BMW Z4 roadster - Engines, drive & performance

The BMW Z4 may have been developed alongside the Toyota Supra but there are enough differences between the two for each to have its own personality. Among shared components are the BMW-designed engine and automatic gearbox from German company ZF.

The chassis design is common to the two but not shared with any other Toyota or BMW car. To save weight without reducing strength, aluminium is used extensively in the suspension system, and overall weight distribution is 50/50 – a figure that BMW enthusiasts will find familiar and reassuring, as it should provide excellent balance in corners.

The top M40i model gets adaptive dampers as standard and there's an electronic differential designed to boost agility when powering out of tight turns. It ought to be a nimble car – its wheelbase (the distance between front and rear axles) is 5mm shorter than the Porsche Boxster, and some 25mm shorter than the previous BMW Z4. Today's Z4 has a lower centre of gravity than the previous generation too, thanks largely to a traditional canvas roof in place of a heavy folding metal hard-top.

The Z4 is still a heavy car despite the fabric roof. It tips the scales at 1,535kg, making it a considerable 150kg heavier than the Porsche 718 Boxster S, even when the latter has a PDK dual-clutch automatic gearbox fitted. The difference in weight is even more extreme against the Alpine A110, which only weighs 1,080kg. Unsurprisingly, this has quite a bearing on how the BMW feels from behind the wheel.

There'll be few complaints about the BMW's sharp responses – the grippy tyres cut into corners with enthusiasm, and the steering is precise. There's barely any body lean to discourage you from carrying speed through corners, either.

What's lacking, however – and a rare oversight from BMW – is feel and feedback through the steering wheel. Perhaps because there's so much mass changing direction beneath you, the BMW Z4 M40i doesn't feel as delicate as its lighter rivals, and that leaves you feeling a little uninvolved in the driving process.

This feeling is confirmed by the lighter sDrive20i. With a smaller four-cylinder, 2.0-litre engine under its bonnet, the Roadster feels more agile and engaging from behind the wheel, with sweeter steering. It might not accelerate as quickly as the M40i, but in every setting except for the drag strip, it's a more enjoyable car more of the time, and is our pick of the Z4 range.

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BMW Z4 petrol engines

The BMW Z4 M40i has something of an old-fashioned muscle-car feel to it, and a big part of that comes down to its 3.0-litre, twin-turbocharged six-cylinder petrol engine. It's the same engine you'll find under the bonnet of the BMW 2 Series M240i Coupe, and proves more than powerful enough for use in a true sports car. With 335bhp, it'll take the Z4 from 0-62mph in just 4.5 seconds – around the same time, coincidentally, as the Porsche 718 Boxster S takes.

Some will prefer the BMW's raucous six-cylinder soundtrack, too, but a lot of enthusiastic drivers will mourn the fact that BMW doesn't offer the choice of a manual gearbox - something Porsche drivers take for granted. As smooth, fast and effective as BMW's eight-speed automatic is, it's just a little uninvolved in use. It's said that the less powerful Z4s will be offered with a manual gearbox at a later date.

The six-cylinder Z4 M40i is joined by two 2.0-litre, four-cylinder alternatives, both turbocharged. The BMW Z4 sDrive30i produces 254bhp and the Z4 sDrive20i has 194bhp. Claimed 0-62mph times are 5.4 and 6.6 seconds respectively. And while the sDrive20i might be nowhere near as muscular as the M40i, we found it surprisingly satisfying to drive. It has good throttle response for a turbocharged engine and still feels very quick.