Lordy that looks a bit futuristic. What is it?The i8 is BMW's new-age sports car. So new-age, in fact, that its engineers refuse to say how it does against that age-old sports car measuring stick, the Nürburgring lap time. Guess that makes it, right out of the box, James May's favourite sports car.Instead, they maintain it's a 'sports car for the real-world'. And they just let TopGear out to have an early drive. Well it's certainly welcome into my world.As a part of BMW's new i brand, it shares a lot with the i3. But it's also strikingly different. It uses a carbonfibre passenger cell like the i3. It has a plug-in battery like the i3. But it's not pure electric drive. Instead, most of the propulsion is taken care of by the piston engine, linked via a six-speed transmission to the rear wheels.It's also very, very low, very grippy and massive fun. Both in a straight line and in corners. Oh and it looks like it's just been beamed down from Planet Astonishing.But it's making my eyes hurt. Can we stop now?Sorry about the swirly disguise in these shots. The 'clean' unveiling will be at the Frankfurt Show on 10 September. I was in a prototype, though the engineers say it feels almost exactly the same as the car that will go on sale in April internationally.Suppose I should know about the plug-in hybrid bit I guess. But will you make it snappy?Because it has a pure electric mode from its mains-chargeable battery, you're expecting it to be silent and smooth and nippy in town. And because it also has a hybrid mode, you're expecting it to be efficient in give-and-take suburban driving. Yes and yes. It is both those things.Fine fine, now what's it like as a sports car?Well all you need to do is nudge the transmission lever out of the PRND side of its gate and into the S side. This activates sports powertrain mode, sports steering mode and sports damping mode. It allows the engine and electric motor to pull flat-out, so there's 360bhp in a car of just 1490kg. It's good for 0-100 in less than 4.5 seconds. Let's explore.Remember, everything about this car is as small and as light as possible while still getting the job done. Even the mid-mounted petrol engine. It's a 1.5-litre three-cylinder turbo. Basically it's the one off the next Mini Cooper, but for i8 duty it's boosted up to 230bhp. Sounds like a recipe for peakiness and lag? Well not here, partly because it has all the latest anti-lag tech. But also because attached to it is a small electric motor-generator which does a remarkable job of filling in the low-rev lag, even if it doesn't add to the engine's power when boost has been built.The rest of the urge comes from the electric motor that drives the front wheels. That's worth another 130bhp. All that said, it didn't feel like quite a 4.5-second car to me. Maybe because its off-the-line sprints get a helping hand from the effective 4WD of the electric front motor, so the figure is flattered. Whatever, it's quick enough to be called a sports car.But more important is how controllable it is. However good a chassis is, if you can't meter out the power flowing through it you'll never get into the driving groove. The i8 does the job better than I'd dared hope.But doesn't such a complicated drive system feel a bit weird?Because the petrol engine drives through a sharp-witted six-speed auto 'box with paddle over-ride, it all feels remarkably natural and answers the accelerator promptly and progressively. The front electric motor is calibrated to match its efforts. You don't feel the car's two ends are disagreeing.It sounds good too. In sport mode they have taken the exhaust and electronically boosted the nicest of the three-cylinder harmonics. The result is a bass-heavy thrum in mid revs, that hardens nicely as you get to the red at 6500rpm. No it's not as epic as the departed V8 M3 at full scream, or even a 911, but it's certainly no deal-breaker.And the handling?All the sports car basics are in place for good cornering, The overall weight is trim, the centre of gravity very low, the track wide, the masses concentrated inside the wheelbase.And it works. There's a wonderful eagerness to the steering, and the feeling that the anti-roll bars really don't have much to do. Through S-bends the tidy flick of the body is a delight. Fast corners are neutral and confident.Something odd, though\: in slow ones, especially on the test's sections of greasy damp newly-laid tarmac, you're fed a big helping of pre-apex understeer. The engineers say this is the tyres, and that they're confident it'll be fixed in the nine months they have in hand until production.Otherwise, more excellence to report. The steering assistance might be full-electric, but it sends up lots of feel, unweighting when the nose hits a crest or a damp patch, lightening too when you power on and edge out the tail, nibbling away as you sweep through a fast corner. Grip is strong, even if the tyres look skinny. That's because the centre of gravity is low, so the job is shared more equally between the inside and outside tyres.By varying the torque to the front motor through bends (less early in the bend, more through the apex and on exit) the i8 gets the most out of the tyres and gives the most confidence