BMW doesn’t do things by halves. This is their first full hybrid model, the ActiveHybrid X6, and it’s the most powerful hybrid in the world. It combines a 407bhp 4.4-litre twin-turbocharged V8 engine with a fiendishly complicated gearbox that contains two electric motors, one optimised for low-speed running, one to boost power at higher speeds.
The X6 ActiveHybrid’s electric motors can produce 91bhp and 86bhp, respectively, but the total combined output is pegged at 485bhp and 575lb ft – lessening the load on the V8 petrol engine and further reducing emissions.
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So the BMW X6 ActiveHybrid is a Prius in big, bad SUV wolf disguise?
Hardly, but the X6 plays all the usual hybrid tricks. The motors act as generators under braking (electricity is stored in a nickel metal hydride battery with a capacity of 2.4kWh located underneath the boot floor), which is then used to power the motors when driving under electric power alone or when supplementing the V8.
BMW claims the ActiveHybrid X6 will accelerate from 0-62mph in 5.6-seconds and hit 155mph, despite weighing a frankly absurd 2525kg – 260kg more than the conventional xDrive50i fitted with the very same V8 engine.
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Woooah. So this is one lumbering, big fat beast?
Oh yes. But the tech does its damnedest to offset the weight to some extent. The incredibly complicated gearbox is at the heart of the Active Hybrid: It has elements of a continuously variable transmission with seven ‘virtual’ gears, but at higher speeds runs through more conventional planetary gearsets with multi-plate clutches, all the time supplemented by the two electric motors.
Developed by GM, Mercedes and BMW in partnership it occupied 150 engineers for a full three years. I can’t begin to do justice to its inner workings (indeed, BMW admitted that the press material deliberately doesn’t try to explain how the ‘box works because it simply can’t be put into layman’s terms) so perhaps I should just describe how it feels from behind the steering wheel…
Tricky that, as such is the refinement of BMW’s application of the hybrid system that it feels freakishly like the xDrive50i. Sure, there are some striking differences – for example when you press the ‘Start’ button the V8 doesn’t fire-up at all, rather a little blue needle underneath the main rev counter flicks from ‘Off’ to ‘Ready’.
Select D in the same way that you would with any other X6, brush the accelerator and the big SUV glides silently away on pure electric power. On light throttle openings the X6 can propel itself to 37mph without the help of the V8, after which it kicks into life with the merest hint of shunt. The range of electric drive is just 1.6-miles, however.
A 1.6-mile electric range! They won’t be giving Toyota any sleepless nights…
That sounds pretty hopeless but in practice the X6 does seem to run on pure electric power quite often, and around town the engine shuts off if you’re coasting at less than 40mph – the battery simultaneously powering functions like the air-conditioning and power steering and also being fed by the electric motors as they generate electrical energy on the overrun.
A graphic on the iDrive display informs you whether you’re running on electric power, petrol or a combination of the two – useful as the V8 is incredibly quiet at urban speeds. The motors also provide up to 0.3g of braking energy before the conventional braking system has to get involved and detecting the switch from pure electrical resistance to a caliper gripping a disc is very tricky. It’s not quite seamlesss, but it’s close enough so as not to matter.
And what of the performance benefits?
Well, this is a very heavy car, but it feels absurdly muscular at any revs and sounds terrific when you do decide to call upon all the twin-turbo V8 and electric motors can give. The ActiveHybrid X6 has a full 75lb ft more than the X6 M and although it isn’t quite as ferocious as the M Division’s vision of the ultimate SUV it’s still a mighty fast bit of kit.
There must be a big but coming… surely this isn’t actually that efficient, is it?
Well, sort of… BMW claims that the ActiveHybrid is 20% more efficient than the pure petrol model, with a combined 28.5mpg and 231g/km of CO2. Matching those claims isn’t easy and nobody on the launch averaged much more than 20mpg. My personal record after a day’s driving mainly within the confines of downtown Miami was 16.9mpg.
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And so I found myself wondering what the Active Hybrid X6 was all about. The way it generates and distributes electrical power is ingenious and perfectly integrated into the conventional driving experience. In that sense it’s a triumph.
But, sheepishly, the drivetrain engineers admit that this complicated and expensive system is simply a means of prolonging the life of V8s a little longer, easing the conscience of those who still want big grunt in even bigger SUVs; that in Europe diesel will remain king for some time to come and that this is really a product for the V8 and hybrid obsessed US market.
The new BMW X6 ActiveHybrid won’t be offered in right-hand drive and in Germany it costs €26,000 more than the xDrive50i. It demonstrates with devastating efficiency that fitting chuffing great V8s into stuffing great 4x4s isn’t viable any more.