THE TEST DRIVER
It takes a special kind of driver to push a 510PS (503bhp) prototype Jaguar XFR to its limit around a test track while critically assessing the subtleties of its driving dynamics. But it's this attention to detail and unwavering focus that gives a Jaguar its defining character.
"If you can't get passionate about a project like the Jaguar XFR then you're in the wrong job," grins Jeff Mitchell, technical specialist in Jaguar's Vehicle Integrity department. "We're all experienced vehicle assessors here. You've got to be able to drive a car accurately and consistently while maintaining a good understanding of the driving dynamics you want to achieve. We refer to the Jaguar's driving character as ‘duality' – blending a style that makes sure the car isn't hard to drive, but is rewarding in situations where you can extend it."
Although dry-handling proving grounds at Gaydon and MIRA in the UK are used extensively during development, 'extending' a high-performance Jaguar prototype typically involves German autobahns and the legendary 13-mile Nürburgring Nordschleife circuit.
"For handling and performance, the car will be fully instrumented to record data across the board on such things as steering input, body acceleration and brake pressure," says Jeff. "If we highlight a handling behaviour that we want to improve, we can identify it by looking through the data traces trackside. That instrumentation enables us to re-calibrate, so the car behaves with the dynamic quality we defined at the start of the process."
"With XFR, like any new model, we start off by defining what we want it to be. Obviously, with a 5-litre supercharged engine it was going to be pretty special in terms of performance capability. But the only way for it also to be composed, agile and have that edge, is to blend the damping with the steering, the active control diff with the transmission. Vehicle Integrity looks across all those attributes – all the things you feel, touch and interact with as you drive the vehicle."
Clearly, there are many technical specialists developing each aspect of the XFR, but it's the role of Jeff and his colleagues to keep a focus on that duality, to ensure every part meets and complements the defining character.
"We'll look at pedal weighting and steering effort – the response you get from the car for any given input. We'll also measure powertrain sound quality during acceleration, at cruise speeds and judge the proportion of that sound to the demand you put on the throttle."
Alongside its physical presence and its performance, XFR also boasts a wide range of innovative technical attributes.
"The XFR, along with the new XKR, introduces active differential control and continuously variable damping technology to the Jaguar range," says Jeff. “The more usual approach in this segment is to use electronically braked differentials, but that's very different from our system. Rather than simply using the brakes to stop the wheels spinning, the XFR's diff varies the amount of torque across the rear axle. Rather than curtailing acceleration performance, it supplies as much power as it can. We tested these systems under controlled track conditions and on real roads."
Perhaps the most elegant expression of how Jeff and his team have blended systems to create the car's character is the switch from standard to dynamic driving mode via the JaguarDrive Selector.
"When you shift up to dynamic mode, all the systems, such as damping, active diff control and throttle response, are switched in the same proportion to a new dynamic level that gives the car that Jaguar edge," says Jeff.
"We defined a car that's composed and easy to drive, but hugely rewarding when you wanted it to be. We're very proud of the result."
JAGUAR TEST VENUES
Situated in Swedish Lapland, the Arjeplog test centre provides a variety of courses laid out on land and natural lake ice – perfect for stability and traction tests. Although cold chambers play their part, they cannot tell you how a car behaves after a sub-zero night with a 30mph wind packing snow into every crevice.
Death Valley, USA
In the hottest place in North America dozens of channels of data are recorded in a variety of heat tests. For example, the car is ‘soaked' to temperatures of 50C, then the air-conditioning is activated and its efficiency measured. The heat affects air intake too, so engine and transmission performance is assessed.
Gaydon test track, UK
The track at this Jaguar facility is predominantly used for higher-speed vehicle refinement tests such as assessing wind and road noise and some elements of ride and handling.
Gaydon test chambers, UK
Extremes of temperature can be recreated in Jaguar's test chambers. Here, tests on engine start, idle, air-conditioning and demisting at varying temperatures can be turned around in a quicker and more cost-efficient way.
MIRA proving ground, UK
On this facility's dry-handling circuit the car can be driven beyond its limit in a safe environment. Its wet-handling circuit is used to assess stability systems, the active diff control system and tyres.
This high-speed circuit has been used by Jaguar for more than a decade to test dynamics and durability. Test drivers are also able to assess high-speed performance on nearby autobahns.
Jaguar has an environmental chamber at its design, research and development centre that can deliver high solar loads. Air-conditioning and engine management systems are put through extreme cycles devised to stress-test the system.
Tyre rigs won't tell you how a tyre handles, so Jaguar uses this Pirelli-owned facility near Milan to find out. It provides well-controlled water flow across asphalt of a known grip level.
[Issue 1, 2009]