BMW X5 – reviewing the 2007 launch April 3, 2009
Posted by richard in : Uncategorized , trackbackWhen you sell 41 percent of all models in just one country, you listen to what they want. So, when the US demanded BMW improve the ride quality of its X5, the company did just this.
That’s what BMW’s Albert Biermann told me as the X5 was launched. I’ve just dug out my notepad from the launch event back in 2007, and am still startled at the number of ‘interesting point’ asterisks dotted through it.
I was amused, for example, to hear him describe the driving position as ‘command position seat’. Hasn’t Land Rover got the copyright on that? He also pointed out the four interior colour ‘worlds’, the six trim colours and five trim types. Plenty of choice there, then.
It was the engineering that I was waiting for, though. I didn’t have long to wait, before Biermann dived in. The current X5, for example, is 15 percent torsionally stiffer than the old one was. 27,000 Nm/deg is the slightly esoteric but quoted figure. We need context.
We were given it.
Group A E30 M3 race car? Made from high-strength steel, at huge expense? Torsional stiffness, 22,000 Nm/deg…
The aero drag factor of the X5 is 0.3, thanks to ingenuity in the rear lights, the roof spoiler and the underbody. It’s better, despite bigger wheels, and has reduced lift, too. The ride’s also smoother, courtesy of fourth-generation runflats. And FlexRay means damping forces are constantly varying every fraction of a second.
You could sense his disbelief at how rivals have fuel consumption some 27 percent higher than the X5. ‘Despite being less powerful and torquey!’ One aid here is reducing slip in the new auto, gaining 3 percent mpg, plus 50 percent faster gearshifts. ‘The torque converter locks up almost all the time.’
Double wishbone front suspension, though – why? Well, it means the strut only encounters damping forces. With the old X5, its fabled dynamics demanded stiff dampers. Using MacPherson strut, this introduced compromises in a heavy SUV:
1 – Pistons experience big side forces, which results in stiction and leads to a pattery initial ride. Double wishbone doesn’t suffer this.
2 – For rigidity, MacPherson strut yields a thicker piston rod diameter, which restricts you in bump and rebound. With double wishbone, this is smaller, giving you more bump and rebound ‘play area’. This improving ride once again.
(Oh, and it’s not coming en masse to BMW saloons, he later said. They’re light enough for all this not to be an issue. Unless, of course, they have a ‘7’ badge on the back.)
At the rear, there’s an axle air spring. This decouples the load from the spring rate of the car, and means the same ride height can be maintained. It helps dynamics, as axle kinematics of the rear won’t change. It means you have the full travel of spring for all loads – the ride frequency can be constant for all loads.
The X5 also introduced BMW’s Integral Chassis Management concept. There’s so much theory here, it’s a separate post on its own. More on this later…
But, back to the start. So, the US made the X5 the car it is, then?
No assures Biermann. ‘BMW has world cars.’ While it has to fit in the US, he says, the company’s philosophy means it won’t be compromised for anywhere else. ‘The US can’t influence an overall concept, just as nowhere else can, either,’ he said.
It was the last question of the press conference, he thought. That’s us placated, he reckoned. But, no. Just time for one more. ‘When are you putting the V10 M5 engine in?’ enquired a colleague, boldly. Biermann feigned surprise. ‘You don’t have enough power already..?’
Today, of course, it’s confirmed his tongue was in his cheek at the time.
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