Has the adoption of four-wheel drive for the first time on a BMW M5 compromised the super-saloon's famed handling purity? Of all the hardware on the new BMW M5 – and there is a lot of hardware on the new BMW M5 – there is one piece of kit of which BMW engineers are particularly proud.It's a little black box that sits beneath the bonnet, and Dirk Hacker, BMW M division's vice president of engineering, says that it is "the real breakthrough". What they call the Central Intelligence Unit integrates the controls of all the new M5's hardware subsystems in one place.I think it's a bit like the one in the latest Ferrari 812 Superfast: it considers all of the inputs you're making, and all the feedback the car is giving it, to, Hacker says, "control every subsystem governing lateral and longitudinal dynamics". An automotive one ring to rule them all.And in the M5, there is a lot of hardware to rule. The big headline is 592bhp and a four-wheel-drive system to deliver it, for the first time in an M5.Perhaps for the first time in a proper M car if you're disinclined to count X models, as I'm happy to. It's a variable 4WD system, with three modes of its own, and an active M differential at the rear, as on rear-wheel-drive M cars. But there are more hardware and software systems than just these, too.Externally this new M5 packages all of this kit together fairly subtly. Big arches and muscularity seem to be reserved for M's 2,3 or 4, but I don't think they've ever been present on an M5. Then it is an executive express, after all, and quite keen not to lose the 'executive' part.Look closer, though, and the hints of the underlying performance are there. There are acres of cooling vents at the front. There's a diffuser flanked by quad exhausts at the rear.There are 19in or – as likely, and as tested – optional 20in wheels. And, in between all of those, there are some lightweight panels, aluminium in some places, and with a carbonfibre roof – useful not just because it reduces mass but because of where it reduces it: high, thus lowering the centre of mass. The M5 is a 1930kg car, only about 15kg lighter than the last one – but hey, weight loss is weight loss.The gearbox is now an eight-speed torque converter automatic rather than a dual-clutch 'DCT' auto, which usually has the advantage of being slightly lighter. I think it matters here too because, for all the improvements in DCTs, a conventional auto is still more refined at low speed. Besides, pretty much as soon as you're rolling, they lock up these days so don't really slush any energy any more.Upshifts are quick enough for me on autos – DCTs have the next gear-up engaged so kickdown takes a while on those anyway and, under braking, blipping the throttle means that to an extent it doesn't matter how fast downshifts are.So, as with, say, an Aston Martin, I think a full auto would probably suit an M5 anyway.The gearbox hangs from the back of a 4.4-litre V8 engine, as in the previous-generation M5, but there's quite a lot about it that's new here. It has new turbochargers and a higher injection pressure (350 bar, incidentally), new cross-bank exhausts and a smaller, more efficient cooling system.The upshot, in addition to the 592bhp at 5600-6700rpm, is 553lb ft at 1800-5600rpm, because that's how big super-saloon numbers are these days. Thirty horsepower shy of a McLaren F1. What a world, eh?
