Finally, the camshafts and inlet and exhaust manifolds have been constructed using hydroforming - the high-pressure water shaping of metal. The result? Thinner, lighter yet stronger components.


Sport automatic gearbox

The concept of a sporting automatic gearbox was, until recently, something of an oxymoron. BMW's Steptronic gearbox was introduced as an option in the BMW 750i/iL in September 1995 and offered greater driver interaction than the previous automatic gearbox. Sports-minded owners had the option of letting the gearbox self-select around town, but manually select the gear when driving more spiritedly. 

BMW's new Sport automatic gearbox in the Z4 3.0si Coupe takes BMW automatic gearboxes to a new level and offers drivers the choice of three selection modes; automatic, manual selection using the gear lever (Steptronic) and now, manual selection using steering wheel-mounted paddles. A Sport automatic-equipped car also changes gear in half the time of a conventional auto gearbox, delivers a 40 per cent improvement in the gearbox response time and even blips the throttle on down-changes for a sporting sound track and smoother transition between gears. 

To change the selection mode, the driver simply changes the position of the gear lever or pulls one of the paddles. The normal automatic mode is re-activated if the driver doesn't touch the paddles or the selector lever for over 12 seconds.

This paddle-shift system is completely different to the well-known BMW SMG systems, which are based on a manual gearbox.



Chassis and suspension

By the time BMW engineers got the green light for the Z4 Coupe, the Roadster was already 'signed, sealed and delivered'. Taking the Roadster as a basis, the Coupe began life with one of the stiffest body structures ever developed for a convertible. Body flex or scuttle shake had virtually been eliminated. With the addition of a roof structure to add further rigidity, a suspension set-up tuned on the punishing Nürburgring and a braking system borrowed from the legendary M3 CSL, the new Z4 Coupe comes as close to BMW's aspiration of 'the Ultimate Driving Machine' as any current, or previous, car in the range.



Body and chassis - building on a strong foundation

From the outset, designers and engineers focussed on a number of key chassis attributes with the aim of making the new BMW Z4 Coupe the best driving car in its class. The result is an agile and dynamic Pocket GT that, in testing, has competed with the best two-seater sports cars in its segment.

Of prime importance is a rigid body structure. Building on the exceptional torsional strength of the Roadster (14,500Nm/degree), the addition of a fixed roof took the Coupe to another level. At 32,000Nm/degree, the new Z4 Coupe has the stiffest body structure in its segment. Under floor Y-arms connect the bulkhead, doorsills and transmission tunnel. These combine with reinforcement bars and panels under the floor, on the spring-strut turrets and around the windscreen frame to provide further body stability. The Z4 Coupe requires no further weight-increasing vibration damping. 

A low vehicle weight and low centre of gravity are also of paramount importance. The programme of weight saving in the drivetrain has already been outlined, but the Z4 Coupe also features lightweight technology such as an aluminium bonnet and suspension components. As a consequence, the new Z4 3.0si Coupe weighs in at 1,395kgs and 1,495kgs for the high-performance 3.2-litre M Coupe - only 10 kilogrammes more than the Z4 M Roadster. 



Suspension and brakes - derived from BMW M3 CSL

The Z4 Coupe's front suspension consists of a spring strut structure front axle with forged aluminium track control arms, twin-sleeve gas-pressure shock absorbers, rack and pinion steering and an anti-roll bar.

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