BMW’s new Z4 has one job to do and it needs to do it right. The target is none other than the best-handling two-seat open sports car in the world, as defined by us, as defined by virtually everyone else on the planet, as grudgingly defined by BMW itself: the Porsche 718 Boxster. Naturally there will be lower-powered examples of the Z4 to help cover a wider area of the market than Porsche can hope to, but its launch model, the Z4 M40i tested here, is undoubtedly a shot across the bows of the good ship Stuttgart.

And whatever you think about the new Z4’s appearance (the internet forums are ablaze with disagreement on the subject), a quick glance at the tech specs for the M40i reveals that BMW has already bloodied the Boxster’s nose by fitting its protagonist with a six-cylinder engine. Sure, it’s turbocharged, just as the Porsche 718’s flat-four lump is, but the straight-six layout is far more melodious, whether you’re rumbling through the city with the roof down or screaming up the Jebel Jais Mountain Road with abandon. If the Z4’s engine was down on performance, you’d forgive it because of the wondrous noise it makes, but it’s not; it is a serious powerplant, producing 335bhp at the top end and, more usefully for everyday driving, a monster 500Nm of torque — with just 1,600rpm on the snazzy looking digitally rendered rev counter. The 0-100kph time of 4.6 seconds is identical to that of the Boxster GTS, though the Z4 is heavier and down 25 horsepower.

 

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The weight of the Z4 is partly down to BMW’s wish to make the most rigid open-topped car it has ever released and must also be affected by the huge standard specification of the M40i in particular. Along with the large engine up front, there’s adaptive damping, variable ratio steering, M Sport brakes and an active, electronically-controlled rear differential. The only transmission option is an eight-speed automatic, which has been updated considerably, but remains nigh-on perfect in operation. Leave it to its own devices and it is smooth and sensible in its gear changes and selection, aiming for higher ratios to rely on the engine’s considerable low-speed torque in a bid to save fuel. That is until you switch the car into Sport or Sport Plus modes. The latter in particular is significantly more aggressive in its settings than in previous BMWs (new 8 Series Coupe aside) and the gearbox calibration changes to one in which the lowest gear it can get away with is chosen, meaning you’re using the top of the rev band more often.

That driving mode also alters the damping, steering and throttle response, as we’re used to in BMW’s cars, but the largest change comes from the M-developed rear differential. In Sport Plus mode, this alters its remit from a stabilising influence to one that actively encourages the rear of the car to rotate as you enter a corner,  giving the Z4 a deliciously agile and adjustable stance into and out of a curve. In tighter bends, the variable steering contributes to the pointy sensation as you get turned in and, in the dry at least, there’s huge grip from the mixed size tyres. Being picky, we could say that the steering doesn’t have quite enough feedback, and we also wonder how much of that is down to the too-thick steering wheel rim.

Nonetheless, while the Boxster may still have the edge in terms of handling delicacy, the Z4 M40i remains an engaging and fun thing to drive — eclipsing its rather floppy predecessor. One thing the Z4 does particularly well is absorb bumps, regardless of driving mode. That’s despite the fact that it corners flat with tightly controlled body movements, no matter how hard you drive it. And, even when you are pushing on, it never feels edgy or nervous in its responses, making it an easy car to drive quickly, regardless of the conditions. Sure, you can feel the differential doing its thing when you’re exiting a wet junction in a hurry, but the electronics are very quick to act without it feeling like the engine is bogging down.

 

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Obviously, while BMW is targeting Porsche for the Z4’s handling prowess, not all roadster buyers care about such things. So, does it also get the basics right? Well, the new fabric roof looks good when up and can be specified in one of two colours, but it’s not as quiet nor secure as the old folding hardtop — and it could do with a more attractive cover over the folded roof, too. Clearly, all this has been done to keep weight down, plus the new hood lowers the centre  of gravity and needs less space to stow away. Hold the button down and it takes only 10 seconds to silently fold, and this can be done at speeds of up to 50kph if needs be.

Roof down, the cabin is blusterier than you might expect from something with a BMW badge on its bonnet, especially at speeds approaching 100kph. You’ll find it’s necessary to raise the side windows and fit the plastic wind breaker behind if you want to keep an expensive hairdo intact, for example… The cabin itself is a lovely place to be, with gorgeous leather-trimmed sports seats in a variety of colour options, an unassuming but attractive layout and, of course, BMW’s latest digital dashboard setup, featuring two large high-res screens — one for the instruments, another, a touchscreen, to control everything. We approve of the simple climate control switchgear and it, like every other button in the car, is perfectly damped and tactile to touch.

So, while the BMW Z4’s goal to take on the mighty Porsche 718 Boxster’s chassis may be a serious challenge for the newcomer, it has plenty more up its sleeve to tempt roadster buyers its way. They’ve never had it so good.