2018 Mercedes-AMG GT Roadster and GT C Roadster First Ride

I'm standing in the hostile, bristling desert outside Las Vegas with Mercedes-AMG boss Tobias Moers and taking in a prototype of his new, topless AMG GT C. There's also a routine GT Roadster and a C63 S Cabriolet that have been thrown in for good measure. The zaftig nature of the original AMG GT's backside has appealed to me on a guttural design level, but the C variant redefinesbadonk. Call me Sir Mix-a-Lot. The GT C's butt is vented, and it looks fab.

Those of you with keen eyes will note that we've seen this look elsewhere; the upcoming GT R and the GT C share the same wide body kit (2.2 inches thicker, rear fender to rear fender). Turns out the vents—two vertical slits behind the rear wheels to remove hot air from the brakes and a horizontal one to vent heat from the GT R's racy exhaust pipes—are only for show on the GT C. But what a show. I couldn't take my eyes off the GT C's glutes.

Confused by the alphabet soup? Here's a primer. There are, for now, four versions of this AMG sports car the GT, the GT S, the GT C, and the GT R. There are also five power levels (more on that later). Complicating things further, the C variant is launching only as a Roadster, but a hardtop GT C will be available in the future. The C does not stand for Convertible or Cabriolet, despite the insistence of some erroneous press reports. In Mercedes-speak, Roadster refers to a two-seat convertible, whereas Cabriolet is a softtop with a back seat. Got it? So what does the C in GT C stand for? Clydesdales, apparently, and 550 of them.

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It's about all that horsepower. All AMG GTs use the now-ubiquitous hand-assembled 4.0-liter dry-sump twin-turbo V-8 also known as M178. For you engine code nerds out there, the generally torquier versions of this motor are found in the C63 and new E63 and are labeled M177. In the AMG GT coupe, the M178 pumps out 456 hp and 443 lb-ft of torque. Confusingly, AMG GT Roadster's power figures are 469 hp and 465 lb-ft of torque. Why the difference between the two cars with the same name? I don't know. If I had to guess, AMG wants as much bandwidth for this product as possible. The lower the power, the lower the price point. Given that equation, the AMG GT S—the machine that won our Best Driver's Car honors in 2015—makes 503 hp and 479 lb-ft of torque. The GT C Roadster's engine is good for 550 hp and 502 lb-ft of torque, and all that twist is impressively available from 1,900 to 5750 rpm. The hardtop-only "Beast of the Green Hell" GT R generates 577 hp and 516 lb-ft of torque

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This jaunt around southwestern Nevada is the latest in a long-running series of ride-alongs with Moers. He drives, and I ask questions. The first thing he tells me is that the AMG GT Roadster is a super early prototype, and one of the first to roll off the assembly line. Moers says it has a different steering setup than the final production version. He also repeatedly apologizes for its copious rattles and squeaks.

How did the GT Roadster feel from the passenger seat? Like a not-so-healthy preproduction AMG GT with the top cut off. As for that top, Moers caught me looking at my watch as I raised and lowered it, which is something you can do at speeds up to 30 mph. "Only takes 10 seconds," he says. "Nine by my watch," I respond. "Ten," he snaps back. This is a guy who folds his arms in disgust at red lights.

As for the GT C Roadster, it felt impressive. It was quick and powerful, sure, though that's nothing new. There's a raft of other go-fast goodies, too—namely, the active air management system lifted directly from the big dog GT R. There are vertical louvers (think venetian blinds) mounted below the front grille. When extra cooling isn't needed, they're closed to reduce drag and increase fuel economy. Get that mighty engine hot enough, and in less than a second the louvers crack open.

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I couldn't feel the louvers working, but I sure did notice the rear-wheel steering. In a word, the GT C feels dartier than the GT S. The car seems to change direction more quickly and fluidly than its fixed-rear-wheel counterpart. This is especially impressive because a wider rear track and fatter back tires usually mean more grip but not increased dexterity. Also borrowed from the forthcoming GT R is an electronically locking differential that should further help to put power down and change the car's direction. The seven-speed dual-clutch has reconfigured software and a few new physical gears: a shorter first gear for improved acceleration, and taller seventh gear and final drive for better response when cruising.

In short, the dark gray GT C we only got to experience from the wrong seat is emotional, loud, quick, and sexy. It will be available for individuals with a high net worth to purchase by fall 2017. What a little monster.