Ford Focus RS

A charged four-cylinder engine increases performance in the hot-hatch and all-wheel drive improves traction and dynamics

Ford turned to GKN for the all-wheel drive system that would deliver the driving characteristics it wanted. The Focus RS uses the same base Twinster technology as the Range Rover Evoque, but it’s been modified to cope with the specific demands of the hot-hatch.

The system is based on twin electronically controlled clutch packs on each side of the rear drive unit which manage the front-to-rear torque split, and also control the side-to-side torque distribution at the rear axle. The control unit continuously varies the front-to-rear and side-to-side torque distribution to suit the driving situation. The system monitors inputs from multiple sensors 100 times per second.

Johnson says: “During the middle of a corner, the system transfers torque to the back end of the car, but not only to the rear, it transfers it to one side of the car, the outside. This then helps you to turn in, minimising understeer, allowing you to carry the speed through the corner and exiting more quickly.” 

Although officially a maximum of 70% of the drive torque can be diverted to the rear axle, it’s dependent on the situation, so in certain scenarios that figure can jump to 95%. At the rear, up to 100% of available torque on the axle can be sent to each wheel, and it can be switched from one side to the other in just 0.06 seconds.

What was challenging for the all-wheel drive system was the introduction of an overspeed function. The back end of the car runs 2% quicker than the front, so the back end is constantly trying to overtake the front, which helped achieve the dynamic targets, giving a livelier feel. In the first instance the clutch packs couldn’t cope and broke, along with some of the bearings, according to Johnson.

Weight increase because of the all-wheel drive is minimal. Johnson says the gain is 54kg, with total vehicle weight at 1,599kg in a length of 4,390mm. The Mercedes-AMG A45 weighs 1,555kg and the Audi RS3 is 1,595kg.

But Johnson and his team also wanted to introduce some fun elements to the RS, which is why launch and drift modes have been included. The launch mode is a little disconcerting; selecting the function, putting the car into first gear, applying full throttle and then dumping the clutch. It feels a little counter-intuitive, but is the fastest way to hit 100km/h.

The drift mode is a specially developed calibration of the all-wheel drive system that modifies the torque distribution to help the driver achieve controlled oversteer drifts. Both damper and steering settings are set to normal, providing enhanced control through smoother load transfers and lighter steering inputs.

But the mode would have been a hidden feature had it not been for Raj Nair’s input again. Johnson says: “We knew that we wanted the car to be able to drift, that was one of the reasons why we chose this system. In February last year, we had a drive with Raj and we showed him the trick. I said we’d put it at the back end and then when drivers discover it they’ll be amused. But he said no, you need to advertise it, you need to put it at the front.”

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