Bentley is showing its fastest-ever open car at the Detroit motor show. The Continental GTC Speed is powered by a 616bhp version of its evergreen 6-litre W12 motor, enough says Bentley to push the 2.5 tonne car through the air at 202mph.

Other improvements over the previous GTC Speed include the provision of an eight-speed transmission, said to be the main factor in a 15 per cent fuel consumption improvement, although a combined figure of just 19mpg seems stuck in another era. As with previous Speed models, the new GTC comes with lowered, stiffened suspension and a meatier feel to its Servotronic power steering.

Of course Bentley’s claimed top speed is, like those of all other convertibles, recorded with the roof in place. A few years ago I went to the Nardo test track to see if this car’s predecessor would hit the double ton with the roof down. It stopped short at 197mph, due to the convertible’s sub-optimal aero profile, but managed 204mph with the hood up. It would be interesting if academic to see whether the new GTC was the world’s first genuine four-seater capable of a genuine 200mph with the roof down.

The webcast will be live at 5.40pm GMT.