THE BMW ‘Z’ may have won hearts over the past dozen years, but respect eluded the Z3 and first Z4, despite their fundamental differences.

The less said about the crass Z3 the better – mad M Roadster and M Coupe excepted – but its sharper and shapelier Z4 successor was massively better.

However, perhaps it was the electric power steering, rock-hard ride, polarising design or the fact that the Porsche Boxster did almost everything better, but BMW just couldn’t crack the big time with the Z4 either.

Enter the second-generation Z4 – or Z5, as it really should be called. Codenamed E89, the re-born Munich roadster is a clean-sheet redesign, with a larger body and roomier cabin, while even bigger things going on both below as well as above.

For instance, in comes BMW’s iDrive menu interface, the M-DCT seven-speed double-clutch gearbox on the torturously titled sDrive35i tested here, and – most tellingly – a folding hardtop.

This is a ragtop to riches story.

You don’t have to be a jockey to realise that a bigger body, more gadgets and a 30kg roof where a cloth-covered roof previously sufficed all add weight.

Mass is anathema to a sports car: against the preceding E85 Z4, this one’s up to 195kg lardier. It’s like having two adult males travelling with you at all times.

BMW is chasing the Mercedes-Benz SLK (luxury sport grand tourer) rather than the Boxster (sport GT), while the rumoured Z2 lightweight two-seater will be BMW’s Mazda MX-5-style sports roadster when/if it arrives.

Z4 has changed direction. The promise, then, is rapid, refined and comfortable SLK slayer but with BMW athleticism and attitude.

So is the Z4 sdrive35i a ‘best-of-both-worlds’ experience?

Starting from the top, BMW says the electro-hydraulic retractable roof, which takes a tardy 20 seconds to deploy, improves everything – security obviously, but also all-round vision, since there are raised glass areas. Cheers to that, BMW!

Acid test: With the roof down, little wind buffeting spoils the peace, no matter where the side windows are, and the heaters do a mighty fine job of keeping everything warm and cosy in colder conditions. Completely denuded – simple thanks to a single button – and the cabin remains commendably calm, even at three-figure velocities.

Unfortunately, while noise levels are much lower than before when the roof is erected, the newcomer can still be quite droney, depending on speed and road surface. Hands-free phone conversations can mean raised voices, strained ears and hoarse throats.

But the interior is one of BMW’s best anyway, blitzing the competition with a nod to the forgotten left-hand drive-only Z9 luxo cruiser of a decade ago. This fact alone helps to justify the sDrive35i’s Boxster-baiting pricing.

Fold yourself down inside – some muscular alacrity with the hardtop in place does come in handy here – and you’re sitting low and snug, as if your posterior is positioned directly on the rear axle. The view ahead is like that from the base of a long arrow so expansive is the bonnet out ahead. This feels like a cockpit in more ways that one.

Matching the interior architecture, the seats are first class, with excellent bolstering when you need it most through corners, and massive amounts of adjustability for all.

Our test car’s beautifully stitched leather upper-dashboard area, accompanied by classy wood inlays, optional Nappa leather and suede-like seat and door card inserts, catapulted the Z4 cabin to Maserati-like standards. Divine.

God herself lurked in details such as the three-spoke steering wheel, quartet of exquisite climate control settings that are among the easiest we have ever experienced, metallic door handles and hinged lower door pockets.

Of course, this is a two-seater drop top, so there is little real storage space in the cabin, but thoughtfully, BMW provides a netted and carpeted shelf area behind the seats for soft items (including a fabric roof once upon a time …), a lidded box in the rear firewall and a coat hook hanging from the apex of the triangular safety roll hoops. They’re useful only if your names are Ken and Barbie.

Top marks to the latest iDrive, which is simple to use after a brief acclimatisation, and a fast and accurate satellite navigation system. Better still, seductive French and Spanish language options to the android-English means that the Z4 can now teach you another tongue, literally on the go.

“Por favor, no me pregunten por mi hombría!” would have been a useful cry out to the driver behind waving her pinky finger on one occasion.

However, with so much effort exercised in the cabin, it is curious that BMW didn’t bother with the audio controls and actual instrument dials, which are crystal clear to locate and use but look like they’re out of a base 116i. Disappointing.

And what an eyesore the pair of exposed roof-folding mechanisms are, standing out through a pair of ceiling cut-out squares like beacons. We thought the roof lining had somehow fallen away.

The boot is also a concern. While it is 50 litres larger than before – 310 litres with the roof up (enough for a pair of full-size golf bags using the through-load system, BMW claims) – it shrinks to just 180 litres with the hardtop housed down inside, trailing the old Z4 by 80 litres. Not very efficient or dynamic having a hefty roof inside, is it BMW?

By golly though, doesn’t the latest flagship Z4 (for now) fly regardless, thanks to the sDrive35i’s supernaturally sensational 3.0-litre twin-turbo direct petrol injection inline six-cylinder engine.

The 225kW of power at 5800rpm and 400Nm of torque from just 1300 to 5000rpm are the winning numbers to jot down here.

Mated to BMW’s seven-speed dual-clutch automated transmission (a considerable $3500 option over the standard six-speeder), this 2979cc twin-turbo canon blasts the drop top beyond 100km/h in a 911 Cabriolet equalling 5.1 seconds, trailing the Boxster S PDK by just 0.1s.

