It may come with a licence disc and number plates (and available from your local Ford dealership later in 2019), but this is as close to a sophisticated off-road racer as a production vehicle can get. You may have read my driving impression of the Ford Ranger Raptor in the Australian Outback a little while back. But in this feature, we reveal how Ford’s engineers managed to change a standard Ranger into a Bushveld cruise missile … that can still comfortably ferry the kids to school.
Off-road racing vehicles don’t generally have much in common with production cars. They may sport recognisable (composite) body shells but, underneath, they’re all space frames, racing suspensions, highly tuned engines and bespoke drivetrain systems adhering to the regulations of the relevant race series. The cost of these vehicles can easily run into millions, making them prohibitively expensive to buy. Add the fact you need a trust fund to run such a vehicle and these cars are far out of reach of most enthusiasts.
However, this changed when the Ford F-150 Raptor was launched in the United States back in 2009, its big V8 offering off-road racing potential right from the showroom floor. The latest F-150 Raptor employs a 3,5-litre turbopetrol V6 delivering 336 kW and it could theoretically compete in the Baja 1000 desert race. According to Hermann Salenbauch, global director of Ford Performance, a similar goal was set for the Ranger Raptor, with the intention for it to become a fully fledged member of the top-echelon Ford Performance stable.
According to Damien Ross, chief programme engineer, the decision was made early in the programme to use a diesel powertrain because it suits the T6 (Ranger) platform and resonates with Ranger buyers. The most powerful engine in the Ford stable for this platform is a brand-new 2,0-litre, biturbo-diesel (low-pressure, fixed-geometry turbo and high-pressure, variable-geometry turbo) engine delivering 157 kW and 500 N.m. Interestingly, it has an eight-litre oil capacity to deal with high-performance and production-vehicle service intervals.
Disappointingly, on paper, this results in a power-to-mass ratio of just 68 W/kg which is much lower than that of the F-150 Raptor (132 W/kg) or a competitor bakkie such as the Amarok V6 (76 W/kg). It was therefore crucial to make the most of the available power by opting for a closely spaced, multi-ratio transmission.
Ford co-developed the 10-speed transmission with General Motors and it’s used in a variety of applications, including the Mustang. In the Raptor, with its narrow range of peak power, 10 gears make it possible to stay close to the peak power at all vehicle speeds. Incidentally, the part-time four-wheel-drive system, with transfer case, low range and diff lock, is from the base Ranger.
To dissipate the high heat associated with racing, Ford added an all-new disc arrangement (332 mm in diameter all-round and ventilated), ditching the Ranger’s rear drums.
Chassis and suspension
Simon Johnson, lead engineer on Raptor vehicle dynamics, was given the challenging task of creating a chassis both capable of handling off-road abuse and one that could provide acceptable on-road behaviour. And all this while staying within a tight budget. The fact Johnson had also worked on the standard Ranger and Everest’s dynamic abilities was useful.
The Raptor’s ladder-frame chassis is based on the Ranger front-end and Everest rear, with the main reason being the addition of a Watt’s linkage axle, beneficial for axle control at speed (with close to straight-line vertical axial movement but no lateral movement allowed). This is where the similarities end, though. The Raptor’s track width is 150 mm greater (in addition to a 50 mm increased ride height) with extra bracing added to elevate rigidity in torsion and bending moments. This meant the front double-wishbone suspension received new A-arms with optimised geometry (20% more travel than on the Ranger) and Fox double-tube racing shocks (more about the shocks later).
At the rear, Johnson removed the leaf springs and altered the ladder frame so the Fox coil-over suspension could be mounted outside the ladder frame (30% more travel than on the Ranger) connected to the wider rear axle. There is no pathway for the exhaust to exit at the rear and it is therefore cut off short under the body. According to Johnson, the rear section of the chassis was a more expensive solution than was initially planned but, after senior management drove a prototype vehicle with this setup, he got the go-ahead.
The Fox suspension is state of the art, with the double-tube arrangement sporting oil-bleeding holes in the inner sleeve. When the shock is compressed, these holes get sequentially closed as the piston moves down; this essentially increases the damping rate in steps as the shock is compressed, resulting in a compliant ride during small movements but, because of the increased damping, it is almost impossible to bottom out the shock at maximum travel.
According to Johnson, who calibrated the spring-and-damper settings, the bump stops are seldom reached, preventing the mounting points from breaking. The sharp spikes in loads when the end-stops are touched are usually chassis breakers.
On rebound, the damping has a “hold zone” keeping the suspension compressed for longer after full compression to prevent bucking behaviour (also known as porpoising) after a big jump.
Simulations predicted suspension loads and these forces were validated by vehicles equipped with strain gauges recording loads on critical components. It was impressive to witness first-hand the kind of loads this suspension can cope with without showing strain. Interestingly, even the spare wheel’s mounting points were strengthened to cope with the added load strain.
Ford has a good working relationship with BF Goodrich and, like the F-150 Raptor, the company supplies the standard-fit rubber on the Ranger Raptor. For the latter product, BF Goodrich’s focus was on the construction of the tyre, as the compound already proved itself on the F-150. The suspension setup allows for a stiffer and stronger tyre construction also reducing rolling resistance, thereby easing fuel consumption.
The three-ply sidewalls are reinforced with a technology called CoreGard to prevent damage and, remarkably, Ford lost only one tyre during the whole development programme, testament to how tough these tyres are.
Another advantage is that, although the design features an aggressive tread pattern for off-road grip, it is still reasonably quiet on tar and also offers decent wet-road performance, according to Wayne Yount, senior product development engineer at Michelin.
Can you create your own Raptor?
The short answer is no, mostly because of the substantial changes you’d have to make to the chassis. Even if you buy uprated dampers, the geometry and mounting points are completely different from Ranger to Raptor. Although the ride-height increase of 50 mm is possible, it is tricky to widen the track by 150 mm. Spacers or off-set rims will place undue strain on bearings and suspension components never designed for these additional loads.
By raising a standard Ranger by 50 mm (and so too the centre of gravity), the roll-over risk is also greatly increased. Calculations show the 150 mm increase in track width actually lessens the Raptor’s roll-over risk compared to the standard Ranger.
According to Ross, if you tallied up all the changes made to the Raptor and attempted to replicate this on a Ranger, you’d end up spending a great deal more than the projected price difference between the two models.
Author: Nicol Louw
Original article from Car