First Drive: Mercedes-Benz G Class G63 5dr Tip Auto

As we know from so many other AMG cars, this twin-turbo 5.5-litre V8 engine is a marvel. It's not even fazed by hauling the G-class. Put it up against a weight of 2.6 tonnes and a Cd of 0.53, and it still manages to produce serious performance.

At any revs, a jab of the throttle calls up a satisfying forward lunge. Epic gusts of NASCAR rumble issue from the four side-exhaust tips below the doors.

For a vehicle that can actually get itself into fairly hostile off-road territory, this is impressive - albeit by no means unique these days.

Gallery: the Mercedes G63 AMG

That, m'lud, concludes the case for the defence. Every other characteristic of the G63 lies on the prosecution side.

AMG's normal practice is to take Mercedes models - cars that are already highly competent in handling and braking - and then give the chassis a thorough overhaul to take it to an even higher level. In the case of the G-Class, it's a vehicle that was launched 33 years ago, and was never designed for on-road duty. Plus, because the chassis consists of solid axles, there's very little AMG can do to change it.

So the G63 is ridiculously bad at cornering. It has pathetically little grip and tragically vague steering. Really, you arrive at the first corner and it feels like someone has buttered the road. You flail away with huge armfuls of steering input, understeer madly, then feel the ESP juddering into action.

Braking, especially from speed, doesn't feel too stable either.

Never mind, you'll soon be stopping to steady your nerves. You'll have to, because the tank will be empty. I saw 11mpg.

Despite the G-Class's Titanic weight, it's not that big or comfy inside. This latest facelift has added contemporary sat nav and communications, but it's a tissue-thin gesture. The driver's seat doesn't go very far back, and if it did there'd only be enough rear legroom for kids. Because of all unsprung ironmongery down below, the ride's shuddery. The shoebox shape kicks up a load of wind noise.

So let's put it in some sort of Mercedes perspective. You're paying the price of a V12 S-class. You're getting something with the performance of a V6 SLK but the cornering of a Smart. It has the space of an A-class, and the consumption and refinement of an Actros truck. It's all wrong.

AMG does an ML off-roader that does a far better job in every measurable way. But people buy these G-Class cars because they are cool. Well I can't agree. Come on people, what's so cool about something so dumb?