SUSPENSION

If roads were smooth, cars wouldn’t need advanced suspension


When it comes to discussing cars, talk will often focus on horsepower, 0-60mph sprints and outright top speed, but a Jaguar’s suspension is a crucial component of its DNA.

There’s a finely judged compromise between a car’s ride quality – its ability to smooth out bumps in the road – and its handling. In today’s modern Jaguars, though, the continuous evolution of high-tech suspension has reduced this compromise to a minimum.

Pete Davis, Jaguar’s manager of Vehicle Dynamics, started working on Jaguar’s suspension systems back in 1986. Today, subjective feel and objective measurements are combined with the speed and convenience of computer-aided engineering (CAE). “Computer modelling helps you avoid fundamental flaws,” Pete says. “It allows us to quickly achieve a basic set-up that is sound and capable. That gives us more time to make the best of our human skills.”

All of today’s Jaguar models benefit from exceptionally stiff bodies, which allow the suspension to be tuned more accurately. Jaguar’s core suspension design – wishbones at the front and rear – is familiar to the XF and XK models, and the all new XJ. “The XJ is the sixth time we’ve tuned this configuration,” Pete says. “We understand how the components interact and how to tailor them for each model. It’s an evolution of constant small, incremental steps that together make a huge difference.”

This process is crucial to defining a car’s ‘Jaguar-ness’ – a favourite subject for Mike Cross, chief engineer of vehicle integrity. “There are basic metrics we apply to every model,” he says. “It really is possible to show on a graph how a Jaguar feels.” Equally, each Jaguar’s physical properties alters its suspension dynamics. “Each car has a distinct character, with a common DNA,” Mike adds. “The XK is the most overtly sporting, while the XJ is the most comfortable and refined.”

This is where the holy trinity of CAE, Pete’s objective analysis and Mike’s development experiences become crucial to suspension tuning. Much of their work focuses on the springs and dampers.

Softer springs provide a cushioned ride at the expense of good body control. Harder springs offer excellent body control, but a harsh ride. Finding the right balance is crucial and much depends on the role of the car. The front springs on the XKR, for example, are 38 per cent stiffer than on a standard XK, reflecting both the increased mass of the supercharged engine and the XKR’s sporting focus.

The dampers manage the spring’s kinetic energy, minimising the awkward bouncing motion from bumps. The XFR, XKR and new XJ employ Jaguar’s Adaptive Dynamics with electronic damping – a continuously variable system that analyses a car’s body motion and steering inputs 100 times a second, before tuning the damping response to match both the road surface and the driver’s driving style. It’s like having a million old-fashioned dampers under the bonnet, and means that Jaguar drivers can now define their car’s set-up according to the conditions, or even their mood.

“On the previous system we had 81 variables,” explains Pete. “Now we measure 890 parameters just for the damping, and each of them has to be individually tuned. But the system has allowed us to broaden each car’s range of abilities.”

Through it all, the Vehicle Dynamics team must ensure that every Jaguar retains its soul. “Electronics allow us to make the car more capable, but it must always feel authentic,” says Mike. “A Jaguar should never feel artificial. Getting the right blend between performance and comfort doesn’t get any easier, but that’s why this job is so interesting – and so rewarding when you get it right.”

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