If you're set on getting a BMW Z4 and want one that's quick and forgiving, the 30i stands out on paper as the best candidate. It's cheaper and less hardcore than the M40i, plus with 258hp it also has a decent output advantage over the entry-level 20i. Clothed in M Sport trim, the 30i talks the talk, too - but walking? Well, BMW has invited us to find out on the trick combination of corners, camber and undulation you meet when driving on the North Wessex Downs.
Because this car costs from £42,445 it is impossible not to draw a direct comparison with the entry-level 718 Boxster, which costs £3.3k more - a difference that's unlikely to dissuade anyone in the roadster market from considering it. As soon as you slip into the Z4's cabin though it's clear that BMW's objectives were slightly different. The Porsche wraps around you like Lycra cycle wear; the Z4 does not - it's more obviously spacious and more obviously laid-back. The BMW's sporting pedigree is well hidden under a bushel made of its own usability.
Up ahead, the 30i's four-cylinder is essentially a more potent version of the 20i's, with its 2.0-litre capacity producing 258hp at 5,000rpm and 295lb ft of torque at 1,550rpm. There's enough muscle in the motor to sprint the 1,490kg 30i from 0-62mph in 5.4 seconds, so it's nine tenths off the pace provided by the M40i and within three tenths of the 2.0 Boxster. The 30i does, if you let it, also return a claimed 46.3 combined mpg as well, a figure which provides it with a handy USP right out of the gate.
The engine certainly feels capable from the get-go, its early surge of torque giving the Z4 the kind of big capacity amenability that its badge implies. Like other Z4s, this means the 30i places a premium on effortlessness - one that doesn't require any button pushing to access. The ride is a little frigid at times, sufficiently so for it to not quite fill out the B-road cruiser mould - but it's soft enough to not be impeded by the kind of surfacing imperfections that dot this part of England like moon craters.
Click through to Sport though and the adaptive dampers will constantly be informing you about whatever cracks and ridges are sailing by underneath. The quicker you go, the more condition improves - which means that you'll quickly find yourself heading into a bend at what feels like chancy speed. The grip you'll find once there have already become a familiar commodity of the CLAR-based Z4 on its wide tracks - although its worth noting that the 30i has just about enough power to unlock some rear-drive character traits that were missing entirely from the 20i. Turn in quickly and the back end can be brought into play with a fast-following open throttle, so it's a little more involving than the point and shoot nonchalance of the lesser Z4.
It doesn't sound particularly good, though, with the exhaust apparently content to drone for much of the rev-band. There's volume from the pipes, it's just not sporty or at all encouraging. You rev the motor simply to keep up the performance, rather than to take any joy from the soundtrack - which does make the M40i's six-pot unique in the line-up for more than just its extra poke. At least the eight-speed gearbox is swift; not on par with Porsche's PDK, mind, but quick enough for the application - although you'll be wanting its manual mode if you want to keep the motor in its most productive rev range.
Wind things up though and the 30i's cracks do begin to appear. Lighter than the M40i it may very well be, but the its softer settings mean that the body control is noticeably worse and over successive bumps the damping, even Ultimately this means that the process of charging down a country lane does not come entirely naturally to the 30i - a shortcoming compounded by the uncommunicative steering. Where a Boxster asks to be driven harder and feels lighter on its toes than it is, the fast-driven Z4 pleads with you for mercy. The 330d we subsequently drove along the same route made a much better fist of it.
That the 30i prefers your effort to be in the region of seven tenths is a trait it shares with the 20i model - but because it's never quite relaxed enough to be thought a proper drop-top GT, it manages to be neither one thing nor the other. It doesn't come close to the Boxster at pace, yet can't pull away from it in the comfort stakes when everything slows down. Given the looks, the low rev tractability and all-round niceness there are still positives to takeaway from the 30i - but failing to deliver the kind of acute handling compromise that marks out its saloon cars is a notable blemish on an otherwise worthy report card.
SPECIFICATION - BMW Z4 30I M SPORT
Engine: 1,998cc, four-cyl turbo
Transmission: 8-speed automatic, rear-wheel drive
Power (hp): 258@5,000rpm
Torque (lb ft): 295@1,550pm
0-62mph: 5.4 seconds
Top speed: 155mph