‘Twin­ster’ al­lows Ford’s hot hatch to chart a dif­fer­ent route

Evo - - 4WD MEGATEST -

WHAT MAKES THE FO­CUS’S ALL-WHEEL-DRIVE sys­tem dif­fer­ent is that, when drive to the rear is en­gaged, a small dif­fer­ence in gearing be­tween the front and rear axles (less than two per cent) over­speeds the rear wheels. They turn a lit­tle faster, load­ing the rear and giv­ing a rear-drive feel.

The key part in all this is the GKN ‘Twin­ster’ de­vice that takes the place of the rear dif­fer­en­tial. The prop­shaft to it is al­ways spin­ning, but the Twin­ster is only en­gaged when re­quired, at which point its twin wet clutch packs – one for each rear wheel – are ac­ti­vated. In steady-state run­ning they are open, dis­con­nect­ing the drive to the rear wheels, aid­ing econ­omy but also essen­tial be­cause the dif­fer­ence in gearing would con­stantly try to ro­tate the rear wheels faster than the fronts.

The Twin­ster also de­liv­ers one of the holy grails of driv­e­train func­tion: pure torque vec­tor­ing. The elec­tron­i­cally con­trolled, hy­drauli­cally ac­ti­vated clutch packs send the ap­pro­pri­ate torque in­de­pen­dently to each rear wheel based on in­puts such as steer­ing wheel an­gle, lat­eral ac­cel­er­a­tion, yaw and speed. The mo­ment the sys­tem senses rear-drive can help, torque is sent to the outer rear wheel. This speeds it up, ro­tat­ing the Fo­cus into the turn. Up to 100 per cent of the torque avail­able at the rear can be sent to one wheel.

Elec­tronic sta­bil­ity con­trol sys­tems typ­i­cally ma­nip­u­late a car’s bal­ance by brak­ing in­di­vid­ual wheels, whereas the Fo­cus’s sys­tem is en­abling rather than re­strict­ing, adding pos­i­tive torque rather than brak­ing force. The de­gree of torque de­liv­ered to the rear wheels, and thus the at­ti­tude cre­ated, de­pends on the se­lected drive mode, from neu­tral­ity in Nor­mal, to ap­pre­cia­bly rear-drive in Track, and ul­ti­mately gen­er­ous power over­steer in Drift.

En­gine In-line 4-cyl, 2261cc, turbo Power 345bhp @ 6000rpm Torque 347lb ft @ 2000-4500rpm 0-62mph 4.7sec (claimed) Top speed 166mph (claimed) Weight 1547kg (227bhp/ton) Ba­sic price £32,765 evo rat­ing

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