THERE are two aspects to the TwinAir version of the Fiat 500C that are fascinating - the ground-breaking engine and the clever roof.

Fiat isn't joking saying the TwinAir powerplant is set to transform how drivers view petrol engines.

The result of a £300million investment, the technologically advanced low consumption 875cc two-cylinder is claimed to be the cleanest production petrol engine in the world.

Yet it is still a peppy individual that puts many a four-cylinder rival to shame.

And in the 500C, the engine offers an attractive means of downsizing so substantially reducing fuel consumption and exhaust emissions, but without sacrificing power or driver enjoyment.

The TwinAir engine weighs just 85kg so making the 500C responsive and fun to drive - helped by the neat and accurate five-speed manual gearbox.

Performance is further enhanced by a new generation of turbocharger that increases maximum torque as well as making it available at very low revs. This ensures the TwinAir engine is more flexible and responsive compared with normally aspirated units.

As with other 500s there's a wide-ranging options list and huge scope for owners to personalise their cars.

On top of that every TwinAir model features start/stop technology and a gear shift indicator to help drivers achieve the best economy figures possible.

In addition owners can specify Fiat's Blue&Me infotainment system that allows drivers to operate their music and phone via the car's steering wheel controls or with voice activation.

The convertible is not a full drop-top, but is fitted with a canvas roof that slides back leaving the doors and side frames intact.

It offers the advantage of being a moveable feast allowing you to fully enjoy the open air or set it at any position so you have as much or as little covering as required.

Opening and closing is a cinch as it simply requires you to push and hold a button at above your head and can be operated with the car travelling at speeds up to 30mph.

The roof can even be opened from outside of the car using the remote button on the key fob.

Traditionally the main drawback of a cabriolet with the roof down is the turbulence experienced by rear seat passengers as the protection afforded to the driver and front seat passenger by the windscreen is missing by the time the wind hits the back seats.

Thankfully Fiat have done something about this and in the 500C the roof can be adjusted so all the occupants are comfortable. There is even a tiny wind deflector on top of the windscreen and an optional rear wind deflector to fit behind the rear headrests.

Fiat's little car offers the sort of equipment levels normally the preserve of much larger cars. Pop, Lounge and Sport models all feature remote central locking, electric front windows and door mirrors.

Lounge spec adds parking sensors, chrome trim, parking sensors, front foglights, painted mirrors and 15-inch alloy wheels.

There's an extensive list of options and accessories including a blackboard-style dash panel, leather upholstery, Bluetooth, decals and panel stickers.

The 500C feels solid and stable on the road thanks to its solid roof pillars and rigid structure so there's little convertible-style shake, rattle or roll.

On what laughingly passes for a modern road network these days the ride can get a bit choppy on rougher surfaces but not unbearably so.