2003 BMW M3 Convertible vs. 2003 Mercedes CLK55 AMG Cabriolet

Even though AMG and M cars are inspired by Mercedes-Benz and BMW racing activities, the CLK55 Cabriolet and M3 Convertible aren't the smallest, fastest, raciest versions. You might consider them "lifestyle" models-assuming your lifestyle requires 333 horsepower or more.

Although it's reasonable to expect limited luggage capacity in sports-car packages like the M Roadster or SLK32, the M3 and CLK55 are relatively large cars. Yet each barely holds a weekend's worth of bags in the trunk with the top down. Further, the rear seats are supposed to hold two adults, but they don't accomplish it too well. So don't plan any long trips involving four up, plus luggage, in either machine. However, some might argue that the utility and function of an M or AMG lie in their powerful engines, not in something so pedestrian as cargo capacity. Here's where these cars go from totally impractical to downright logical, once you drive them on a mountain road on a sunny day-with the top down. Want to haul four people? Buy a sedan.

The M3's on-board entertainment system is a 3.2L/333-hp I-6 that pumps out a conservatively rated 262 lb-ft of torque. It features variable valve timing, plenty of forged steel, semi-dry sump lubrication, and a two-stage throttle blade system. The CLK55's 5.4L/342-hp V-8 boasts two more cylinders and a torque rating of 376 lb-ft. It has two spark plugs and three valves per cylinder (two intake/one exhaust). Add a high-flowing intake manifold and aggressive camshaft specs, and you've got a V-8 that carries a tune like a mid-'60s Corvette.

With nearly identical curb weights and horsepower, this pair runs comparable 0-60-mph times-5.02 sec for the M3 and 5.23 for the CLK55. The difference closes slightly at the end of the quarter mile, with the M3 recording a 13.63/103.76, while the CLK55 runs a respectable 13.74/104.44. MT test driver Chris Walton noted that the CLK55 produces lots of wheelspin off the line, while the M3 stays better hooked up. The CLK's five-speed automatic transmission performs nearly perfect shifts, thanks to the Touch Shift manumatic gear selector. However, Walton found it harder to drive the M3 once it gets rolling because it's easy to hit the 8000-rpm rev limiter on the 1-2 and 2-3 shifts of the six-speed manual transmission. A possible solution is BMW's optional Sequential Manual Gearbox ($2400). Derived from BMW's F1 cars, the system uses a manual transmission, an automated clutch (no pedal to push), and steering-wheel-mounted shift paddles. Despite being down 114 lb-ft of torque, the M3 won our acceleration test by a hair, thanks to better traction and even more aggressive gearing.

Both share suspension upgrades with their M and AMG coupe brothers, including higher-rate springs, sport-calibrated shocks, thicker anti-roll bars, and stiffer bushings. On the handling course, the M3 emerged the victor, running through the slalom at 67.07 mph, while the CLK55 cabrio trailed at 64.32 mph. Walton labeled the M3 as more athletic with its 18-in. tires, quick steering, and knife-edged handling limit. The CLK is more predictable, but understeers more, too, largely due to its relatively small 225/45ZR17 front tires. Both maintain a firm ride quality, yet within tolerable levels for those long trips. On bumpy surfaces, the M3's chassis demonstrates noticeably more cowl shake than the CLK55-a quality not befitting a car of this caliber.

Each has large and able brakes, the CLK55 sporting 13.2-in. front and 11.8-in. rear rotors, while the M3 has 12.8-in. fronts and 12.9-in. rears. Both produced near record-stopping distances from 60 mph, with the Mercedes coming to a halt in 116 ft and the BMW stopping 2.0 ft shorter at 114. Fade was almost undetectable over miles of spirited mountain driving.