Why Renaultsports don’t have rear spoilers April 18, 2009
Posted by richard in : Minutiae of cars , 3commentsRENAULTSPORT Megane customers want sporty cars, but they also want low running costs. Apparently.
That’s why Renault doesn’t fit a rear spoiler.
See, it would up the drag, worsen the Cd, and push up mpg.
That’s also why, it was explained to me on the car’s launch, there’s a RenaultSport Megane diesel – with multi-stage Piezo injectors, the last pulse of which is charged with burning off soot emissions. Overall, 45mpg. Good, oui?
Fear not though, I was told. Being racy is still the prime reason for the RenaultSport.
The need for bigger brakes, for example, led Renault to develop trick double-axis front suspension. Another benefit of which just happens to be high stiffness levels.
As an engineer explained, it means there’s ‘no wobble under hard acceleration, so no geometry loss, so no steering squirm.
‘During cornering, forces on the front outside corner are high, which distorts the suspension. Not on double-axis though, which is twice as stiff as MacPherson strut.’
And that’s not all. ‘Less parasitic movement means less need for steering correction, so it’s more precise…’
Blimey. But yet more precise still is the Cup version. This has ‘reinforced dampers, 37 percent more rear spring stiffness, and ESP that can be turned completely off.’ Hardcore features for hardcore drivers.
Clio Cup Runneth Over
He was a handling geek, my insider. And how I delighted in speaking with him, over the fizzy water. I soon got him onto the Clio RenaultSport, where his revelations were just as cool.
Did you know, for example, the Clio’s seats help lower the car’s centre of gravity? It’s also 27 percent stiffer in spring, and 10 percent firmer in damping… ‘And the double-axis front suspension separates steering efforts from the damper.’
Now, it was a veritable flurry of gems from him. Four-pot Brembos come on the Clio, which he revealed to me (but not the guys within Renault who control costs) are ‘oversized’.
The rear diffuser? It has a 26 degree angle, creating a depression under the car, which ‘weights’ the back down at speed. Not only does it reduce lift by a factor of 3, but it also ‘primes’ the suspension for best response at speed.
Genius. And for real.
I can’t repeat what he said about makers who fit false rear diffusers.
‘The diffuser also does away with the need for a rear boot spoiler,’ he added.
Which takes us back to the start. That’s why Renault doesn’t fit one to the Clio RenaultSport, either. But why, ahem, Vauxhall has to fit one to the ‘diffuser-equipped’ Corsa VXR. Ahem, ahem.
How Chevrolet today became cool
BMW X5 – reviewing the 2007 launch
BMW X5 – reviewing the 2007 launch April 3, 2009
Posted by richard in : Uncategorized , 4commentsWhen 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.
NEW: Bentley Continental GTC Speed photo stream on Flickr March 25, 2009
Posted by richard in : Uncategorized , 2commentsWant to see what I’ve been up to on my latest launch event? Well, check out my Bentley Continental GTC Speed photo stream on Flickr.
And be sure to come back here over the next few days. As ever, I’ll be charging through all my notes and feeding back to you.
Check out the images for a feel of what was what in Crewe!
Pre-launch impressions: Bentley Continental GTC Speed March 24, 2009
Posted by richard in : Uncategorized , add a commentWhat do I expect from the Bentley Continental GTC Speed? Something very, very fast, that’s what.
Last year, I drove both the standard Continental GT Coupe, and the livened-up Speed variant. Both worked together, to turn me from a Conti skeptic into a convert.
First thing I did when I got back home was check out Auto Trader, to see how much early-gen ones went for. (£40k and no I can’t, to pre-empt any questions).
The Speed line, which brings more power, sportier handling and subtly enhanced looks, has already instantly won the majority of GT Coupe sales, and is doing similarly good business for the Flying Spur saloon. Now, it’s the turn of the GTC Convertible.
Coupled with a mild facelift for the 2010 model year, Bentley’s given us the full fat 600bhp Speed drop-top 2+2, creating its fastest-ever convertible in the process. 200mph do ya?
The overriding impression I took from the GT Coupe was one of completeness. This really was a car that tuned into my psyche – it wasn’t particularly overtly sporting, or dramatic, or intense. It was just ‘nice’. Accurate, agile way (way way way) beyond its size and weight, and generally pretty lush.
I blow hot and cold with convertibles. Currently, I’m on a downer with them – preferred the BMW Z4 when it was imitating a Coupe rather than being a Roadster. How will I get on with the Bentley, then? Well, by now, I’ll already know. And will be letting you know in due course…
BMW Z4 chassis secrets March 22, 2009
Posted by richard in : Uncategorized , 4commentsHeinz Krusche is BMW’s chassis guru. I’ve met him several times, and always enjoyed top insight from him (not least his tales of how he keeps DSC turned on for the road – but ‘always’ turns it off when on track…).
Such people exist in every car company, but they don’t always have the power of Krusche.
He wields the same sort of influence as Jost Capito at Ford. There’s another genial genius – and look at how well Fords drive. Lotus, too, has Matt Becker, ensuring that every single model drives sublimely.
So, speaking to Krusche is always enthusing. Here, then, are five reasons why the Z4 is another tick against his name.
1. Stiff Body In White
The basic bodyshell is 25 percent stiffer than before. Vital, said Krusche, for the entire driving experience. This torsional rigidity is the starting point, the vital gear in the cog. Without such a good starting point, he said, it is impossible to make cars drive well.
