CHALLENGING COASTAL roads and large Mercedes coupes traditionally go together like the yips and a title-deciding 18thhole putt. But the E400 Coupe is keeping its composure on the roads that lead from Barcelona towards the Pyrenees. Sport Plus mode selected, air suspension flexing its muscles, the Merc’s body deftly follows every steering input like a choreographed dancer. The composure is maintained at surprisingly high speed thanks to the standard 4Matic allwheel drive; more power is going to the front wheels than you’d experience with an xDrive BMW, but it’s still a rear-biased feel. When understeer creeps in, you just feed in throttle and ping out of the bend. This is no out-and-out sports car, but for a four-seat coupe that should cosset and pamper first and foremost, the broad grin on my face is unexpected.

Until 2009, the equivalent car was the CLK. It was a C-Class chassis wearing a coupe bodyshell, its design clearly derivative of the E-Class saloon. CLK became E-Class Coupe for 2009, but the C-Class hand-me-downs continued. The new model, the filling in a C- and S-Class coupe sandwich, is almost astonishingly logical in comparison. Called E-Class Coupe, it is based on the E-Class saloon.

That explains the substantial increase in dimensions versus the outgoing model, with a length of 4826mm (+123mm), width of 1860mm (+74mm) and a height of 1430mm (+33mm). The wheelbase is actually shorter than the E saloon’s (2939mm to 2873mm), but there’s still ample room for four full-size adults (and there are only four seats), and space for 450 litres of golf clubs. It’s a lovely cabin too, the architecture again derived from the saloon, its organically curvaceous lines lifted by bespoke jewellery including the six jet-engine-style air vents and open-pore wood treatments. You’ll need to upgrade from standard and quite convincing Artico manmade ‘leather’ to the real thing, though, and the widescreen cockpit - two 12.3-inch screens lined up flush together to create a digital instrument binnacle and infotainment screen - is a further £495 stretch away, or almost £2k for E220d/ E300 models which don’t come with the bellsand-whistles Comand Online infotainment.

Yet fundamentally this feels a special, relaxing place to while away miles. For such a familiar concept, the E-Class Coupe has surprisingly few rivals. The ageing BMW 6-series is similar, but in 640i guise is £9k more expensive than a £50,775 E400 4Matic, doesn’t get all-wheel drive and, claims the man from Merc, delivers 14mm less rear legroom. And because the E-Class Coupe is available with both four-cylinder petrol and diesel engines, it starts from £40,135 where the entry-level BMW 640i is £59,535.

Notwithstanding the ugly quarter light in the rear side glass (best disguised with tints), even basic models look desirable, all UK cars coming with the beefier AMG Line styling upgrade and 19-inch alloys. Shame the four-pots feel like cold mathematical equations to get company-car drivers behind the wheel (the E220d promises 71mpg and 106g/km). They spoil the coupe’s character, thrashing angrily as hot-hatch power attempts to make more than 1600kg of metal get out of an actual hot hatch’s way.

The E400 4Matic is so much nicer. The performance is far from exceptional, but the 3.0-litre turbocharged V6 makes 328bhp and 354lb ft for more than ample acceleration, and sings with a richly refined and suitably subtle exhaust note. Pressing the over-fizzy throttle in Sport Plus mode is like opening a shaken can of Coke, but mix and match the settings, dial it back a bit and you’re watching the swan gliding effortlessly over the surface instead of sitting with the galley slaves rowing the E220d and E300. Later, the E350d and range-topping E43 AMG will offer different V6 twists.

Specified on air suspension, lowered 15mm compared with the saloon, and with the gorgeous 20-inch alloys a gnaw-your-armoff tempting £595, our test car’s ride lulls with a plush elasticity on admittedly quite smooth Spanish test routes, its fast variable-rate steering minimising work at the wheel and soon feeling natural, even if you’re more aware of the changing ratio than in its rivals.

The general hush of the cabin is occasionally spoilt by some noticeable wind noise on our early car, and the occasional random thunk from the usually silky nine-speed automatic, but typically you feel more relaxed at journey’s end than you do on climbing aboard. Exactly what you want from a big luxurious coupe. That the E400 can pick apart a challenging road without breaking sweat makes it all the more appealing.