Space and practicality
As a two-seat convertible, the Z4 is fighting a losing game when it comes to spaciousness and family appeal. There's no back seats at all, although the front seats are excellent for adults of any size.
Storage is decent, with a caveat. The boot is 310 litres, which is actually on a par with many supermini hatchbacks, but only with the roof in place. Lower the roof and this space is slashed to just 180 litres as the roof folds into a part of the boot. This is pretty small by any standard, even smaller than the boot on any city car.
The folding metal roof does, though, bring enhanced security compared to the soft-top of old. Fabric roofs are vulnerable to opportunist thefts of valuables and belongings from the vehicle, but the tin top gives the convertible experience without this risk.
The Z4 was tested by EuroNCAP in 2015, after the facelift, and scored just three stars although that doesn't quite tell the whole story. A 69% rating in occupant safety wasn't as a result of poor crash performance – in fact very few areas rated below 'good' – but the car has no autonomous emergency braking system.
Engines
There's two basic engines available on the Z4, although they're in different states of tune depending on the model. Both are 'Twin Power' turbocharged petrol engines.
The lower-capacity version is a 2.0-litre, four-cylinder unit. This is fitted to the base model sDrive18i car, producing 154hp. With a 0-60mph sprint time of 7.7s (7.9s for the automatic) and a top speed of 137mph, performance is adequate, but bear in mind that this is the most economical Z4, at 41.5mpg combined and 159g/km CO2.
A 181hp version of the same engine is fitted to the sDrive20i. Official emissions and economy statistics don't change from the sDrive18i, but it's around a second quicker to 60mph at 6.7s and the top speed moves up to 146mph.
The third version of this engine is in the sDrive28i. In this application it produces 241hp, which is enough to slash the acceleration figures to a rather brisk 5.5s 0-60mph (or 5.3s for the automatic) and invoke the classic BMW 155mph top speed limiter. The official fuel economy and emissions numbers are again 41.5mpg and 159g/km CO2, but it's not likely that this will be as frugal in real life as its lower-powered siblings.
The second engine is the 3.0-litre, twin turbocharged straight six, also available in two states of tune. As fitted to the sDrive35i model, it produces 302hp, springing to 60mph in dead-on 5 seconds (4.9s for the automatic), with the same 155mph limited top speed as the sDrive28i. Fuel economy takes a bit of a nosedive though, to just 31mpg, with emissions up at 211g/km.
Not to be confused with the sDrive35i, the top model is the sDrive35is. Here, that straight six engine produces 335hp and can only be paired with a seven-speed dual-clutch automatic, good for a 0-60mph time of 4.6s. Top speed is also limited to 155mph and the economy and emissions figures are as per the sDrive35i model.
Running costs
How the Z4 harms your pocket depends on whether you prefer the straight six engine or can make do with the four-cylinder option.
Although not truly bad, the Z4 only manages 41.5mpg in sDrive18i, 20i and 28i forms, and it's likely that this will be worse in real, day-to-day driving. The insurance group is similarly on the high side, with the sDrive18i sitting in group 34. The CO2 rating even for the entry level car gives it a £500 year one penalty for road tax too.
Move to the six-cylinder sDrive35i and sDrive35is and these costs skyrocket. First year VED is £1,200 - and if you get too careless with the specifications and send it over £40,000, you'll find yourself another £310 a year out of pocket. Insurance group is 42 or 43 and fuel economy is down to a best-case scenario of 31mpg.
Although not based on any other BMW, there's quite a few components derived from other models in the range, particularly older 3 Series cars. For the most part this makes servicing and repair fairly reasonable and it's a generally reliable car – but always be prepared for something more specific to the car failing and needing a costly replacement. Some consumables are pricey too.