Sporting BMWs may have been inseparably associated with six cylinder engines down the years but the key powerplants on offer in this 'G29'-series Z4 line-up squirt fuel into the quartet of cylinders boasted by a TwinPower Turbo 2.0-litre unit that's offered in two states of tune. It's the 197hp sDrive20i variant that I tried, but this engine is also available in a 258hp state of tune in the alternative sDrive30i variant. You can talk to your dealer about a manual version of the base sDrive 20i, but otherwise, all Z4 variants come fitted with an 8-speed Steptronic Sport auto gearbox with gearshift paddles. Rest to 62mph in the '20i' takes 6.6s en route to 149mph.
You're probably going to want to pay extra for adaptive damping. The way the suspension interacts with the steering, the throttle and the differential is key to the way this car responds dynamically, so proactive use of the provided drive modes is crucial if you're pressing on. Do that and you'll find that this car lacks the razor-sharp steering responses of a rival Porsche 718 Boxster but the helm is quick and accurate, which in combination with superb front-end traction means that corners can be attacked with surprising confidence. Which is the kind of driving experience you'd want a proper roadster to be able to deliver. Is this one 'fun'? Well it can be - and that's a big step forward in Z4 development.
Brand loyalists will immediately recognise this as a BMW Z car - and it's not just down to the classic long-bonnet / short-roof format and the famous kidney badge on the grille. It's a shape certainly more arresting in reality than on the printed page, but one that you can't help feeling has been developed around its shared platform rather than with free-flowing stylistic expression. We should talk about the fabric roof, since that's a major change over the previous 'G89'-series Z4 with its metal folding top. It folds or erects in just ten seconds - the previous model's rather awkward display of metallic origami took almost twice as long to complete - and can be operated when travelling at speeds of up to 31mph.
Inside, you get the nicest and classiest interior you'll find in any small roadster on sale; if anything, it's almost too sophisticated for what's supposed to be a back-to-basics sports car. Most of the fixtures and fittings are lifted from BMW's luxury saloons, including the 10.25-inch centre-dash and instrument binnacle screens that make up the Bavarian brand's sophisticated 'Live Cockpit Professional' package. Apart from that, what strikes you most is the roominess of this cabin, which is one of the things that makes this car feel so everyday-usable. Out back, there's a decently-sized 281-litre boot.
The phrase 'affordable roadster' is a relative one in this case, given that even this least expensive sDrive20i variant with 197hp was priced from launch at around £37,000. That's with the paddleshift 8-speed auto gearbox that most Z4s have to have; for this base version, there's also the option of manual transmission if you want to save a fraction and involve yourself in the driving experience a touch more. Around 70% of Z4 buyers are expected to go for this sDrive20i derivative, with the remainder of sales split between the two more powerful auto-only models that make up the rest of the range.
On to rivals that compete directly with this sDrive20i variant. The most obvious competitor to what's on offer here is Audi's TT Roadster in base 40TFSI 194hp guise, which at first glance looks quite a lot cheaper, costing from around £33,500 - around £3,500 less than this directly comparable Z4 sDrive20i. BMW though, thinks that much of that difference would be eradicated if you equipped the Audi to match a Z4's level of spec. Perhaps. We'd be less inclined to consider the other direct option, the Mercedes SLC 200, which offers 184hp and in this form costs around £2,000 less than a Z4 sDrive20i. You might like the Merc if you retain an affection for the kind of metal-folding roof that the Z4 has now rejected. Otherwise though, the SLC's a rather aging design and, in comparison to this BMW, much less practical and somewhat unrewarding to drive.
Let's get to the stats. Regardless of your choice between four cylinder auto models - either this sDrive20i or the sDrive30i - you're looking at up to 38.7mpg and up to 138g/km of CO2. These very creditable readings actually compare extremely well to the rival Audi TT, though the fairly small plastic fuel tank's relatively small size - 52-litres - rather disguises the fact. In theory, a touring range of up to around 500 miles is possible.
Across the range, various 'EfficientDynamics' technologies are used to keep running costs in check. There's an engine 'Auto Start-Stop' system, as you would expect. And at highway speeds, the cruise control can seamlessly de-couple the engine from the transmission to reduce friction and consequently save fuel. Of course the driver will also need to do his or her part. The figures we've just quoted assume that the car is being run in the 'Drive Performance Control' system's most frugal 'ECO PRO' mode. In this setting, the air conditioning and power steering only work when required to save energy. Optimised aerodynamics obviously make a significant difference to economy too. BMW has developed what it calls 'Air Breathers' and 'Air Curtains', these devices respectively located behind and ahead of the front wheel arches, their purpose being to reduce turbulence - and therefore drag - in the area around the front wheels.
So what's been delivered here? A Porsche Boxster-beater? Not really. That might be what the magazines wanted but I'm not sure that likely owners are that bothered by such a comparison. This isn't the uncompromised driver's machine that its Porsche rival can be, but it gets close enough to that benchmark for many likely owners to start prioritising the lower pricing, nicer cabin and stronger standards of safety that you get with this Munich model.
BMW has been building roadsters for over 80 years - and it shows with this third generation design, a car that's matured extremely well, slowly and methodically developing into an all-rounder that's tough to beat. It's annoying though, that you have to spend so much more to get the Adaptive M suspension we think this car really needs for the completion of its ride and handling package. What it all means is that though the Z4 might not be the first car you look at when choosing a sports roadster, look at it you must. It's now just too good not to.