![]() Audi’s Sport Differential helps the nose-heavy, four-wheel-drive S4, S5, and S6 turn in like rear-drivers.Īutomakers insist that torque vectoring will always be a niche offering, but as the technology has matured, it’s found its way into more diverse applications such as the four-wheel-drive Nissan Juke and the aforementioned Focus RS. The torque-vectoring differential is why the massive BMW X5 M and X6 M are more ridiculously entertaining than they have any right to be. Torque vectoring came to production cars via rally-bred racers such as the Mitsubishi Evo, but today it’s most commonly found in expensive, overfed, four-wheel-drive vehicles with a performance pretense. Instead, the partially meshed overdrive gears provide a push, like paddling harder-not faster-on one side of a canoe. Because the clutches don’t fully engage, the outside wheel doesn’t actually spin faster. When the computers decide to divvy up the torque, clutch packs connect the overdrive gears to the differential output, varying the clamping force to adjust thrust between the left and right wheels. ![]() Proper go-fast torque vectoring requires at least one overdrive gear in the differential (though often there are two) capable of spinning the wheels faster than if they were driven through a conventional diff. But it doesn’t take a race engineer to recognize the paradox in using the brakes to go faster. Automakers use this setup because it’s lighter and cheaper than ponying up for the more complex hardware while still creating a useful yaw moment. Brake-based systems selectively squeeze individual brake calipers to slow the inside wheels and increase torque to the outside wheels in turns. We should note the distinction between the differentials we’re discussing here and brake-based torque vectoring, the dollar-store variety that’s increasingly found on economy cars and crossovers. Those attributes should translate to a more controllable car, higher speeds in corners, and faster lap times. ![]() In theory, torque vectoring helps a car corner with reduced steering lock and less understeer. With unequal torque between the two sides, the resulting yaw moment (torque about a vertical axis) either encourages turn-in or stabilizes and straightens the car, depending on how the torque is distributed. Controlled by sophisticated electronics and fitted with complex gearboxes, these high-tech diffs are placed on the drive axle to regulate thrust between the left and right wheels. Torque-vectoring differentials are capable of much more, though. Whether it’s an open, a limited-slip, or a torque-vectoring example, a differential allows any wheel that’s connected to the powertrain to rotate independently. As a car rounds a corner, its tires trace four distinct arcs with four different radii, so each wheel turns at a different speed. Like all differentials, the torque-vectoring unit’s first responsibility is to reconcile speed differences between the drive wheels. Where the Magic Happens: Bolt-on torque-vectoring modules from British driveline specialist GKN transform this otherwise-normal open differential into a corner-carving tool. ![]()
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