Drop the BMW Z4 roadster's power-retractable top (photos)

We grabbed the keys to the most powerful variant of BMW's Z4, the 2013 sDrive35is.

The 2013 BMW Z4 sDrive35is' proportions are classic roadster: long hood, short tail, low, and lean.

Under the hood you'll find a 3.0L turbocharged inline six-cylinder engine. Twin-scroll technology reduces lag, while still delivering 335 horsepower.

I spent pretty much every mile of my testing period with the Z4 with its top stowed away. This is the best way to experience a roadster.

The power-retractable roof raises or lowers in about 20 seconds. I was able to activate the roof even at low, parking-lot speeds.

Subjectively, I'm not as much a fan of the Z4's silhouette with the roof raised, but the curved dome does make extra space for tall drivers' heads.

Our tester was equipped with optional 19-inch alloy wheels.

The 332 pound-feet of torque exits through the rear wheels after passing through a seven-speed DCT automatic transmission. This is the only gearbox available at this trim level.

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.

Roadsters aren't known for their practicality, and the Z4 is no exception. The roof intrudes into the trunk when is retracted, leaving just enough space for a carry-on bag or two.

With the roof in its upright position, a few more cubic feet of trunk space is made available, but it's awkwardly laid out and the quarters are still fairly cramped.

The BMW's interior is luxurious without being too plush.

All of the controls -- the shifter, the steering-wheel buttons, the HVAC buttons -- are easy to reach, wrapping around the driver's seat. The iDrive controller is placed a bit far back and it's awkward to reach, but you won't want to go fiddling with it when corner carving anyway.

The leather seats are swathed in beige leather. The driver's seat is power-adjustable and both buckets feature heated surfaces.

The center console is home to the odd BMW shifter, the iDrive controller, and the Drive Experience Selector. There's also an awkward cupholder that intrudes into the passenger's leg room, but that can be quickly removed with a tug.

The iDrive system has a smooth learning curve and is fairly easy to understand. I particularly like the shortcuts to the various infotainment modes.

Instrumentation is a simple bi-gauge setup: speedo on the left, tach on the right. Between them is a small monochromatic LCD trip computer. Although the Z4 features BMW's EfficientDynamics regenerative braking, the roadster does not feature a brake-regen gauge.

Dual-zone, automatic climate control on a two-seat roadster seems like overkill, but the Z4 has it. The Z4 also has a dedicated button on the steering wheel to change the recirculation mode. Why? We don't know.

Rising up from the dashboard is the ultrawide BMW infotainment screen. The resolution is fantastic and the interface is easy to navigate.

The optional navigation system features gorgeous topographic maps when zoomed out.

BMW Online services allow users to search Google Local for destinations and businesses that may not be in the vehicle's database.

Destinations found online include a small Google Maps preview of their locations. However, navigation is still handled by the onboard iDrive system, not the Google Maps navigation you'll find on your smartphone.

Available audio sources include Bluetooth for hands-free calling and audio streaming, a 3.5mm analog auxiliary input, CD/DVD playback, satellite radio, and AM/FM radio with HD Radio decoding. There's also a bit of hard-drive space dedicated to ripping music from audio CDs.

Check out our full review of the 2013 BMW Z4 sDrive35is for more details and driving impressions.