Mercedes S-Class

There's no doubt Mercedes' seven-speed box noticeably improves high-speed refinement, plus performance and economy. It's just a shame the electronics don't cope so well with everyday traffic, jerkily searching through the gears. Otherwise, this is an exceptionally smooth car.

There's a mountain bike propped up against the office wall which has 27 gears. This might seem a little bit excessive to those of us who were brought up on Sturmey-Archer three-speeds, but up a steep hill you'll be glad of the conserved energy and improved performance resulting from having the right ratio.

Mercedes had the same idea to make the most of its V8 powerplants, and is going 'seven up' with its new 7G automatic transmission. It's the first seven-speed gearbox to be fitted to a car, and is now standard on all 5.0-litre petrol non-AMG models.

Do the extra two ratios make that much difference? To find out, we drove the first 7G-equipped model to arrive in the UK - an S500L. Externally, there is no difference, and the only way to tell for sure is to select manual mode and look at the numbers on the dashboard display. But start taking note of the fuel economy or check the car's performance against a stopwatch, and the benefits are much clearer.

Official fuel consumption improves from 21.1mpg on the previous model to 24.8mpg, while the 0-60mph time drops by 0.3 second to 6.2 seconds. On a long trip of motorway and urban miles, we averaged 28.8mpg - which is exceptional for a vehicle with such performance and dimensions.

Move through the gears at normal pace and the shifts are almost imperceptible - much as you'd expect from a luxury model. On the motorway, the car slots into top gear, where 70mph equals a relaxed 1,700rpm, or 800rpm less than the outgoing version. Use the throttle lightly and it is fine, and the electronics cope well when the pedal gets buried in the carpet. But that's not to say it's perfect. Cruising along at half throttle, the gearbox is easily confused and can't decide on a suitable ratio. It will settle on one gear, then rapidly downchange two at once after only the merest squeeze of the accelerator. This results in rather jerky progress, which is at odds with the luxury feel of the big saloon. Indeed, it's enough to take the fizz out of the Merc's seven up...