In BMW lore, the ‘iS’ nomenclature has always been reserved for special, sporty cars – models that don’t quite achieve the dizzying performance heights of the Bavarian auto maker’s hallowed ‘M’ cars, but are still licensed to thrill well beyond the level of the standard versions.

No surprise then that the ‘iS’ version of the Z4 has become something of a bone of contention. It’s certainly not a homologation special, created solely for the purposes of racing. But it also lacks the outright appeal that true sports cars harness.

Part of the reason is a lack of credibility – a problem created by BMW’s own focus on the Z4’s comfort and lifestyle, rather than traditional performance driving pleasure. Which is where the sDrive35iS comes in. This ‘iS’ derivative links extra muscle to various advanced attributes.

The most important aspect of the new sDrive35iS are healthy dollops of extra power and torque. Besides that additional urge, the  newcomer also gets BMW’s M Sports Package, which adds a number of enhancements, including special alloy wheels fitted with fatter rubber and a host of interior improvements.

Perhaps more importantly, the’ iS’ gets adaptive M Suspension and Drive Dynamic Control, as well as a sports version of BMW’s Dual Clutch Transmission, complete with shift paddles.

Drive Dynamic Control allows the throttle response, shift timing, stability control and steering feel to be varied between Normal, Sport and Sport Plus settings. The sportier the setting, the sharper the responses, and the more lenient the stability control.

The M Suspension lowers the Z4 by 10mm, and employs electronically controlled dampers that are individually adjustable, allowing the damping rate at each corner to be rapidly and continuously varied, depending on road conditions and driving style.

None of these changes is that obvious from the outside. Sure, the wheels are new, and the badges on the side confirm this Z4’s iS status, but the differences are pretty subtle.

Unique to the iS are a lower front bumper with larger air intakes and matt aluminium finishes, a revised rear bumper incorporating a diffuser and different tailpipe surrounds. But it’s still a big car in two-door roadster terms, and both the prowling nose and the short rear deck remain key identifiers.

Oh yes, and it still showcases a metal retractable roof instead of the simpler, lighter canvas hood of previous models.

The Z4’s design is very much an acquired taste. For me, its increase in girth and weight has robbed the two-seater of some of its aggression. Yes, it’s allowed a better packaged interior with improved ergonomics, and yes, the car still features a perfect 50:50 weight distribution. But it lacks the keen edge and honed looks of the first Z4.

That said, the lower stance and bigger wheels do add some visual muscle, and it certainly looks more hunkered down, and more aggressive, than the standard model. Also, given that this is a roadster, it’s at its most appealing with the roof stowed away.

Folding away the tin top provides a decent view of the cabin, which may have more room than the previous Z4, but can hardly be described as spacious. It’s a snug two-seater with not nearly enough storage for oddments, but excellent ergonomics put the driver very much in control of proceedings.

The retractable roof is raised and lowered in around 20 seconds, and still offers a reasonable 180 litres of boot space with the roof stowed. With the roof in place, that capacity increases to 310 litres, which should be enough for the ubiquitous golf bag. The bad news? There’s no spare wheel …

Since the’ iS’ is the flagship of the Z4 range, the interior appointments are comprehensive. The bells and whistles include automatic climate control, remote central locking, a superb sound system, satellite navigation, full leather upholstery and electrically operated sports seats.

Unique to the ‘iS’ version are subtle details like bespoke sill trims, aluminium carbon finishes and an anthracite roof lining.

The best part of the Z4 sDrive35iS is the engine. It’s a twin-turbo, 3,0-litre straight six, tweaked to deliver a wholesome 250kW of max power and 440Nm of torque. Even better, an overboost function increases the twist to a full 500Nm for short blasts.

That’s 25kW and 40Nm more than the normal sDrive35i, which provides a welcome boost to the Z4’s power-to-weight ratio. However, the standard DCT gearbox is something of a mixed blessing.

There’s no manual option, which seems silly. And while the DCT gearbox is swift and smooth – and offers an ego-stroking launch control function for perfect pullaways – it has to make do with silly push-pull paddles. Pull back, and you shift down. Push forward, and you shift up.

They’re painful to use and out of kilter with what the rest of the motor industry is doing: a left paddle for downshifts, and a right paddle for upshifts. That’s what the BMW M3 is equipped with, and even Porsche had to change from push-pull shifters to the dedicated paddles.

The rest is classic BMW: the gearbox transmits power to the rear wheels, while the 50:50 weight distribution promises poise and precision, especially with the adaptive suspension and lower ride height.

And it’s on the road that the Z4 package redeems itself. Certainly, the straight-line urge is prodigious, with the ESP working overtime to prevent wheelspin and optimise traction. The factory figures suggest a zero to 100km/h sprint time of 4,8 seconds, and a top speed limited to 250km/h.

Since the engine is turbocharged , there is almost no altitude-related power loss, and the Z4 feels every inch the powerful sports car when driven with vigour.

Pity the engine note is dulled by the turbo plumbing, despite some careful sonic tuning by BMW’s engineers. It just doesn’t sound as thrilling as a normally aspirated straight six, although there is a delightful pre-detonation ‘pop’ when shifting gears.

The other highlight of this Z4 is the handling. The suspension  feels much more convincing than the standard car’s, thanks to the tauter set-up and lower ride height. The electric power steering is still too wooden, but chassis feedback is direct and undiluted: this car tells you exactly what it’s doing.

Even in Sport mode, the stability control tends to intervene too much. Switch to Sport Plus, and progress is more fluid, although the risk of the rear stepping out is a real and frequently experienced one, albeit without any malice.

The Z4’s inherent poise, and its quick steering, make it easy to control, even at the limit. And besides, the DSC stability control still provides a safety net, but only when things get truly out of shape.

Of course, the Z4 can also be considered an effortless and versatile cruiser. It covers ground rapidly and confidently, with enough in the way of comfort to make long-distance trips a feasible proposition. Bring on the twisties of a mountain pass and it rises to the occasion with the vigour of a sports car.

The big question is who exactly will be buying the Z4 sDrive325iS? At R780 000-odd, depending on options, the BMW roadster finds itself in some serious sports car territory, with the likes of the Porsche Boxster S and the Audi TT-RS as tempting alternatives.

In sheer dynamic terms, the Z4 is right up there with the serious metal, but as far as perception goes, there’s still more hairdresser than racing driver in its profile. And that probably makes the Z4 sDrive35iS the most misunderstood car on this planet.

What you see, isn’t always what you get … DM

You can reach Deon Schoeman on [email protected]

KEY STATS

Engine
In-line six-cylinder, 2 979 cc, twin-turbocharged

Gearbox
Seven-speed DCT

Power
250 kW @ 5 900 rpm

Torque
440 Nm @ 1 500 rpm

0-100 km/h
4,8 sec

Top speed
250 km/h (governed)

Fuel consumption
13,8 l/100 km (tested)

CO₂ emissions
210 g/km

Retail price
R770 500 (before options)