What is it? The car with the cleanest internal combustion engine.
Unless you go electric, no car produces fewer CO2 emissions than this Ecodynamics version of the new Rio supermini - its 85g/km easily bettering any hybrid or eco diesel model on sale today.
It's powered by a 1.1-litre three-cylinder turbodiesel engine, with direct-injection, and a variable-vane turbo. Low weight (despite being bigger than the outgoing model, it weighs the same) and a long list of fuel-saving aids also help its efficiency.
The economy aids include engine stop-start, low-rolling-resistance tyres, longer gearing, an extended tailgate spoiler and a closed-off radiator grille.
However the real key is the 1.1 litre's pulling power, a stout 125lb ft arriving at an early 1500rpm and persisting through to 2750rpm. In other words, there's useful muscle here.
What's it like to drive? This Rio immediately sounds different with its quietly beating three-cylinder idle. It's a noise that's not unpleasant and stays that way when you rev it. The engine is quite an eager revver too, with the result that its performance feels stronger than its 14.9sec 0-62mph time suggests, and a whole lot stronger than you'd imagine a 1.1 diesel motor to be.
You don't need to use the smooth-moving six speed gearbox as much as you'd think to maintain a pace, and it will even pull sixth gear with reasonable conviction. True, this is no performance car, and the motor gets a bit noisy if you stretch it, but the Ecodynamics Rio is a lot more sprightly, and enjoyable, than its name suggests.
Then there's the economy, or at least the promise of it. This car returns 88.3mpg on the combined cycle, and while official numbers like these are increasingly unrealistic, it's likely that this car will nevertheless return excellent fuel economy figures, even if they rarely scale the 80mpg-plus promised.
The Rio's handling and ride are less characterful than its engine, although the smaller wheels and tyres of this eco version allow it to deal more effectively with small bumps.
It tackles corners tidily, but you may miss the pleasure that Ford's Fiesta serves on a twisty road. On the plus side, the cabin is roomy – this is a bigger supermini than average – and the Rio is decently civilised at speed.
Should I buy one? It's not the cheapest supermini at £11,895, but this particular Rio is a mechanically sophisticated car.
You'll pay no road tax, no London congestion charge and enjoy the potential for spectacular fuel consumption in a car that's thoroughly up-to-date, well-equipped (with plenty of safety kit) and comes with a strong seven-year, 100,000-mile warranty. For many, that will prove an irresistible combination.
