The outgoing BMW Z4, like the Z3 before it, was widely considered to be merely an expensive "sporty" car -- a Miata for well-off college coeds. But a full redesign for the 2009 BMW Z4 moves the car into the rarefied realm of true luxury/performance roadsters. The new Z4 is significantly more refined, there's a little more room inside and it now boasts a power-folding hardtop. It's more expensive, too, but that's to be expected with the advent of the retractable hardtop and a more luxurious interior. At $45,000-50,000 to start, the Z4 now goes head-to-head with well-established rivals like the Mercedes-Benz SLK-Class and the Porsche Boxster.

The Z4 mostly delivers when it comes to performance, the exception being its artificial-feeling electric power steering, and it adds a level of sophistication that few small convertibles can match. The base sDrive 30i comes with a capable inline-6 that's good for 255 hp, while the sDrive35i ups the ante with a 300-hp twin-turbocharged inline-6 that gets the roadster from zero to 60 in an estimated 5 seconds flat -- about as quick as last year's hard-core M version of the Z4. You can also get an all-new seven-speed dual-clutch automated manual transmission on the sDrive35i that's similar to the M3's "M DCT" gearbox.

The latest Z4 is about 6 inches longer and 350 pounds heavier than before. Visually, the car is stunning. There's even a hint of the classic BMW 507 from the 1950s if you look closely at the front end treatment. The power-retractable hardtop also adds a whole new dimension to the car. Owners still get the al fresco driving experience of a convertible, but now they can seal up the car with the hardtop when the noise, wind and/or temperature get to be too much. The Z4's cabin is also more elegant than it used to be, with better materials and greater attention to detail. BMW's controversial iDrive interface system is available on the Z4 for the first time, and thankfully it benefits from the substantial revisions that BMW has applied for '09. It's much easier to use than before.

From a value standpoint, vehicles like the Audi TT and upcoming Nissan 370Z roadster are less expensive, but the Z4's higher price gets you a lot more car. Mercedes-Benz's competitively priced SLK-Class remains a viable contender, but the new Z4 eclipses it in some ways. Porsche's Boxster ragtop and Cayman coupe are more dynamically involving, and Chevrolet's Corvette convertible delivers big V8 power, but they can't match the versatility of the Z4's retractable hardtop. Overall, the 2009 BMW Z4's combination of sophistication, luxury and performance makes it a compelling new entrant in this entertaining segment.

The 2009 BMW Z4 is a convertible with a retractable hardtop. Two versions are offered -- base sDrive30i and the more powerful sDrive35i. The main distinction between the two cars is in the engine bay, although each comes with slightly different levels of standard equipment. The base sDrive30i model includes 17-inch wheels with run-flat tires, a CD audio system with satellite radio preparation and an auxiliary input jack, a leather-wrapped steering wheel, dynamic cruise control and rain-sensing wipers. The sDrive35i adds niceties like leather seating, automatic climate control and aluminum interior trim.

There are several notable option packages. The Premium package includes leather and automatic climate control for the 30i model, power seats with driver-side memory, an auto-dimming rearview mirror, interior ambient lighting, Bluetooth and BMW Assist. The Cold Weather package includes headlight washers, a heated steering wheel, heated seats and a ski bag pass-through from the trunk. The Premium Sound package includes a high-end audio system plus a six-CD changer and an iPod jack. An Ivory White Leather package gives you exactly what it sounds like and also includes special wood trim and 10-way-adjustable sport seats. Finally, the Sport package includes 18-inch wheels with performance tires, adaptive suspension dampers, sport seats and a higher top speed thanks to a recalibrated electronic limiter.

Many of these options are available separately, but a few stand-alone options that are not included in packages are keyless ignition/entry, a hard-drive-based navigation system with a pop-up screen and music storage, parking sensors and HD radio.

The rear-wheel-drive 2009 BMW Z4 offers two engines -- one for each trim level. The base sDrive30i comes with a naturally aspirated 3.0-liter inline-6 that makes 255 hp and 220 pound-feet of torque. The sDrive35i receives BMW's ubiquitous twin-turbocharged inline-6 that's rated at 300 hp and 300 lb-ft of torque. Both cars come standard with a six-speed manual transmission. A seven-speed dual clutch automated manual is optional only on the sDrive35i. A six-speed automatic is optional on the non-turbo model.

BMW says the twin-turbo version of the Z4 can run from zero to 60 in 5 seconds flat, while the base model should lag roughly a second behind.

Side impact airbags, antilock brakes with brake assist, stability control and traction control are standard on the 2009 Z4. The roof is made of aluminum and incorporates a support system that helps protect occupants in case of a rollover accident. To provide protection in the event of a top-down rollover, there is a steel hoop behind each seat.

Even the base 2009 BMW Z4 sDrive30i is an entertaining drive thanks to its willing and preternaturally smooth 255-hp inline-6. The twin-turbocharged sDrive35i is better yet, offering up authoritative yet refined acceleration with no perceptible turbo lag. The snarky exhaust note only adds to the fun and gets angrier as the revs climb. The new dual-clutch automated manual transmission delivers quick and smooth shifts in manual mode, yet it doesn't lurch in parking lot situations, and gently easing into the throttle doesn't result in a sudden snap. In terms of handling and steering, BMW's latest roadster is sporty enough for most, but its reflexes and communication with the driver are lackluster when compared to those of Porsche's Boxster and Cayman. The main culprit here is the electric power steering system, which is largely devoid of the feel and feedback we expect in BMW products.

The 2009 BMW's Z4's cabin is considerably more upscale than its rather Spartan predecessor's. High-quality materials abound, and diverse shapes and exquisite surfaces combine to create a premium environment. Thankfully, BMW didn't forget about practicality along the way. There's a small storage area behind the seats that works well for purses or backpacks as well as a moderately sized pass-through that effectively expands trunk space to accommodate long items like skis or golf clubs. The new iDrive system is also worth mentioning, as it's much less cumbersome to use than previous iterations.

The hardtop does eat into storage space when folded -- there's a respectable 11 cubic feet with the top up, but only 6 with the top down. The folding top is power-operated and takes only about 20 seconds to retract.