When the 4C was first displayed as a concept car at the 2011 Geneva motor show, we wondered if Lotus might have had a hand in its construction.

It hadn’t, but you can imagine, before a carbonfibre tub had been confirmed, why we might have thought that the Norfolk-based company had donated some DNA: composite construction aside, the 4C is a mid-engined lightweight car in the Lotus tradition.

Nic Cackett

Nic Cackett

Road tester
The rear deck is heavier than that of an Elise but it does have similar trait: lift it in the wet and water drips into the boot

With two seats and a modestly sized 1742cc four-cylinder engine mounted transversely and driving the rear wheels, the 4C has a dry weight of just 940kg in this Spider form.

In fact, full of fluids but otherwise empty, the 4C Spider tipped our scales at a respectable 1080kg – a full 120kg less than the Lotus Exige we weighed in 2013.

Look to the 4C’s carbonfibre construction if you’re after reasons why it’s so much lighter than a similarly sized Lotus. Yes, the engine is also smaller than the Lotus’s V6 but its four-pot is turbocharged and also bears the weight burden of being mated to a six-speed dual-clutch automatic transmission rather than a manual gearbox. Under 1100kg is an impressive figure.

Top 5 Sports cars

Find an Autocar car review

Explore the Alfa Romeo range

Driven this week

In converting the 4C from a fixed-head car into a convertible, Alfa Romeo has perhaps inevitably made the Spider a little heavier than its coupé sibling: Alfa’s official figures have the 4C Coupé at 45kg lighter.

The Spider’s carbonfibre monocoque is itself unchanged, but there’s an additional aluminium roll hoop beneath what Alfa Romeo calls the ‘halo’ behind the passenger compartment, the windscreen surround is new (and fashioned from carbonfibre) and there’s a high-strength steel cross member in the engine bay to enhance body stiffness. Then there’s the weight of the insulated hood, too.

Those elements aside, the 4C Spider’s mechanical make-up is much the same as that of the coupé version. The engine produces the same 237bhp and 258lb ft of torque, and suspension is by double wishbones at the front but MacPherson struts at the rear. (Porsche’s Cayman uses struts, too, so there is no shame in that in itself.)

Save money on your car insurance

Compare quotesCompare insurance quotes

Find an Autocar car review

Explore the Alfa Romeo range

Driven this week