to the driver. But it also allows a bit of adjustability through the right pedal. I don't suppose it's a big smoky track drifter, but remember, it's a real-world sports car. Not a hardcore weapon, not a supercar.How long will it keep it up?Good question. On most tracks, the power would deplete after a few laps. That's because the strategy in sport mode is to use the rear generator and indeed the front motor to fill up the battery whenever the engine's entire efforts aren't needed to drive the car. But on a track where you're either at full throttle or full braking, it wouldn't get enough light-throttle periods to do its recharging thing.Hence the silence on a 'Ring time. But really, on any road, even an autobahn going at a sustained 250kph, the engine gets enough time to charge the battery. And then when you ask for the full beans you can have piston power and electron power together.Is it bumpy?Because you're sitting low, your head isn't levered about by lateral bumps, so the ride feels placid. Sure there's a sharpness to the damping in sport mode, but the springs aren't that hard, and comfort mode is exactly that.How do those other modes work?Comfort mode is the default. The car operates as a hybrid. Imagine you've started off with a mains-charged battery. It only takes 5kWh, which equates to two hours off a mains socket. Now the car will use front-wheel electric drive in most conditions up to about 70kph, because that's efficient. Then it'll use the engine above that, because engines are good for higher speed. Unlike in sport mode, it won't use the engine to recharge the battery (at least not until it sustains the battery at about 35 percent).And it won't use the electric motor to add to the engine's power. So overall performance is lower. But it's still a nice progressive powertrain in this mode. It isn't making too many distracting transitions between electric and petrol power. Also, the engine's sound enhancer is switched off, so you notice it less.Economy?Used this way, the official figure is going to be 48kpl and 59g/km CO2. Of course like any plug-in hybrid number, it doesn't reflect the energy from the electricity you've bought. Even so, it might well reflect the amount of petrol you put in, if you're commuting. And the tax advantages will make it cheaper to own than a Carrera 4S PDK.A fairer comparison might be this. The engineers claim that even if you never plugged it in, real-world you'd use little over half the fuel you would in an M3.Then there's zero-petrol, zero-tailpipe-carbon, full-electric mode. Here the engine is stilled, and the front motor gets a unique trick\: it's dropped into a lower gear. That way it can accelerate off the line pretty smartly - up to the tyres' wheel-spin limit. And it'll stay that way to 120kph.So now you're wafting silently through a town, enjoying the remarkable dual character of the car. And maybe looking around at the rest of the cabin.Ah yes, the i3 has lovely furniture. Is the i8 as good?Everything about the interior is designed to be spare and light. The seats are thin but do the job; the dash screens look weightless. The huge door lifts out and up with one-hand ease, yet it shuts reassuringly solidly.How come they made it so light?The tub is carbonfibre, made in BMW's new low-cost method. To either end are bolted aluminium sub-frames for crush zones and to carry the powertrains and suspensions. Most body panels are plastic, but the doors and front bonnet are aluminium, and the roof is carbon in pursuit of a low C of G.The side glass is amazing. It's the same stuff as smartphone screens, very thin and light, but strong and actually flexible. There's clever stuff like that all over the i8.What about the fancy aero?It has a Cd of just 0.26. The concept-car shots here show the way the air is shepherded in layers between some of the body panels. It goes through the front bumper and past the wheels in a curtain. It's taken in below the number-plate, through the radiators and out of an opening the front bonnet. It's pulled into the engine bay from below. It's taken in ahead of the rear wheels and channeled through the rear diffuser. It wraps around from the sides to the rear screen, for a highly tapered low-drag boat tail.Is it going to stop the traffic?Probably more than a Porsche 918. Nothing else looks remotely like it. And that's before we even get to the doors. OK they don't have glazed lower panels like the concept, but can you think of another 2+2 that has scissor doors?Does it really make sense though?Like the i3, what BMW has done with the i8 is re-invent the whole car in search of efficiency. Everything works because of everything else. None of its elements - carbon shell, hybrid system, radically down-sized engine, the packaging, the aerodynamics - makes sense alone. They all work because the others reinforce them.As project chief Carsten Breitfeld says, it's important to remember it's an i8 not an M8. Not a track-day hero, but a sports car for all the other days. It's meant to show that sports cars can survive and adapt. And do it even if a world of incentives for low-carbon cars and deterrents for the opposite sort.He doesn't say, so we will, it's also a captivating piece of design.