What is it?
The Z4 has changed. It’s become sportier – the old one, with its folding hardtop and cuddly dynamics, took aim mostly at the Mercedes SLK (now SLC). The new one has a fabric top, dropping the weight measurement and centre of gravity. It’s evidently having a pop at the Porsche 718, itself in a vulnerable position since the much-lamented departure of that old flat six.

To prove its sporting bent, we’re driving a Z4 with an M in its name. Well, a part-way M car, the Z4 M40i. It’s got a turbo six with 340bhp. Other engines are four-cylinders in the 30i and 20i.

Ah yes, sporty. Hello internet, the ’Ring time is comfortably under eight minutes. The Z4’s physical dimensions are good for hot laps. The wheelbase is shorter than before by a huge 20cm, for agility. The track is much wider, for grip. The body is a whole lot stiffer than the old Z4’s, and it’s light.

The front suspension, unlike other BMWs, mounts to a special aluminium subframe for precision. Those aren’t the only declarations of intent. The Z4 M40i’s tyres come from the M4. Its brakes are M-developed too. There’s an e-diff between the rear half-shafts. You get the gist.

You can thank Toyota for the existence of the Z4. Toyota wanted a new Supra but didn’t have a platform. BMW saw the roadster market softening and wasn’t sure if it could sell enough to justify replacing the Z4. But sharing could satisfy the spreadsheet-jockeys. BMW of course is one of the staunchest global holdouts for straight-six engines and rear drive, two articles of faith for a Supra.

What is it like on the road?
Six cylinders. Those two words take you a long way into the appeal of the M40i. It revs to 7,000rpm, and all the sensations – in the pull of it and the sound of it – say it’s pretty darned chuffed to be doing so. Use the paddles why don’t you.

And when you enjoy the engine’s generosity, the chassis can easily cope. As promised, there’s enormous grip, and the suspension keeps a vigilant eye on body roll and float. The steering is high geared – gets even more so on lock too – but it acts intuitively so you can always aim the car with lovely accuracy, and even small efforts will thread it into a tight bend with the immense forces those tyres can generate.

Only thing is, the steering doesn’t bring back a whole big lot of sensation from the front wheels. That job is left up to the back end. You feel the e-diff working as you lean onto the power, the rear half of the Z4 crouching down and neatly holding onto the edge of traction as it bleeds out of a bend.

The engineers say the handling target was the M2. I don’t think the Z4 is quite that transparent, but it’s that capable.

Unlike the M2, the Z4 M40i has adaptive dampers, so full-on recreational driving isn’t its only happy place. Even in the sport mode, where you get clearly sharper turn-in, the dampers allow the suspension to relax a certain amount on the straights. In comfort mode, things really become remarkably supple, rounding off most of what a broken surface throws at it.

So the Z4’s chassis relaxes nicely into commuting or long-haul work. And while you’re at it, the driver aids and headlamps are all you’d expect from modern German premium.

On the inside
The seats haven’t just been yanked out of a saloon. They’re bespoke to the Z4, and have electric bolsters to plug you solidly into the car whatever your girth.

Mouldings for the dash and door cards are also different from the rest of the BMW range, but, as with the 8 Series, maybe not different enough to make the Z4 feel really distinctive. It seems people want their BMW to be fully BMW-esque in all particulars.

So the iDrive, virtual instruments and the climate controls are ‘version 7.0’, exactly the same as all this year’s BMWs (X5, 8 Series, Z4, 3 Series) and beyond.

It’s an easy system to manipulate in most ways. Our fingers are less frustrated manipulating hardware buttons for climate, and an actual rotary controller and shortcut buttons for other stuff, than they are when jabbing at Audi’s new all-touchscreen system. And the BMW central screen is touch-sensitive now anyway.

But whatever was wrong with clear round dials? The rev-counter is an odd polygon, with red-on-red markings and a short needle. It’s absurdly hard to read, and this in a sports car.

A navigation diagram sits between the speedo and rev-counter, but if you know where you’re going you can’t reconfigure that real estate to show anything more useful. Yes I’ve banged on about the graphics of that cluster before, and familiarity has in no way bred content.

Folding hardtops were invented when soft tops were too easily penetrated by the weather and vandals with Stanley knives. These days a well-done fabric roof really is all you could want for coziness, and the yobs are too busily engaged in social-media bullying. Wearing a cloth cap does no harm to the Z4, and it usefully increases the boot size too.

Roof-up at motorway-speed-plus-VAT, there’s a mildly turbulent hiss of rushing air, but otherwise its insulation, warmth and general stormproofing are beyond serious reproach.

Spend 15 seconds pressing a button to lower the cloth but keep the windows up and the neat little between-the-rollhoops wind deflector in place. That way you can still enjoy the excellent stereo at big open-roof speeds. Even on a parky day there’d be no call for one of those airscarf gadgets.

Verdict
The Z4 has made a big step ahead. Mind you it kept, and improved, the best bit, the straight-six.

The new chassis is properly athletic, able to cover ground in a serious manner. We’d like to feel a bit more engaged with the steering though.

Still, there’s a lot to be said for the way it can relax out of a pants-on-fire style and behave with civility for daily use and long motorway hauls. It’s practical too.

Style matters in a roadster too. This one? You decide. We reckon many of you already have.