An open end The simplest and most common unit is the open differential, called that because the wheels can always turn independently of each other. Its main drawback is that if one wheel doesn’t have traction, such as if it hits ice, it still gets lots of power. It spins helplessly, and you go nowhere. To help with traction loss while you’re driving, all new vehicles must be equipped with traction and electronic stability control. These use sensors from the anti-lock brakes to determine if one wheel is turning faster. It then reduces engine power, or brakes the spinning wheel, or both, to get things under control.