I love the simplicity of a good roadster. There is a purity to the direct connection between driver and vehicle, with no extra seats, no gadgetry, and so few distractions from the singular purpose of driving quickly. The lack of a roof means that you're in the environment, not just driving through it, enhancing the connection with the road. Lots of people like cars, but what roadster fans are really in love with is driving.
The 2013 BMW Z4 sDrive35is is not so simple. It's packed to the gills with tech. It's not quite at a Mercedes-Benz SL level of bloat and complexity, but it's also no spartan Mazda Miata. The dashboard is dominated by a large screen, gadgets, bells, and whistles. Overhead, there's the power-retractable hardtop that must weigh more than a ragtop. And while it makes up for the increased weight of the power roof and power leather seats with a turbocharged brute of an engine, it also sends its power through a computer-controlled dual-clutch automatic transmission and steers with electronic assistance that adds another layer of separation between the driver and the drive.
But there is such a thing as being too much of a purist and, despite these subjective critiques of the Z4, the sDrive35is model is still a pretty sweet ride and a proper roadster. The proportions are just right -- whether you love or hate BMW's visually complex style -- the performance is all there, the complexity that underlies that performance vanishes once you start chaining together corners, and the tech is fairly easy to master. More importantly, it simply begs to be driven with the top down.
The Z4's power-retractable hardtop hides away and returns in about 20 seconds at the touch of a button. Sources say that the roadster needs to be stopped to activate the roof, but I was able to drop the top with the vehicle moving at parking-lot speeds.
The metal and glass of the roof and rear skylight intrude into the trunk when stowed, leaving only enough storage space for a pair of carry-on bags. With the roof raised, there is actually a reasonable amount of space that can be reclaimed, but because I consider driving a roadster with the roof up to be automotive blasphemy, let's just say that you won't be making a Costco run in this red toy, relegating it to second-car status.
A fabric roof would weigh less and take up less space, but there are, of course, advantages to a hard-roofed roadster: The vehicle is slightly more protected from thieves. The roof is less easily damaged. The cabin can be better insulated against rain, cold, and wind noise at the touch of a button.
You're also better insulated from the exhaust note, which can barely be heard with the hardtop in place. With the top down, you can enjoy the burble of the sDrive35is power train's exhaust, the whoosh of the induction, the wind around your ears.
With the top up, the Z4's curved roofline affords a bit of extra headroom for tall drivers, but even at 5' 9", I felt a bit claustrophobic after hours of open-air motoring. (You'll want to check out Brian's video for a taller driver's opinion.) From outside the car, the Z4's design also seems better-proportioned without the roofline's awkward hunch.
The power train
Beneath the Z4's endlessly long aluminum hood is the heart of the sDrive35is' power train: a 3.0-liter BMW TwinPower Turbo inline six-cylinder, which we've seen before spinning the wheels of BMW's 135is and 335is.
Output is stated at 335 horsepower and 332 pound-feet of torque thanks to the usual suspects of a twin-scroll turbocharger, variable valve control, and direct-injection technologies. The sDrive35is has a neat trick called Overboost that allows the turbocharged engine to temporarily increase its boost pressure under full throttle, bumping up the peak torque to 369 pound-feet for a short burst of acceleration. The driver doesn't need to do anything but plant the accelerator pedal to activate this feature.
Speaking of pedals, the Z4 sDrive35is can only be had with two of them -- sorry, fans of clutch pedals -- as it is not available with a standard transmission option. The only gearbox available is BMW's seven-speed dual-clutch automatic transmission with paddle shifters. This transmission features sport and manual programs, the latter being controlled with either steering-wheel-mounted paddle shifters or the oddball BMW shift lever.
Power exiting the transmission heads to the rear wheels via a traditional open differential. No limited-slip diff, no torque-vectoring tech here. The Z4 is, however, capable of using its rear brakes as a sort of electronic differential to improve stability and traction.
Like many modern Bimmers, the Z4 uses a brake energy regeneration system to convert a bit of braking force into electrical power to charge the 12V battery, eliminating the need for an alternator and its parasitic drag and increasing fuel efficiency. The vehicle also makes use of electronic power steering to eliminate the need for a hydraulic power-steering pump to the same end.
The EPA estimates that the 2013 Z4 sDrive35is will average 19 mpg in this configuration. That's the combined average, which breaks down to 17 mpg in the city and 24 mpg on the hwy. I averaged about 20.4 mpg according to the Z4's trip computer, which was miraculous since I spent the week driving like an average BMW driver.
Z4 drivers have access to three Driving Experience modes with a rocker switch on the center console, but I didn't notice much difference between the Comfort, Sport, and Sport+ settings. The Driving Experience Control system adjusts the throttle response, the shift points of the gearbox, and -- when in Sport+ mode -- the characteristics of the DSC stability system. Were the Z4 equipped with the available adaptive suspension, the Driving Experience Control would also alter the roadster's dampers, but our tester was not so equipped, which probably explains why the Driving Experience modes felt so similar.
Fortunately, similar or not, the Z4's driving experience is a good one. With the deep burble of the sDrive35is' exhaust note urging me forward, the immediacy of the handling inspiring just a bit more daring, and the race car efficiency of the paddle-shifted gearbox, who could blame me for driving with a little extra zest? The Z4 is quick, but it also makes you feel awesome while sitting in the driver's seat.
The 335-horsepower Z4 is certainly not lacking in the power department. Thrust delivery is part linear, predictable, and intense -- particularly when you occasionally feel the extra surge of torque when the Overboost kicks in. Thanks to the standard DCT, the power delivery is also seamless, with almost no interruption for shifts.