► Updated BMW Z4 roadster driven
► Top M40i petrol tested
► Out on track and road
Funny one, the BMW Z4, an enigma among the Bavarian roll call. At its best (Z4M Coupe), it’s mixed forward-looking styling with hairy-chested driving dynamics; at its worst it’s been a bit soft around the middle, a boulevardier that prioritised pose over poise. Some great engines in a so-so chassis.
BMW has updated the car that’s been on sale since 2018 but even after all this time, it remains something of a mixed bag – great in certain situations, iffy in others.
New BMW Z4: what’s the story?
The latest Z4 (‘G29’, BMW model code fans) is the first BMW to be jointly designed by Toyota, a co-operative project with the new Supra. There’s been some criticism of this venture but the reality is that without it, the financials simply wouldn’t make sense for either Toyota or BMW to build this sort of niche vehicle. In a world swarming with SUVs, that would be a pity so the tie-up gets our vote.
While the two cars share the same essential components, there’s plenty of clear water between them. The Supra is available purely as a fixed-head coupe, but the BMW is differentiated as a sun-seeking soft-top.
Here we’re testing the top Z4 M40i variant. As part of the mid-life update, BMW scrapped the 30i engine option so now just two remain – this M40i and the 2.0-litre four-cylinder. The trim levels have also been simplified: the 20i is only available with M Sport.
In-keeping with range-topping Z4 tradition, the M40i is powered by a straight-six, a 336bhp evolution of the ‘B58’ engine as seen in the M140i/M240i and 340i/440i. It’s turbocharged but its throttle response has been sharpened by software controlling the wastegate, and benchmarked against the previous, naturally aspirated six-cylinder Porsche Boxster.
Matching its Stuttgart rival’s handling is a tough ask, though, and BMW has endeavoured to give the Z4 the best start in life by siting two thirds of the engine behind the front axle for a claimed 50:50 weight distribution – sports car holy grail – and making it both considerably wider in track (by nearly 100mm at the front) and shorter in wheelbase than the previous Z4.
Kerb weight is 1535kg for the M40i, and its 19-inch wheels are wrapped in identical Michelin Pilot Super Sports to those of the BMW M3/4, right down to the size and compound. Suspension is by MacPherson strut at the front, multi-link at the rear.
So the top version gets a straight-six. What about the rest of the range?
The top-dog Z4 M40i is supplemented by one lower-tier model, the sDrive 20i. It uses a 2.0-litre turbo four-cylinder petrol engine, with 196bhp in the 20i.
Despite early rumours of all-wheel-drive capability, all Z4 models are rear-wheel-drive, and all use an eight-speed auto torque converter gearbox (the previously available manual has been dropped from the options list).
Why a fabric roof instead of the previous Z4’s folding hard-top?
It’s lighter, it’s faster (taking around 10 seconds to go from rainswept to cosy, around half the time of the old tin-topped Z4), it lets in less noise on the move and it lowers the centre of gravity a touch.
More prosaically, it means you get the same luggage space whether the roof’s up or down, so you get a fixed 265-litre boot instead of the previous car’s 310-roof-up/180-roof-down compromise.
Does it feel like a proper sports car inside?
More like a plush saloon car. Fit and finish feel perfect, there’s storage space aplenty for plus-sized phones and coffees and there’s also a fully digital instrument cluster, as seen on the 3- and 8-series. The iDrive 7.0 is no longer the very latest in BMW infotainment, but to our eyes that’s no bad thing. It keeps the 10.25-inch touchscreen married to a rotary controller and also still benefits from the physical shortcut buttons below the screen. Cars like the BMW X1 are far poorer for dropping this set-up.
Comfy, then?
Very. Whether the roof’s up or down, refinement is quite something for a roadster. There’s very little flex in the Z4’s structure, and that rigidity is as much a boon for comfort as it is for agility, extra bracing giving the suspension a consistent basis to work from.
