel and tire equipment is the same as that of M3s. M Double Spoke wheels, with a very open configuration to help get plenty of cooling air to the brakes, complement the Roadster’s body with a boldly sporty, yet elegant design. Sized 18 x 8.0 front and 18 x 9.0 rear, they are connected to the road by suitably wide, low-profile, high-speed-rated tires sized 225/45ZR-18 front / 255/40ZR-18 rear .
The M Roadster look: subtle and purposeful
At the front, there is a complete new fascia - bumper, spoiler, grille framing - that makes a statement both esthetic and functional. The traditional BMW “kidney” grilles are set deeper into their openings. Their vertical slats are black, harmonizing with the three black-trimmed air-intake openings underneath. To satisfy the engine’s and brakes’ cooling requirements, these are somewhat larger than the new Z4’s single opening. Standard Xenon headlights with auto-leveling include BMW’s popular luminous rings on the inboard lamps, functioning as parking lights but also remaining illuminated when the headlights are on. A high-intensity headlight cleaning system is also standard.
As on Z4s, the hood is aluminum, positively influencing weight distribution and overall vehicle weight; it includes two longitudinal “precision lines” not present on Z4s. At the sides, the 18-in. M Double Spoke wheels and their ultra-low-profile performance tires reflect the Roadster’s performance priorities, while an M logo just behind the characteristic Z4 diagonal slash and its BMW logo-cum-turn indicator confirms the Roadster’s heritage.
In its rear view, the Roadster also has its own bumper ensemble; this includes a diffusor and cutouts for the four chrome exhaust tips. As on ’06 Z4s, the taillights are new, and feature upper sections with three horizontal LED strips; these sections serve the second stage of illumination provided by BMW’s Adaptive Brake Lights under hard braking. The M logo appears again here, on the left side of the trunklid.
Softtop and interior: M also means luxury
The M Roadster embodies the best of Z4 luxury and then some.
Standard, for example, is the fully automatic softtop, which comes in a choice of three colors and includes an interior lining for enhanced weather protection. The rear window is glass, and includes heating. Like the Z4, the M Roadster has a variable storage compartment for the softtop, which allows greater trunk space when the top is up; however, compared to the Z4 Roadster, the M’s trunk has about 3/4 of a cubic foot less volume because its battery and the M Mobility System are carried within the trunk space.
Doorsill trims display the M logo (with its three colors) in a large, handsome format. Once inside the M cockpit, the driver and passenger enjoy a uniquely sporty, high-quality atmosphere blending BMW M’s style of abundant luxury with typical BMW functional design. Premium Nappa leather M sport seats (choice of manual or power) include embossed M logos on the head restraints. Leather also appears on the door panels, console armpad, kneepads, handbrake grip and shift knob. Trim materials are special: The largest areas (across the dash, center console) are in a sporty-technical Aluminum Hexagon surface, while pearl-gloss galvanic trim appears on the climate controls, interior door handles and pulls, and the “tubes” into which the main instruments are recessed. Automatic climate control is standard in the M, and its rotary knobs also include the new rubber touch surfaces that enhance their tactile feel.
An extensive complement of safety engineering and features
Every current BMW incorporates from-the-wheels-up engineering and technology for active safety - the kind that helps drivers avoid accidents - and passive safety - features that help protect the occupants should an accident happen. The BMW M Roadster’s handling and braking capabilities, described earlier, are the active side; occupant-protection features include the following and more:
- Dual front-impact Smart Airbags
- Automatic safety-belt tensioners and force limiters
- Seat-occupation detection on passenger’s seat
- LATCH attachment of child-restraint safety seat to passenger’s seat
- Side-impact airbags
- Rollover Protection
- Battery Safety Terminal
- Intelligent Safety & Information System for deployment of safety devices and systems