Actually, ‘blasts’ is misleading, because everything about the way this twin-turbo Z4 moves is methadone smooth.

In normal Drive, one is instantly whisked away with almost magic carpet-ride levels of refinement as the dual-clutch gearbox executes seamless ratio changes to match.

But the stubby gear stick is a pain, particularly for novices, because a side thumb-press is necessary before ‘Reverse’ or ‘Drive’ can be engaged, and in hurried moments you can be left with the lever in the right slot but the car going nowhere.

Then there are the sequential shift options. BMW fits a pair of wheel-mounted paddle shifts where a pull takes you up a ratio and a rather awkward thumb push slots you down. Our example felt sticky and unintuitive, so we ended up resorting to the easier lever with its paddle mirroring back-for-up and forward-for-down shift motions.

Select ‘DS’ for Drive Sport, and everything is more forceful yet virtually as effortless as when left in Normal Drive.

In DS, the Z4 displays an addict’s zeal for speed, bounding forward at any velocity in a twin-turbocharged thrust of activity, while keeping remarkably surefooted. And the dual-clutch trannie always feels like it is in the right gear.

Yet our Z4 ranged between 12.5 and 14L/100km in mostly city and urban driving conditions – a great achievement with such a large performance well to draw upon, and keeping in mind that our sports car fantasies were well and truly satiated by the time we handed back the key. More sedate driving would undoubtedly improve the economy.

BMW says front-to-rear weight distribution is better than before, and this is immediately evident in the sDrive35i’s exceptional roadholding abilities.

Point that well-endowed nose into a turn and around you will go, slow or fast, with a weighty precision, if not a whole lot of tactile feedback from the muted Servotronic electric steering. Not even a hint of a shake or a tail wag is present at higher velocities, either, with all the electronic driver aids variously pulling their strings to take away any impending sting or spin.

Safeties in place, the previous Z4’s cornering twitchiness has been polished away. All the driver need do is hold on to that fat little steering wheel and go.

But there isn’t quite the lightweight chuckability of a Porsche Cayman, and this – more than anything else – cements the Z4’s place as a monumentally capable grand tourer, albeit one with a heady handling and cornering compulsion.

The driver can progressively dampen the stability and traction levels and quicken steering and throttle responses too by pressing down from Normal to either the Sport or Sport-Plus modes via the Dynamic Drive Control (DDC) toggle switch next to the gear lever.

This brings back some of the more visceral acceleration and handling characteristics of the previous Z4 3.0i models, allowing for the tyre-smoking, as well as controllable, oversteering antics that buyers of rear-drive roadsters surely expect from their rides.

Beware that driver skill also needs to be in maximum plus-mode when using the BMW’s most extreme DDC setting with the ESP extinguished in slippery and/or dangerous conditions.

Frankly we weren’t game enough to try, but we hear opposite lock antics are just a few button presses away we can say though that you do have a guardian angel watching in the form of superb body control, combined with powerful and progressive brakes.

In the end, though, selecting DS was more than enough to engage us while, like a Siren singing, the exhaust egged us on for more. Shifting through the gears, the twin-turbo six sounds like Barry White gargling mouthwash through a phase vocoder.

But what might be even sweeter music to your ears is the realisation that the new car’s suspension possesses none of the old Z4’s jarring sharpness.

Larger bumps and dodgy road surfaces will still illicit the odd thump so there is no mistaking this for an old French car, but the big-six roadster’s ride is no longer purgatory.

At more than $120,000, the Z4 flagship pulls away from its predecessor’s Audi TT play area and heads straight into the boxing ring against the base Boxster and Benz SLK 350.

So BMW hasn’t been stingy with the standard equipment. The entry $86,200 sDrive23i includes twin front and side/thorax airbags, a pair of fixed rollover hoops, electronic stability and traction controls, anti-lock brakes, cornering brake control, electronic differential lock, cruise control with brake function, run-flat tyres with pressure indicator, automatic wipers and headlights, front and rear parking sensors, leather upholstery, DDC, bi-Xenon headlights with washers, heated seats, climate-control air-conditioning, power windows/mirrors, heated rear glass, and a trip computer.

The sDrive35i adds BMW’s Comfort access keyless entry/start system with remote roof operation, sports seats, adaptive headlights, high-beam assist, 18-inch alloy wheels with 225/40 and 255/35-section tyres and anti-dazzle exterior mirrors.

And then there’s that chainsaw symphony twin-turbo weapon, allowing the Z4 to pussyfoot around with the softer SLK yet play hardball with the Boxster. Ultimately, the sDrive35i positions itself between the two.

But going the folding hardtop route is a soft option too far for a BMW roadster against the Porsche, with the resulting weight and boot space compromises undermining our faith in the company’s judgment. Particularly as there is still so much road noise to contend with on some surfaces.

Nevertheless, we suggest that you really take the time to get to know the sDrive35i before buying an SLK or TT – the design, for instance, is full of intricate details that, like the driving experience itself, improve with familiarity.

The latest BMW roadster deserves the respect that the showy but shallow Z3 and flawed but still quite fab first Z4 never found.

For this fact alone, and as we said back at the car’s launch in May, BMW should have called it the Z5.