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BMW i8 Roadster 2018 review

Autocar logo Autocar 30/04/2018 Greg Kable

BMW i8 Roadster 2018 review

BMW i8 Roadster 2018 review
© Autocar

What is it?

We’ve waited a long time for the BMW i8 Roadster.

First previewed at the Beijing motor show as the i8 Concept Spyder in 2012, it’s taken a full six years for the plug-in hybrid open-top to be offered in the UK. In that time, the car has undergone a significant amount of development. But, despite the long gestation, it hasn’t lost any of its original impact.

BMW i8 Roadster 2018 review © Autocar BMW i8 Roadster 2018 review

Its contemporary exterior design and advanced powertrain specification might be familiar, coming some three years after the launch of the i8 Coupé, but there are few cars at any price that can claim to make such a powerful visual and technical statement as this roadster.

If anything, the i8’s futuristic lines are further enhanced by the loss of its roof, most notably around the rear, which has gained added prominence on the roadster due to the appearance of two large buttresses in the place taken up by the liftback-style tailgate on the coupé. 

The roof, which consists of a large fabric panel and integrated header rails, opens automatically in 15 seconds at speeds up to 31mph. It boats near-silent full electric operation and stows vertically behind the two-seat cabin at the press of a button, nestling in a space-saving position between the rear bulkhead and mid-rear mounted combustion engine.

BMW i8 Roadster 2018 review © Autocar BMW i8 Roadster 2018 review

What is it like?

To accommodate the new soft top, BMW has modified the windscreen of the i8, providing it with a strengthened carbonfibre frame. The rear window, which doubles as a wind deflector, is also altered and can be closed or opened independently of the roof.

Further stylistic changes over the facelifted i8 Coupé that's set for UK delivery at the same time in June include the deletion of the rear side windows. They are replaced by new panels overlaid with aluminium-look trims with the word 'Roadster' on the side of the new buttresses.

BMW i8 Roadster 2018 review © Autocar BMW i8 Roadster 2018 review

In combination with further strengthening measures within the carbonfibre-reinforced plastic and aluminium structure and new frameless scissor-action doors, weight has increased by 60kg over the facelifted coupé at 1595kg.

Inside, the two-plus-two configuration of the fixed-roof i8 has given way to a two-seat layout, with the rear of the cabin altered to provide 92 litres of oddment space within three separate cubby holes in the rear bulkhead. It combines with the 88 litres of the rear-mounted luggage area to provide an overall 160 litres of stowage space.

The earlier dashboard design has also been lightly updated for the i8 Roadster and facelifted i8 Coupé. Among other subtle changes, the latest version of BMW’s iDrive system now offers either touch control on a free-standing 8.8in monitor or via a rotary dial on the middle console.

BMW i8 Roadster 2018 review © Autocar BMW i8 Roadster 2018 review

There are also new seats, an optional head-up display unit as well a range of new trim options, including carbonfibre trim elements for the dashboard and ceramic controls within the centre console.

One key change in the powertrain is an increase in output from the front-mounted electric motor. The unit, which was produced in-house, now delivers 12bhp more than it did in the earlier i8 Coupé at 141bhp. This is delivered along with the same 184lb ft as before, through a two-speed gearbox to the front wheels.

Combined with the unchanged 228bhp delivered by the turbocharged 1.5-litre three-cylinder petrol engine mounted transversely up back in a mid-rear position, this provides the roadster with an overall 374bhp and a theoretical maximum torque loading of 420lb ft, although the latter is continually regulated depending on grip and traction levels, with drive delivered to the rear wheels via a six-speed torque converter-equipped automatic gearbox.

BMW i8 Roadster 2018 review © Autocar BMW i8 Roadster 2018 review

Further modifications have also been made to the lithium-ion battery, which is mounted wholly within the centre tunnel. While similarly dimensioned to the unit used previously, its cell capacity has been raised from 20Ah to 34Ah. The use of fourth-generation cells have also increased its energy capacity from an earlier 7.1kWh to 11.6kWh.

As a result, BMW quotes a pure-electric range for the i8 Roadster of 33 miles - some 10 miles more than it quoted for the earlier i8 Coupé. 

As well as recuperating energy under braking, the roadster uses the same electric motor at the rear as the i8 Coupé. It acts as a generator to top up the battery on the overrun. Around town in eDrive Eco mode, progress is whisper quiet and quite urgent as the upgraded electric motor provides drive exclusively to the front wheels.

BMW i8 Roadster 2018 review © Autocar BMW i8 Roadster 2018 review

But with a turning circle of 12.3 metres overall, manoeuvrability in tight urban conditions certainly isn’t one of this car’s biggest strengths.

But don’t let anyone tell you the i8 Roadster is lacking speed. There are quicker cars at this price point, granted. But the combination of electric and petrol power in Hybrid Drive Sport mode provides the car with both brutish four-wheel drive accelerative qualities off the line and great long distance touring traits on the open road. There is excellent flexibility across a broad range and, once you’ve wound on sufficient revs, there's a stirring engine note, too. 

Despite changes to the suspension bushings and a new vertical strut for improved wheel control at the rear, there remains some annoying tyre roar on less-than-smooth surfaces. However, the secondary vibrations through the carbonfibre body structure, both from the road and engine, are now much better damped than with the earlier i8 Coupé in a move that helps improve overall refinement. 

BMW i8 Roadster 2018 review © Autocar BMW i8 Roadster 2018 review

Further improvements have been focused at the steering. It receives new mapping, which brings greater sensitivity around the straight ahead. It’s still quite light by sports car standards, but there’s now added weight off-centre. Overall, it endows the i8 Roadster with a more responsive feel than the i8 Coupé, allowing you to place the car more confidently in corners and indulge in its excellent dynamic capabilities.

Should I buy one?

There’s a multi-faceted appeal to the i8 Roadster that you don’t find in any obvious open-top rival.

BMW i8 Roadster 2018 review © Autocar BMW i8 Roadster 2018 review

You can cover large distances with effortless progress and great fuel economy, switching in and out of eDrive Eco mode into Hybrid Drive Sport as the conditions allow. The driving position is excellent, with fittingly sporting qualities within an interior that is appropriately high on quality.

It may have been a long wait, but the i8 Roadster does not disappoint. The changes BMW has brought to both its powertrain and chassis not only endow the car with sharper performance but also more endearing driving qualities than the earlier coupé.

With the adoption of these changes, the fixed-roof version of the headlining i model also promises to take a step up the sports car pecking order.

a car parked on the side of a mountain © Provided by Haymarket Media Group BMW i8 Roadster specification

Where Mallorca, Spain Price 124,735; On sale June; Engine 1499cc 3-cyl turbo petrol, 129bhp electric motor; Power 369bhp at 5800rpm; Torque 320lb ft at 3700rpm; Gearbox 6-spd automatic; Kerb weight 1595kg; Top speed 155mph; 0-62mph 4.6sec; Fuel economy 134mpg; CO2 46g/km; Rivals Jaguar F-Type convertible, Honda NSX, Porsche 911 Targa

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