2008 Mercedes-Benz SLR McLaren Roadster

This final collaboration between Mercedes-Benz and McLaren is, like the Coupe and 722 Edition that preceded it, a technological wonder. It shares the same carbon-fiber-reinforced-plastic bones and 617-horsepower, 5.5-liter supercharged V-8, but the Roadster's semi-automatic cloth top opens up an entirely new, more pleasurable dimension to the thrill of driving the wickedly fast two-seater.

Because the SLR tub is so stiff, no structures were added to match the Coupe's torsional rigidity and, except for a new, stronger tri-axial CFRP weave in several components, most revisions are above the beltline: new windshield frame, rear fenders, trunklid, doors, and A-pillars integrating steel tubes as part of a safety system including two non-retractable hoops, six airbags, and sophisticated traction control.

The chart says 0-to-62 mph in 3.8 seconds and 0-to-124 mph in 10.9 seconds (about the time it takes to raise or lower the semi-electronic top); it doesn't mention the basso profundo of the sidepipes or the supercharger's shrill shrieks, aural gratification that never lets up until, in the right conditions, the Roadster reaches 206 mph. Because of a slick autobahn, we saw "only" 170 mph but reconfirmed the SLR's high-speed stability and comfort, which was hardly diminished even when the top was stowed. At U.S cruising speeds, the open cabin was quiet enough to enjoy the Bose stereo.

We most enjoyed the 575 pound-feet of torque, which yanked the 4050-pound car from slumber to silly fast in less time than it took to realize how stupid this was on the slippery roads. Even though we didn't exercise it fully (hey, it costs about a half million dollars!), the Roadster felt just like an SLR-bloody fast and remarkably comfortable. Still it's neither pursang sports car nor luxury GT.

Complaints? Apexes are obscured by the hefty A-pillars, the steering is heavy at slow speeds and numb when it's needed, and the composite brakes, though extremely effective, are too touchy.

No, the SLR is most impressive when disassembled, when its ultratech components become object lessons in the methods and materials that put McLaren and Mercedes-Benz at the pinnacle of motorsport. The sum of those parts is, for public roads, not as rewarding.