Driven: BMW M550d xDrive

Enough discussion of Bavarian breakfast sausages, time for Harris to get to the, er, meat of the BMW M550d

Last week's live blogging exercise was a bit of fun, albeit lacking any real detail about the car and expensive. The iPhone data cost £120. Everyone say a big thank you to Stuart for that.

Three turbos and a whole lotta complexity

Now I have just been sitting reading the technical document handed out by BMW last week explaining the key features of this new 381hp/546lb ft motor. See below to enjoy it in its full, unexpurgated glory.

Beyond the minutiae of intake, exhaust, block and head connection techniques and the clever inter-play of those three turbochargers, I was left with one overriding thought. Boy do you have to engage in some pretty crazy tomfoolery to make diesel oil do exciting things.

There is just so much going on, so much cajoling of that nasty, greasy, smelly fraction of crude oil, it does beg the question: is it really worth the hassle? I mean, would a 550i actually do a better job? All the V8 petrols are now smaller capacity twin-turbos, so the 'effortless' argument is no longer an easy diesel victory.

Big roads and Autobahns are natural habitat

Three times the fun
What never ceases to amaze me is how current motor car engineers execute these staggering solutions to the performance/economy predicament, and then leave the driver completely unaware of the alchemy under the bonnet. I started the M550d xDrive and tootled off down the road like it was a 520d. The only clue you are driving something very special is in the rather clumsy, hi-fi augmented intake noise (in Sport Plus mode) that sometimes sounds like a Corrado VR6 that's dropped a cylinder. Minutes later you are doing an indicated 159mph and wondering what idiot felt it necessary to fit a speed limiter. Oh, and during that bout of acceleration you wondered if at times the M550d didn't sound really quite good.

There is actually a very simple reason for this car's existence: Audi. The rear-wheel-drive mantra has served BMW well for decades, but the popularity of interstellar 4WD machines from Ingolstadt forced a change of attack from Munich. It needed something to appeal to affluent folk who like driving to ski resorts in winter time. This is that riposte. But the car won't be coming to the UK, nor will it end up in the States.

Dials go red at night, like a real M car!

Comfort zone
On the Autobahn, or wide, sweeping national highways, this is the type of car you'd select to persuade curmudgeons unwilling to accept the progress of modern cars. It hauls from idle and then persists until a most un-diesel 5,400rpm. The real advantage it offers over the 535d is in the upper rev range (can you call 4,000rpm 'upper'?) where you feel that extra, smaller compressor urging on this near-two-tonne machine.

Why a car with such immense core strength should need eight forward gears is anyone's guess. By diesel standards the M550d has a gargantuan power band, but that's still much smaller than a gasoline engine's and juggling all that torque with eight ratios offers the potential for a shambles.

Bigger bootlid required to fit badge

The ZF unit works well here, but its eagerness to kick down does rather spoil the party. I love feeling when these torque-monsters heave from 1,500rpm and hang on to a gear, but with the transmission in Sport it just wants to shuffle down the 'box. I found myself putting the thing into Comfort just to avoid the downshifts. They're smooth and snappy, but they interrupt the surge.

The diesel M5?
Is it as fast as an M5? Nothing like. Its 4.7sec 0-62mph time is a corollary of stacked gearing and 4WD traction. Above 100mph the new M5 would have to use all of its firepower - but that's always the case for the valiant petrol machine versus the fast diesel, no? Even so, it would then teach the M550d a lesson or two. And that's before we even discuss the subjectives, throttle response being the big one. What happens when the taps open is very impressive. The sensation of doing so is one of complete detachment. Personally, in this kind of car that doesn't worry me one bit, but some will find it irksome.

'A nice place to be' and all that

My test of fuel consumption was woeful, and I apologise for that. We had to drive around Munich like dervishes trying to shoot a video, and spent most of the time at full throttle. This gave 20.1mpg over 160 miles. Now at face value that looks terrible, but when I did the same in an M5 last year, it was into single figures. I don't subscribe to talk of 40-plus mpg unless you drive it in a manner that proves you should have bought a 520d instead, but mid-30s looks very possible. That's 10mpg more than an M5 in like-for-like driving.

Piste basher
I have never before driven a 4WD BMW at over 150mph, but can report that they are more stable than their 2WD relatives. No great surprises there. Few cars feel more comfortable at 155mph on winter tyres than this one. Am I allowed to say that?

Built for rich Germans to visit ski resorts

The benefit 4WD brings on normal roads is less clear. Revised springs and dampers and bigger anti-roll bars give more support and make the car firmer than a 5 Series M Sport, but they don't remove the feeling of mass. I thought the M5 felt big and heavy, the M550d to me was lazier in direction changes and less nimble. Again, it was on winter tyres so I can't draw a definitive conclusion, but I think it's fair to say that the M550d is better suited to bigger roads and longer journeys. What it does have is far better traction than an M5. Surprise, surprise. In reality, any car looking to usurp Audi as the Verbier chariot of choice needs to be 4WD, so it fits the package.

So what we have here is a great all-rounder. It's not an emotional statement like the M5 and the more time I spent with it, the more I appreciated the subtlety. Remove that rather clumsy boot-badge and it could be any-old five. Specify the Touring body and you surely have one of the most complete cars on sale. A diesel with massive performance potential; a ski-taxi to shame Audi. Yes, it was worth it.

BMW M550d xDrive
Engine: 2,993cc 6-cyl diesel, tri-turbo
Transmission: 8-speed auto, four-wheel drive
Power (hp): 381@4,000rpm
Torque (lb ft): 546@2,000rpm
0-62mph: 4.7 sec
Top speed: 155mph (limited)
Weight: 1,970kg (EU)
MPG: 44.8mpg (NEDC combined)
CO2: 165g/km
Price: N/A