The first North American Ford to get torque vectoring control will be the 2012 Focus. Ford is pitching the system as a safety- and performance-enhancing addition that helps the car "carve through turns like a downhill skier." We're not convinced.
First, we should understand how the system works. According to Ford, the torque-vectoring (TV) system works by applying "slight braking force" to the drive wheel most likely to slip during throttle application. In our experience, that's typically the inside wheel when exiting an aggressive turn. Ford claims the system's action is "imperceptible" to the driver, simply improving handling.
In reality, the TV system is an alternative to a limited-slip differential, leveraging existing wheel speed sensors and electronic brake control borrowed from the stability control system. How does the TV system mimic the presence of a limited-slip diff? By controlling the amount of wheelspin across the open differential through brake application, preventing the "one wheel peel" open diffs are known for.
The end result? "[A] Focus class-exclusive feature that serves as a confidence-builder for novice drivers, while pleasing enthusiasts with added control when cornering," says Ford.
All well and good so far, right? Not really. In our experience, TV systems' interferences with driver inputs are not only not imperceptible, they're downright annoying. In practice, TV systems aren't predictable in their engagement, often over-limit wheel spin, and generally serve to slow the car and make it harder to drive at the limit--especially when compared to the system they're replacing: limited-slip differentials. Even BMW doesn't get this right, so we don't expect anything special here.
Limited-slip diffs have their downsides, too, particularly in front-wheel drive cars. The first-generation Mazdaspeed3 is an excellent illustration: torque steer galore. But unlike computer-driven electronic nannies, the action of a limited-slip diff is mechanical, and therefore predictable. Don't hammer the gas until the wheel is straight, and expect some tug if you do--particularly over bumpier asphalt. Plan for it. Use it.
You can't do that with torque vectoring. You can't plan for that dab of brake on the inside wheel, which, depending on the surface, can actually reduce front-axle traction even further, particularly if you're already at the lateral limit, leading to understeer where an open diff wouldn't. Further, it taxes the brake system harder, applying the already-overworked front brakes during acceleration as well as braking, leading to reduced times before brake fade begins.
Catch the official announcement on page two.