E89 Z4

BMW SHOCKED purists when its third-generation rear-drive roadster – the E89 Z4 – adopted a folding hardtop instead of the more traditional fabric roof option.

This marked a change in BMW’s focus for the Z4, shifting it form being a hardcore Porsche Boxster rival to a cruisier (though still very sporting) Mercedes-Benz SLK competitor.

This move also effectively saw the newcomer replace the E86 Z4 Coupe.

Production source also change, from Spartanburg in the US (home of the X5 and X6 SUVs) to Regensburg in Germany, alongside the 1 Series and 3 Series cars of which the latest Z4 shares it platform with.

Now larger and heavier, the Z4 Roadster brings all-new exterior and interior designs, and introduces BMW’s iDrive cockpit interface system and seven-speed double-clutch transmission (on the twin-turbo flagship) for the first time.

Apart from added security and refinement, the folding metal roof improves visibility via a 52 per cent bigger rear window and a longer side glass area, but adds 30kg to overall weight gains of up to 100kg, thanks to extra equipment and the larger body, which BMW says is also stronger than that of the SLK and Boxster.

The range opens with the entry-level 150kW/250Nm 2.5-litre sDrive23i, the mid-range sDrive30i uses a 190kW/310Nm 3.0-litre petrol six, while the sDrive35i is powered by BMW’s 225kW/400Nm 3.0-litre twin-turbo direct petrol injection inline six.

Safety features include twin front and side/thorax airbags, a pair of fixed rollover hoops, an electronic stability (DSC) and traction (DTC) control system with anti-lock brakes (ABS), cornering brake control (CBC), electronic differential lock, cruise control with brake function, run-flat ‘safety’ tyres with pressure indicator, Servotronic electric power steering, and two three-point seatbelts with pretensioners and force-limiters.

All Z4s included automatic wipers and headlights, front and rear parking sensors, leather seat trim, electromechanical handbrake, dynamic drive control (DDC) variable maps for both engine and steering, bi-Xenon headlights with washers, heated buckets seat, climate-control air-conditioning, 17-inch alloy wheels, power windows/mirrors, a trip computer, and AM/FM/CD audio with USB interface and aux-in slot.

August 2010 saw the arrival of a hot sDrive35is version, producing 25kW more power and 50Nm more torque than the sDrive35i, lifting engine performance to a healthy 250kW at 5900rpm and 450Nm of torque.

An overboost function allowed for an extra 50Nm to be brought on stream for short bursts.

The standard dual-clutch, seven-speed automatic transmission had a launch control function, which helped to explain the super-fast sub five-second 0-100km/h sprint time, meaning the roadster was about as quick as the M3.

In November 2011 the Bavarian brand dropped naturally-aspirated six-cylinder engines from the Z4 in favour of the new turbocharged N20 TwinPower four-cylinder in two states of tune.

Four-pots also got the $3500 option of a new eight-speed automatic transmission with paddle-shift.

In three-litre 30i-replacing 28i guise it produces 180kW, which although 10kW down on its predecessor is compensated by a 40Nm increase in torque to 350Nm, enabling the 0-100km/h sprint to be dispatched in 5.7 seconds – a tenth quicker than before.

Fuel consumption plunged 21 per cent to 6.7 litres per 100km, placing the 28i into the government’s fuel-efficient category under Luxury Car Tax rules, resulting in a hefty price drop.

It was a similar story for the detuned 20i, which replaced the 2.5-litre unit of the outgoing 23i to create a new base model.

Peak power was 15kW down over the old 150kW unit but torque was up 20Nm and fuel consumption equalled that of the 28i.