Going the distance: BMW i3 Range Extender driven

13 May 2014

BMW i3 Rex front view

BMW i3 Rex
Rating: 5 out of 5 stars
Good: quick, quiet, unlimited range
Bad: fiddly Rex controls, small boot
Price: from £28,830 after grant
The battery powered BMW i3 provides a range of 80 to 100 miles between recharges. In practice, this means that a round-trip to any destination more than about 35 miles away must involve some sort of forethought about where to stop and plug the car in. While that threshold will be just fine most of the time – about 90% of UK car journeys total less than 20 miles – the other 10% could occasionally prove to be a pain. It’s not easy being green, as the saying goes, and that counts for green cars too.

Browse the BMW i range online and you’ll learn that the company aims to address the issue with service bundles that unlock public charge points and provide easy access to conventional BMWs for longer journeys. Subscriptions start at £40 per month.

Or, alternatively, you could bring your own charging facilities with you.

The BMW i3 with Range Extender – or i3 Rex to its friends – costs an extra £3,150 over the base i3, bringing the starting price to £28,830, after the contribution of the Plug-in Car Grant. In return the car gains a nine-litre petrol tank safely swaddled in the nose, plus a 650cc two-cylinder engine stashed under the boot floor. Slightly wider rear wheels are also fitted, providing more grip to compensate for the 125kg or so added at the back.

BMW i3 Rex side view

The engine never drives the wheels, instead firing up to run a generator, supplying fresh electricity for the car’s electric motor on demand. Each fill-up will keep the i3 Rex going for a good 60 miles or so before refuelling, and it can carry on in this mode indefinitely.

The silver i3 Rex I’ve borrowed has helpfully been supplied pre-depleted. As I climb aboard, the battery gauge has already fallen below a quarter full, predicting an electric range of only 12 more miles. The tank is full, however, showing another 60 miles on top. That’s plenty to cover today’s varied route.

All i3s are equipped with a 125kW (170hp) electric motor, whereas the range extender engine is rated at 25kw (34hp). It doesn’t take much arithmetic to realise that the engine can’t generate enough juice to underwrite full performance all on its own. To make up the difference, the i3 Rex will need to call on its battery from time to time even when the generator is running. For this reason, it’s a good idea to wake up the engine before the battery runs down completely. That will give a bigger on-board buffer for the i3 to play with – drawing on battery power for brisk acceleration and putting energy back in during braking, or when the motor doesn’t need all that the generator provides.

BMW i3 Rex interior

So our journey begins by telling the car we’re going to need the generator before we’re done. Using the iDrive controller between the front seats I scroll through options on the central screen, to tick the box marked “Hold state of charge”.

Actually, I don’t have to scroll through the options. Running across the top of the centre console are eight buttons, each of which can be set up as a shortcut through the maze of digital screens. A button might call up a favourite radio station, or it might whisk you straight to a vehicle setting. They’re touch-sensitive too, so running a finger along all eight buttons provides a quick on-screen reminder of what each one currently does. In this particular i3, button 7 has been set up to go straight to the Rex options screen. The shortcut saves time, but even so, I can’t help feeling that a dedicated “Hold” button might have been a better idea.

BMW i3 Rex rear view

Moving off, the rear-mounted engine doesn’t immediately fire up and even when it does hum into life a few moments later, it’s surprisingly subdued. It thrums away quietly, running at constant rpm, reminiscent of a washing machine on spin cycle in another room. Push on above dawdling pace and you seem to leave even that muted noise behind, smothered by the modest rise of wind and tyre roar. At a standstill, the engine quickly shuts down again to preserve the peace.

The battery powered i3 is one of the quietest cars I’ve ever driven, and I’m happy to discover that the i3 Rex remains among the most refined.

As with the battery i3, the Rex edition feels effortlessly, uncannily brisk. Getting to 62mph takes 7.9 seconds (0.7 seconds slower than the pure battery car) but it’s the manner of getting there that strikes the most. With no gears to swap and no pause for revs, the i3 seems to change speed in an instant. Whether pulling out of a blind junction, joining a busy roundabout or overtaking on a short country straight, the i3 inspires sports-car levels of confidence.

BMW i3 Rex on the move

Lifting off the throttle triggers quite a stiff level of regenerative braking, feeding energy back into the battery as you slow and feeling a lot like you’ve accidentally left the handbrake on. It takes some adjustment and is the only aspect of driving an i3 that I don’t much like. The knowledge that it extends electric range does help to ease my gripes, however. A predictable level of automated recuperation is more efficient than relying on the random stabbing of my foot on the brake, BMW engineers have helpfully told me in the past.

Grip and handling are more pleasantly predictable, as you might expect from a BMW. The tyres may be skinny but the wheels are 20 inches across (up from the standard 19s), giving an elongated contact patch for clinging onto today’s sodden tarmac. The body stays impressively upright through corners, aided by a low centre of gravity. The hefty mass of lithium ion batteries is carried flat between the axles, in an aluminium frame, while the upper body uses simple plastic panels over lightweight carbon-fibre. Indeed, you can see the bare carbon structure ringing the aperture whenever you open a door.

BMW i3 Rex carbon fibre

On the move, the steering feels light but extremely precise, freed from corruption by the rear-wheel-drive layout. The thin-rimmed, two-spoke wheel is a lot more lovely to hold than to behold, given that it looks as if it’s been bolted on upside down. And the remainder of the interior is an equally surprising mix. A recycled material that looks like grey fabric but feels like hard plastic has been extensively applied, and won’t be to everyone’s taste.

You also sit quite high atop the layer of batteries, which can feel a little odd to begin with. But the interior immediately feels welcoming, spacious and airy – even with the standard black-and-blue cloth upholstery – helped in today’s car by glass panels above the front seats.

BMW i3 Rex steering wheel

Rear-hinged back doors offer easy access to the second row of seating, though I keep forgetting that the rear door won’t open unless the front one is open too. The boot is high-set and small at 260 litres, and is not affected by choosing the Rex edition. At least it’s easy to flop the 50:50-split rear bench forward from behind the car.

At the end of my test I’m pleasantly surprised. On batteries alone the i3 is a joy to drive, and the Rex edition does nothing to dampen that verdict. It does have its foibles – most notably the fiddly process of holding the battery state – but the addition of a standby engine has transformed BMW’s innovative electric baby. It has extended its range not simply in terms of miles, but from niche urban runabout to true go-anywhere all-rounder.

BMW i3 Rex from the front

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