This marginal weight gain pays dividends when it comes to performance, too. As with the Coupé, the Roadster’s power is sent to its rear wheels by a turbocharged 1.5-litre three-cylinder petrol engine (related to that you’ll find in the £16,000 Mini One), while an electric motor does the same for the fronts. From a standstill, the Roadster will hit 62mph in 4.6sec - just 0.2sec slower than the Coupé.
And while the petrol engine is no more powerful than it was back in 2014, at 228bhp and 236lb ft, updated battery technology means the motor now produces an additional 12bhp.
What's it like?
Aside from the infinite head room and additional wind buffeting that’s common to any open-top sports car, you’d really have a hard time differentiating the Roadster from the Coupé. This is both good and bad, because for every pro that’s carried over, so too are a couple of cons.
Let’s deal with those negatives first. The ride, for instance, suffers from the same choppiness that mars the hardtop’s manners at low speed – behaviour that’s only really ironed out when travelling at pace on a smooth motorway.
Then there are the brakes, or more specifically the brake pedal. Its positioning is fine - in fact, all of the Roadster’s controls are located in the sort of easy-to-access places you’d expect them to be in a driver-focused sports car - but its action is vague and numb and never really leaves you with a clear idea of how much travel you should be using to slow the car down. That's not ideal when you’re fast approaching a sharp hairpin high up a Spanish mountainside.
And when, having slowed the car down, you get to that hairpin and turn in to clip the apex, you’ll expose what is perhaps the i8's most frustrating shortcoming: understeer. It’s by no means the “oh my God, I’m going to spear straight into the Armco barrier” sort of understeer - far from it. Backing off or pinning the throttle to pivot the rear around will indeed remedy things nicely. It’s just that the struggle the 215/45-section front tyres often have to endure to find purchase is enough to make you question just how at ease the Roadster really is with being a sports car.
Adapt your driving style with this in mind, though, and you’ll find there’s still plenty of fun to be had. Lower your entry speed, trail brake into a corner to force the front end to turn and then pin the throttle on exit, relying on the electric motor’s instant torque to help plug the gap left by the engine, and the i8 will prove it’s still a properly quick point-to-point machine.
It’s under these sorts of conditions that you’ll begin to notice the i8’s strengths: through fast, flowing corners, its body remains impressively flat and composed; the weighty steering rack is quick enough to lend the i8 a front end that feels responsive without being twitchy or nervous; and the two power sources combine not only to provide impressive responsiveness under throttle, but also a fairly serious turn of pace.