Words: Robert Nichols
Photography: Robert Nichols
Published: July 6, 2016
I am completely and utterly astounded that there are not more Jaguars out on our roads these days. Ever since the brand rebooted itself nearly a decade ago leaving off traditional design and questionable reliability, their cars have been increasingly tempting. Take for example the bright white 2016 XF-S I was fortunate enough to pilot. Now in its second generation the model received a few enhancements fixing a couple annoying oversights and even injecting a more fun-to-drive feel that is all important in a vehicle with such deep roots in racing.
The other editors have thoroughly reviewed this model already and there is nothing to add about the way this car drives or the lovely noises it makes, so I thought I would take some time and figure out how Jaguar has made this car drive and handle so well by looking closer at the engineering and technology. I will endeavour not to sound like a professor giving a lecture, but some of the deeply techy explanations may get a bit academic.
One of the key performance impediments to every car ever made is weight. Weight slows your acceleration and top speed; it also forces you to slow down in a corner for fear your mass will overwhelm the level of grip provided by the tires. Weight also results in longer stopping distances, lower fuel economy and lethargic handling. Obviously if Jag wanted to build a “sporty” sedan they would need to follow the Atkins diet; carbs are the enemy after-all.
The key to keeping weight down was with the ample use of aluminum. Quite a lot of excess girth was trimmed over the outgoing model; 120 kg for Canadian models to be specific. That’s like losing a Kawasaki Z125 Pro motorcycle or a portly friend who thinks doughnuts are a type of fruit.
The term “all-aluminum” gets thrown around a lot these days and is a bit misleading; therefore Jag uses the more accurate term “aluminum intensive”. In the XF, aluminum is used to form the uni-body, hood and front fenders, but the cross beam and front end carrier have been formed out of even lighter magnesium alloys. The side panels, which are stamped out of a single piece of 6000 series aluminum, weigh just 6 kg each; I’ve eaten heavier meals.
Also exploiting the benefits of aluminum are the suspension towers, which are made from high-pressure die-cast aluminum. By using so much aluminum in key structural areas the 2016 XF has been made 28% stiffer and the body has even more torsional rigidity. So, now we need to know what torsional rigidity is and why we like a stiffer body, because that sounds unpleasant.
First let’s tackle torsional rigidity. Picture a car parked on a level surface. In this neutral state there is no torsion or twisting force being applied to the frame. Now imagine lifting just one wheel off of the ground, let’s say the front left tire. This simulates driving around a right hand corner. The pressure being applied to the frame is torsion.
A simple way to emulate this would be to lift a corner of your mattress and watch how if bends. If a frame was not able to remain rigid against this force the result would be a horrendously wallowing car unable to take a corner because the frame would bend rather than transfer the pressure.
By increasing the frame’s ability to resist this bending, engineers are increasing the car’s torsional rigidity. A more rigid frame allows the weight (pressure) to be transferred, from left to right while the vehicle is corning right. This transfers pressure to the right side suspension and tires improving grip and handling by keeping the tires flat against the road surface in a controlled and predictable way.
In times past, the body of a car was placed atop a frame and was a completely separate component. The frame would handle all of the ride and handling functions as well as providing all the stiffness. Modern cars use a unibody design wherein the body shell of the vehicle works as part of the frame to provide rigidity.
A body made of stiffer materials will help the car resist the tendency to flex and twist as the suspension encounters bumps or corners. So a stiffer car will be a better handling and safer vehicle.
There is also the benefit of a quieter cabin. Whenever something twists there is going to be some associated noise and/or vibration. Inside the cabin of a car, if the structure (frame or unibody) were to twist everything inside would twist, the dash, seat mounts etc. This would result in noise, and weaken the mountings for said pieces, which in turn would result in rattles or breakage.
Jaguar claims the 2016 XF is up to 28% stiffer which means the car as a whole is 28% better at resisting the twisting, and flexing forces encountered in day to day driving. A large part of this improvement is thanks to the use of aluminum. Compared to the mild steel used to make body panels aluminum is an inherently more rigid material. The switch to aluminum has greatly affected the car’s handling, performance, and safety. Yes, kilo for kilo it can absorb far greater (in some cases up to 50% more) crash energy. This means larger crush zones can be designed without the penalty of added weight.
Of course, the body and frame are not the only pieces of the performance puzzle. The XF uses a double-wishbone setup in the front and an integral-link out back. Because the structure of the vehicle is stiff, the suspension, which is mounted to the structure, is forced to react immediately to the various loads, be it cornering or hitting a pothole. The rapid response delivers a sporty and agile feel to the driver. Of course this could also result in a bumpy or harsh feeling, not unlike a go-kart with next to no suspension. To compensate for this characteristic Jaguar uses adjustable dampers (highly advanced shocks).
The XF suspension system, called the Jaguar Adaptive Dynamics System monitors the vehicle’s body movements 100 times per second and tire movements 500 times per second. The system uses algorithms that also take into consideration how fast the car is travelling and the mode the driver has selected (ECO, Normal, Sport and Dynamic) and uses this information to control valves in the dampers.
Inside the dampers there is a fluid. In this fluid, a piston travels up and down as needed. This is the motion you feel when you press down on a corner of the car. In order to control the speed at which this piston moves, the Jaguar system forces the fluid to pass through valves that can limit or increase the amount of fluid that can pass in a set period of time. By allowing more fluid to move (opening the valve) the suspension will feel softer and more comfortable. By limiting the fluids motion (closing the valve) the suspension will feel firmer and less forgiving.
It did not take long at all to appreciate all of this engineering wizardry out on the open road. The XF-S is a fun-to-drive mid-size sedan with definite sporting aspirations. The increased rear passenger space and updated infotainment have taken a good car and made it great. The advanced engineering has made it exceptional. Of course there are some who have absolutely no interest whatsoever in the more technical aspects of this car so to them we say just feast your eyes on some pictures. It is a very pretty car, isn’t it!
型号 Model: 2016 Jaguar XF S AWD
廠方建議售價 Base Price: $72,900
試車售價 Price as Tested: $78,300
軸距 Wheelbase(mm): 2,960
長闊 Length/Width/Height (mm): 4,954 / 1,880 / 1,457
車重 Curb weight (kg): 1,760
引擎 Engine: 3.0-litre supercharged V6
最大馬力 Horsepower: 380 hp @ 6,500 rpm
最高扭力 Torque: 332 lb-ft @ 4,500 rpm
波箱 Transmission: 8-speed ZF automatic
擺佈 Engine & Drive Configuration: Front engine, AWD
前懸 Suspension-Front: Double wishbone
後懸 Suspension-Rear: Integral link
油耗 Fuel Consumption ( City / Highway / Combined ) L/100km: 11.9 / 8.3 / 10.3
輪胎尺碼 Tires: P295/35R20