Bentley's engineers are going all out to create a top-drawer limousine in the new Flying Spur
There's nothing like a Scandinavian winter for testing prototypes. Icy, empty roads and sub-zero temperatures make the perfect car development laboratory.
That's why Autocar is hitching a ride with a team of Bentley engineers as they fine-tune the new Flying Spur saloon in the final months before production starts in May.
We're riding in a completely undisguised engineering validation car, known as a VFF prototype, which nosed through the gates of Crewe minutes after the first pictures of the luxury four-door were made public a couple of weeks ago.
VFF prototypes are built about nine months from production, and represent the last but one stage before the 'Zero Series', final production-standard cars, ship to customers. So being a way off production, there's still plenty of engineering to perfect.
The Spur is about 80 per cent new and features a fresh upper body and structure aft of the A-pillars, including expensive-to-tool items like the door inners. Only the windscreen and A-pillar angles have been carried over, albeit restyled. And there's a new interior, including front seats borrowed from the Mulsanne.
It may seem surprising that testing continues apace, just three months before the first customer cars are delivered. But the bulk of the Spur's vital functions are computer-controlled and the code can be fine-tuned late in the production cycle.
"We're able to hammer out the details and tune what we want pretty much weeks up to production," says project director Ken Scott. A Bentley veteran of 27 years, Scott started as a Crewe apprentice. He's leading today's activities and a team of four engineers and half a dozen back-up staff with infectious enthusiasm.
The team's combined engineering experience adds up to 102 years. Scott has flown into Stockholm to join his team, who have been on tour with the 616bhp, twin-turbo W12-powered prototype. They've been pounding autobahns on high-speed testing, before heading north through Denmark to Sweden for a stint of cold-weather evaluation.
Nor will the pace slacken. The next step takes DK62 FSU back to Munich for a top-level management appraisal before it is air freighted to the US. As you read this, the Spur should be on rural roads in California.
Our time, however, will involve a chilly, 400-mile dash westwards to Oslo in neighbouring Norway, with every engineering component, fit-and-finish item and driveability feature on watch. Scott takes the wheel for our first stint out of Stockholm, and the watching brief for the first 60 miles or so is the heating, ventilation and air conditioning (HVAC) system, whose calibration in cold weather is still to be finalised.
This much was evident on the drive north from Germany, the prototype misting the windscreen as the temperature plummeted. So the team has downloaded computer code from a shoebox-sized data logger spliced into the wiring loom and bolted into the boot. "We can grab all the data we need from the car's own system. We don't need extra instrumentation at this stage," says Nick Burns, Scott's second in command and the HVAC expert on this test.
Control code for the air-con has been emailed to Crewe and a revised version sent back overnight and installed for evaluation today. The problem still isn't fixed, though, and the driver's side of the windscreen is continually fogging up. Burns reckons he knows what the problem is: the blower isn't shifting enough warm air to the humidity sensor sited in the base of the rear-view mirror. As a result, the dryer in the air-con is pumping air with too much moisture, which is condensing on the inside of the screen. Another fresh batch of code will be reloaded overnight in a bid to fix it.
Fixing the air-con is a relatively routine task, but it has to be done to satisfy the demands of customers, particularly in China. The whole Flying Spur programme has been centred around Chinese market needs. It's the single biggest market for the Spur and, over the model's life, 60 per cent of production will head there.
Early in the project, in spring 2011, Bentley researched the Spur with dealers in Beijing, who pinpointed three major areas for improvement: more cabin refinement, less exhaust noise and new infotainment for the rear-seat passengers. Bentley then broke new ground, returning to Beijing in autumn 2011 with an early Spur engineering prototype featuring improvements to all three.
"They were speechless," says Scott, "No one had done that before – let them influence the car and then comment on progress in a real prototype."
Inside the cabin, the hush is noticeable, especially the subdued exhaust warble. Bentley's internal benchmark quantifies cabin noise as the ease with which conversation can flow between front and rear occupants. "We've got an eight per cent improvement," says Scott.