‘It is a big step down if the tolerances are too great.’ You can’t turn a fundamentally bad car into a good one by tweaks alone.
2. 3 Series front axle
The new Z4 uses the 2-joint front axle from the E90 3 Series (and also the various iterations of 1 Series). It’s vital, said Krusche, not least for improving feedback to steering.
With it, BMW can independently tune directional stability, steering feel and lane change stability. Curing a major flaw of the E85 Z4: its wearisome camber steer.
The rear axle, incidentally, is a development of the old Z4 (and is also on the X3). ‘There was no reason to change it,’ said Krusche.
3. Axially parallel layout electric power steering
The new Z4 also uses the axially-parallel EPAS system from the 3 Series. It means the engine isn’t sat on the steering column, so mass is reduced and a purer feel from the road is allowed. The electric motor is in parallel to the steering rack.
The EPAS system has also allowed Krusche to tune the frequencies from the road surface. Basically, you want to isolate high frequencies, but allow through low frequencies. Cumulative learning from the old, oft-criticised Z4 EPAS has allowed BMW to do this.
‘You can vary steering torque with the switch in the car,’ said Krusche. It means it can be (over) light in normal mode, meatier in Sport +.’
He’s also tuned it so there is no resistance for when you need to make steering corrections – tidying up snap oversteer, for example. ‘We also vary the feel for when you come to the limit, adjusting the Servotronic function for more feedback.’
4. Greater understanding of run-flat tyres
The E85 Z4 was a run-flat pioneer, and earned much criticism for being so. The tyres’ necessarily stiff sidewalls, and greater weight, both counter ride fluidity. Almost a decades’ learning, plus BMW’s close collaboration with tyre maker Bridgestone (the rubber’s bespoke for the new Z4) mean big improvements.
The evidence of this learning is illustrated by driving the E60 5 Series alongside the newer E90 3 Series, for example. But for greatest contrast, feel how the E85 and E89 Z4s deal with impact harshness and sudden surface imperfections.
Krusche makes a further revelation here, though: again, close work with the Body In White team has led to yet more improvements. By working out the intricacies of where run-flats need compliance in the structure, and where they’ll benefit from extra stiffness, BMW’s been able to tune and filter the natural frequencies of the bodyshell to dramatically improve ride quality.
It’s all about iterative understanding, he said.
5. Change in BMW setup philosophy
Since the 1 Series Coupe, BMW has subtly tweaked its basic chassis setup to improve comfort. Spring rates are slightly softer, and dampers a little stiffer. This has been influenced, again, by knowledge from the characteristics of run-flats.
The secret to doing this well, says Krusche, is in damper tuning. By playing with internal baffles, the size of the holes within them, the rates of flow between the three internal champers – goodness, even the material of the plunger on the strut! – depth is engineered in. Fine art? Call it black magic…
Despite all this, though, Krusche says he doesn’t get the final sign off. It’s always down to the BMW Board – who, at least thrice a year, will drive test cars and give the final say-so.
Krusche can only do so much. The final Z4 we drove on the launch was not one chosen by him, but the good Dr. Ings. You have to say, all have not done a bad job…
NEW: BMW Z4 photo stream on Flickr March 21, 2009
Posted by richard in : Uncategorized , 3commentsWant to see what I’ve been up to on the BMW Z4 launch? Well, check out my Z4 photo stream on Flickr.
And be sure to come back here over the next few days, as I plough through all my notes and feed back to you…
… clicking on the images should give you a taster, though!
Pre-launch impressions: BMW Z4 2009 March 21, 2009
Posted by richard in : Uncategorized , 1 comment so farSitting on the plane, going through the press information for the Z4, writing this, I’m really rather intrigued.
See, I have a fair impression of what this car is going to be like. Fast, very crisp and agile. Sublimely cultured and smooth. Bigger and more grown up than the old one. And, vitally, smoother riding.
I don’t expect it to have lost the original’s alacrity and rear-balanced precision. Indeed, I expect this to be enhanced, as there’s surely no way the new one can tramline and follow the road surface as badly as the old?
And, with the improvement in ride quality, it’s going to be a much easier car to drive on rough surfaces.
There should be a sat-back, powerful feeling, judging by how close the seats are positioned to the rear axle. That will be enhanced by an engine I adore – the 3.0-litre twin-turbo. 306bhp, 62mph in 5.2 seconds… it’s just dawning on me how fast this is likely to be.
Negatives? Well, I reckon they could have done more with the interior which, apart from a Z8 style centre console, lacks the special style of Audi’s TT. The instrument panel also looks a bit cheap, still, despite apparent improvements elsewhere.
Back to ride, though. They’ve got to, got to, have improved it, surely? In fact, I can guess they have. The press pack tells me the optional electronic damper’s stiffest setting is only as stiff as the old car’s standard set-up…
I have doubts over the price, though. The sDrive35i I’m driving today is £4400 dearer than the sDrive30i – that car’s almost as fast. What are the benefits of the sDrive35i? I’ll be grilling them to find out the intricacies.
My aim now is to always record these pre-impressions, then to see how the reality fares. You can follow my thought processes, and any preconceptions I take into the road test, for a more accurate representation of how a car actually is.
