Sharpening the cat's claws

Turning the Jaguar XKR road car into a GT3 racer involves an almost total reconstruction and plenty of track testing. Time to bring in an expert…
By Johnny Mowlem

Over the past few years a plethora of GT3 cars has emerged as more and more international sports car championships turn to them either to bolster their grids or create a bigger performance divide between the GT and prototype classes. Witness what the Grand-Am Road Racing series and American Le Mans Series have done in recent times.

On top of that, there has been a real growth in championships solely aimed at GT3 cars, with the heavily subscribed international FIA GT3 series as the flagship.

As a result GT3 cars have gone from being largely the domain of one-make series such as the Porsche Supercup to a recognisable ‘brand’ of racing in their own right, with different makes of car competing against each other in a championship – often a handicapping nightmare for the series organisers!

Through my past factory links with both Porsche and Ferrari, I have had the opportunity to drive and/or race their GT3 cars, the staple of GT3 grids. But with the increase in GT3 popularity, ever more exotic brands have begun to show up on track, ranging from Ascari and Aston Martin through to Morgans.

Recently I got the opportunity to drive a GT3 car based on what – especially from a British driver’s point of view – was a very exciting proposition, the beautiful Jaguar XKR.

Now, for me, Jaguar is one of those brands that instils a very romantic and glamorous view of the best of British motor sport. This is probably because I am a sports car racer and as a boy I remember reading books about Jaguar’s success at the Le Mans 24 Hours and Stirling Moss’s daring exploits in ’50s Jaguars, not to mention the iconic ‘Silk Cut’ cars of the late ’80s which were dominating in world sports cars just as I was about to embark on a career that would lead me to the same form of racing.

It is said that by the time a boy turns 10 he has decided what his dream car is, and that stays with him for the rest of his life. For me it was a retired naval commander’s car that first sparked my daydreaming, when in the early ’80s I used to sit in the car park behind our little flat in Mallorca and gaze at a Carmen red series 3 V12 E-type 5.3-litre convertible. Of course, I didn’t know any of those details at the time. All I knew was that there was a really sexy-looking open-top two-seater sitting in the car park, which to my 10-year-old eyes looked like a real racing car and which also appeared to be a magnet for a stream of women, all significantly younger than the retired naval officer. Even at such a tender age, I already had a vague understanding of the importance of that fact!

But back to the modern race car. I got the opportunity to drive this very sexy-looking GT3 XKR at Snetterton, a circuit I hadn’t been to for ages but one that I’ve always enjoyed due to its nice mix of technical and fast corners. I’d mostly driven there in single-seaters in my early racing years, so it was going to be fun finding out what a racing Jaguar XKR could do. I was especially keen to compare it to the road-going version, which I’d been fortunate enough to drive on numerous track days for my personal sponsor, Lancaster Garages.

I’m often asked how much road cars vary from their racing cousins. Just to give you a basic idea, when a normal road-going sports car – regardless of its make – is turned into a GT racer, it really does involve a lot of work. In this instance, John Christie’s organisation chose to take an existing Jaguar GT3 concept and start again pretty much from scratch.

An awful lot of time, money and effort goes into converting a luxury road-going sports car into a GT racing car.

First, you take the basic chassis. In the case of the XKR this is an aluminium shell, which means that in road-car terms it is already extremely stiff, which is what you require in a racing car. Having said that, once you’ve bolted in the safety cage you increase the stiffness in the region of 50 per cent, so that shows you just how much stiffer a race car chassis is compared to the road car, with all the associated ride qualities. In the case of other road cars, the rollcage can sometimes add in the region of 60 to 70 per cent extra structural stiffness.

So, in simplistic terms, you’d be sat there with a chassis and then you apply whatever ride height rules exist for the series you want to compete in, taking into account how much rake you want in the car front to rear. You set your zero line for the car, normally as low as you can get it given the regulations you’re working to. Once you’ve calculated that, along with your allowed tyre and wheel dimensions, you can calculate your suspension pick-up points. You must take into account a whole bunch of variables that will influence your actual suspension geometry, such as roll centres, castor levels etc. Your pick-up points on your uprights and on the chassis will always try to fight each other during lateral and longitudinal movement, so how you control this geometry – such as the camber change on roll and the difference between the front to the rear of the car – will all impact on whether your car will handle well under braking and through corners.

Now that’s just the chassis and suspension and doesn’t take into account all the ancillaries such as air jacks, the fuel cell, brakes and calipers, as well as other drivetrain items such as the fact that in the road car the gearbox is attached to the engine and in the race car it’s attached to the rear axle, with the gearbox being a DTM Hewland six-speed sequential as opposed to an H-pattern box.