Calming the cabin has centred on cutting wind noise with acoustic glass, employed in a Bentley windscreen for the first time. Engine noise has been subdued by muffling the induction and exhaust notes. During our cold-weather test, the main cabin noise comes from the road because of the chunky winter rubber fitted. "Summer tyres are much quieter," says Scott.
There is also unwanted wind noise from the driver's A-pillar, which will be fixed as build standards improve closer to production. "We've designed new, better sealing. This early build is not quite sitting right in the door shut, but it'll be ready for production," says Scott.
European and US demands for the Spur have focused on improving high-speed stability and on-centre steering feel for the driver, which backs up the more muscular styling.
The new, broader-shouldered look pushes the body out by an extra inch or so and the tracks have been widened by 20mm at the front and 35mm at the rear. Longer front stub axles demanded retuned springs and dampers, which opened up the possibility of refocusing the Spur as a 'limousine' with a softer chassis tune in place of its predecessor's firmer 'four-door Continental' theme.
"Now the front air springs are 10 per cent softer and the rears 13 per cent," says chassis manager Andrew Unsworth, "but we've adjusted the damping to be a little stiffer to compensate."
To absorb the initial impact on bumps, Bentley has also slackened off the bushings; some are as much as 38 per cent softer. But the chassis is not all about comfort. The Spur's steering is more purposeful and heavier weighted.
"We've completely retuned the ZF steering rack with a new boost curve aimed at improving feel around the straight-ahead," says Unsworth. He's confident that the final set-up fits the brief of a more stable cruise, yet greater ride comfort.
My guess is that the ride will prove more cosseting and quieter than before on UK roads, but body control might suffer a little. On balance, that probably makes sense for the target audience, although it seems to weaken the link between the Spur and Bentley's sporting heritage.
But as Scott shrewdly identifies: "Once you have the fundamentals right, it's easier to make a stiffer and sportier chassis for markets if they want it, rather than the other way around."
As our test route heads towards the Norwegian border and our final destination of Oslo, there's some more give and take and stop-start driving, where driveline refinement is not quite as smooth as it should be. Revised computer code will be loaded into the ECU that controls the ZF eight-speed gearbox to better slur some of the downchanges and refine the drivetrain.
This is also the perfect opportunity to slot into the comfortable rear seats and get to grips with the new rear-seat entertainment package developed to cement the Spur into its new role as a luxury limo. Bentley is the first company in the Volkswagen Group to use a new Bury touchscreen tablet that controls the headrest-mounted infotainment screens.
The palm-sized RST – rear-seat tablet – works effectively and also allows the rear passenger to control the satellite navigation, a useful feature for passengers to set the destination for the chauffeur up front, and adjust the air-con. It even relays the vehicle's speed to the rear cabin.
Whether that was on the wish list of the all-important Chinese customer, I don't know. But it is just one of hundreds of detailed revisions to the new Spur that suggest Bentley's new saloon will be genuinely much improved.
We'll find out for sure in May, when the first test cars become available.
Bentley Flying Spur
Price £141,000 (est); 0-62mph 4.6sec; Top speed 200mph; MPG 19.2mpg (combined, est); CO2 434g/km (est); Weight: 2475kg; Engine W12, 5998cc, twin-turbo, petrol; Engine layout Front, longitudinal, 4WD; Power 616bhp at 6000rpm; Torque 590lb ft at 2000rpm; Power to weight 248bhp per tonne; Specific output 102bhp per litre; Gearbox 8-spd auto; Length 5295mm; Width 2208mm; Height 1488mm; Wheelbase 3065mm; Fuel tank 90 litres; Range 378 miles (est); Boot 475 litres; Front suspension Double wishbones, air springs, anti-roll bar; Rear suspension Multi-link, air springs, anti-roll bar; Brakes 405mm ventilated discs (f), 335mm ventilated discs (r); Wheels 9.5Jx19in; Tyres 275/45 ZR19;
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