The range starts with a choice of 194bhp and 255bhp 2.0-litre turbocharged petrol engines in the sDrive20i and sDrive30i variants respectively. Both engines pick up well from low revs and put down their power easily, and the 30i feels every bit as quick as the Audi TT Roadster 45 TFSI.
However, BMW pitches the Z4 as a sports car and that’s where the sDrive20i and 30i fail to shine. Drive enthusiastically and you start to notice that neither engine revs as freely as the Audi TT 's 2.0-litre petrols do. Nor do they sound as exciting, letting out a dreary, monotonous drone. Performance feels blunted further by the standard eight-speed automatic gearbox (unlike the TT there's no manual option). This fails to respond eagerly when you put your foot down and doesn’t shift as snappily as its rivals', although it does respond more promptly when you change gear manually.
The range-topping M40i is much better. When you plant your right foot on the accelerator pedal, its 335bhp 3.0-litre straight six responds with virtually no lag, pulling hard from low in the rev range, especially if you stick it in Sport mode and make the most of the manual gearchange paddles. It sounds much more invigorating than the four-cylinder engines, too, with a smooth, free-revving nature that even the Porsche Boxster can’t match. And, while you’re still limited to an automatic gearbox, BMW’s eight-speeder is quick to respond, especially when changing down a gear for quick overtaking. Beefier M Sport brakes also help instil confidence when taking on country roads, while its bespoke electronically controlled limited-slip differential increases traction in corners.
Sadly, the improved handling touted by BMW never really materialises. If you stick with the standard passive suspension, the Z4 feels better tuned for motorway cruising than canyon carving, and can feel rather wayward over B-road bumps. Don’t expect much smoothness from the 10mm-lower M Sport suspension, though, and the M40i has 19in alloy wheels as standard, which doesn’t help ride comfort at all. The optional adaptive dampers make a big difference, but; while the Comfort mode is noticeably softer than the standard set-up (although it can still crash over harsh road imperfections), the Sport mode might be rather too firm for some tastes. Unfortunately, the Z4 never feels as planted to the road as the TT.
Then there's the steering. A lack of initial weight around the straight-ahead makes it feel somewhat disconnected, and it pulls from side to side under hard braking. To compound its disjointed nature, if you turn it beyond 45 degrees the speed of response suddenly ramps up, making it harder to place on the road.
The brakes continue this theme. They stop you quickly but are hard to modulate, with little resistance at the top of the pedal's travel. This makes it difficult to drive smoothly, particularly at slow speeds. All these niggles conspire to make it very hard to truly enjoy the Z4's rear-wheel-drive layout and, if you want something that feels altogether more fun and nimble to drive, the TT Roadster is a better all-rounder.
It's not all bad, though; its relative lack of wind and road noise on the motorway is another positive – well, with the roof up. Open it (something that takes around 12sec with the push of a button) and there's more buffeting than you'll experience in the TT, even when the optional wind deflector is in place .