Also, although in aerodynamic terms a GT3 car doesn’t develop huge downforce, it is still able to run front splitters, dive planes and a rear wing to generate a fair level of downforce, especially compared to most road cars which develop little if any levels of downforce at normal speeds.

The key word in all this is ‘stiff’. The chassis is stiffer than the road car, the drive train mountings etc will all be solid with little or no rubber mounting, and the anti-roll bars and springs will create a roll stiffness in the race car some three to four times stronger than what you would experience in even the stiffest of road-going cars.

As you can imagine, this creates an aggressive environment when you’re in the car on track. Even though Snetterton is relatively smooth, the car will still bounce around a lot through the corners. In my experience this is something inherent to nearly all GT cars, and that feeling of pogo-ing through a corner on a trajectory with what often feels like imminent disaster on the exit is the black art that you need to master when lapping quickly in a GT sports car.

I keep this in mind as I belt myself in tightly and fire up the engine. The throaty roar makes me smile, and I engage first gear and ease the nose of the car, which feels miles ahead of where I am sitting, out of the garage and into the pitlane. The lack of steering lock (another big difference between race and road cars) becomes apparent as I can barely make the turn out of the garage without hitting the pitwall, but I just squeak it round and then start accelerating down the pitlane.

Once out on track I open up the throttle and the car leaps forward as I begin to experience all of its 500+bhp. Now at this point I feel I should point out that the main reason I’ve been asked to drive this car isn’t in order to write a nice article for the wonderful Motor Sport magazine. I’m here to do the job of helping sort out the car’s set-up, as it is brand new at this point. So although the basic package is very good, I’m expecting the car to need a lot of refining, both in terms of set-up and driveability. For example, I soon notice that the sequential shifting is very stiff and the gear lever throw is quite long. On upshifts especially I’m having to put my shoulder into it to make it shift accurately. This is an easy fix in terms of some work on the gear linkage, however, so I turn my mind to the car’s handling.

As I start to press on, the XKR reminds me of a live, wild Jaguar! It is an incredibly aggressive car over the bumps and a little slow to respond to initial steering inputs, especially into the faster corners such as Riches, the ‘Bombhole’ and Coram. Its traction is reasonably good, but it still wags its tail at every available opportunity and also tends to slide a lot in the rear at the exit of corners. I have enough horsepower that I experience some lurid yet entertaining slides exiting Coram in particular! Knowing this is fun but that it will eat my rear tyres, I pull into the pits. And after a sequence of successive pitlane visits to soften the high-speed bump in the dampers, lower the rear ride height and stiffen the front low-speed damping to reduce rear roll oversteer and help the front platform respectively, I find I have a much tamer Jaguar underneath me. It’s still not as refined as it could be – it’s obviously early days – but it is easy enough to drive that we begin to bang in some very quick and consistent lap times. The car is still a little too aggressive over the bumps, especially exiting the second-gear Sears corner onto the back straight, but it is great fun to drive.

In terms of driver comfort the car begins to feel as if it fits me like a glove and, as I suspected, I haven’t even thought about the big sexy radiator air vent on the bonnet, which I feared I might not be able to see around. Looking at photos of me in the car later, I am sitting incredibly low, but visibility once out on the track was never a problem.

I thoroughly enjoyed the experience of hammering a Jaguar XKR GT3 around a track and getting it more to my liking. But in answer to those people who ask what it’s like to drive a GT compared to a road car, even though this XKR was probably three or four times stiffer than any road car, if I were to drive it again I’d stiffen this baby up some more and really get it working through those fast corners!

Jaguar XKR
Engine: Front-mounted V8, 4.2-litre XKR supercharged DOHC
Power/Torque: 420bhp at 6250rpm, 413lb ft at 4000rpm
Gearbox: six-speed automatic
TyresFuel: 22.9mpg, 71-litre tank capacity
Acceleration: 0-62mph in 4.9sec
BrakesWeight: 1665kg
Price: £72,400 (new 5-litre version pictured)
Top Speed: 155mph

Jaguar XKR S GT3
Engine: Front-mounted V8, 4.2-litre XKR supercharged DOHC
Power/Torque: 510bhp at 6500rpm, 457lb ft at 4600rpm
Gearbox: six-speed Hewland DTM sequential
Tyres: f: Michelin 30/65-18 S8C, r: Michelin 31/71-18 S8C
Fuel: Endurance Quick Fill ATL fuel system, 108-litre tank capacity
Acceleration: 0-62mph in 3.9sec (est.)
Suspension: three-way adjustable InTrax dampers, XKR double wishbone front and rear
Brakes: f: AP 6-pot calipers on 375mm discs, r: AP 4-pot calipers on 330mm discs
Weight: 1240kg
Top Speed: 165mph (depending on gearing)