Elbow propped on the door’s comfy armrest, back supported by the plump seats, it’s a soothing mode of travel. That said, driving the car on rougher UK roads, we’ve found the ride a little busy. While it absorbs big bumps well, it never quite settles down at a cruise, which is a shame as otherwise this is a fine long-distance car.
And a pretty unique one these days. The Audi TT Roadster is on its way out, the Porsche Boxster is going all-electric, the Mercedes SLC died eons ago. For the cliched wind-in-your-hair moment, the ICE Z4 is now an outlier.
And when you’re not in the mood to cruise?
First things first, it’s certainly quick enough, and the straight-six emits a reasonably tuneful burbly bellow (albeit one that’s artificially enhanced a little through the speakers, and punctuated by synthetic-sounding pops and crackles on the overrun in Sport mode, which quickly become tiresome). It’s a more evocative sound than the four-cylinder Porsche 718, but not necessarily one to make your hairs stand on end.
Throttle response is indeed sharp, and the engine’s powerband is flexible. The torque-converter gearbox doesn’t have the same whip-crack shift feel as a dual-clutch, but it’s well calibrated and has been programmed to downshift earlier when it senses you’re driving quickly.
Unlike the Z4 20i, the M40i gets adaptive dampers as standard (they’re optional on the four-pot car), along with uprated brakes and an electronically controlled locking diff (essentially a scaled-down version of that used in the BMW M5).
The way the steering, dampers and diff interact is key to the Z4’s dynamics. Brake hard and the front dampers’ rates change to resist dive, turn the wheel and the outside front shock stiffens while the other three adjust accordingly for the sharpest possible turn-in, and the suspension’s balance front to rear is manipulated on the fly for optimum agility.
‘You can’t divide steering, differential and dampers; they all interact,’ says driving dynamics engineer Florian Dietrich. ‘All four dampers’ compression and rebound rates adapt within 20 milliseconds, taking into account corner speed, steering angle, how fast you’ve turned the wheel, and more. And differently according to drive mode.’
As is the wont of modern BMWs, switchable driving modes for steering, dampers, gearbox and engine response ramp up through Comfort, Sport and Sport +, but there’s a more marked difference in feel between each than ever. In the latter two, the M40i is really quite tail-happy; begin to squeeze the throttle with some lock on and you feel it immediately tighten its line; tread a little more firmly and the rear quickly scooches round into mild oversteer.
Its sudden transition is characteristic of a short wheelbase, but it’s not unsafe, or intimidating; just a little more keen to play than you might expect, like an excited puppy. Keep your foot in and the diff quickly finds traction and the Z4 is very stable overall. It feels as if the diff has been programmed to create a little light initial oversteer in the Z4’s sportier driving modes to make it feel exciting at low speeds, but its keenness to wag its tail actually makes it feel a little clumsy on first acquaintance.
Despite the trick chassis and drivetrain tech, overall the Z4 feels more like an undemanding cruiser than a spine-tingling sports car. Subjectively, it doesn’t thrill at all speeds like a Boxster, but out-cossets the likes of the Mercedes SLC and Audi TT Roadster with superb refinement and ease of use. You’d happily live with a Z4 all year round.
We also tested the Z4 on track at Estoril, the superb former Grand Prix circuit in Portugal, and it acquitted itself very well. It’s stable under braking and keen to change direction, courtesy of the short wheelbase – which also makes it quite lively on the limit (though not alarmingly so) – you need to react quickly and work at the steering to get a quick lap time out of the M40i.
Verdict
Roadsters are an increasingly rare breed these days, and for BMW to have made the call to invest in the field is cause for celebration, even if it needed the JV with Toyota to make it a realistic prospect.
However, there’s a niggling feeling that it’s still a car best enjoyed at a cruise with an arm propped on the door in the sunshine rather than setting an early alarm to make the most of a favourite road. That might simply be a reflection of the Z4’s target market, and if that was the car’s internal brief it’s excelled. Despite its trick dampers and racecar track widths, it’s the BMW Z4’s refinement and comfort that leave more of a lasting impression than its capacity to thrill.
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