Differential (mechanical device)
An open differential (OD) is the most common type. It is also the least expensive. An open differential allows the vehicle to go around corners without dragging the outside wheel. However, power is transferred to the wheel with the least amount of traction (grip on the road). If that wheel is on ice or other slippery surfaces, the vehicle will not move forward and the wheel with the power will simply spin. In vehicles with two-wheel drive, if they have an open differential in effect they have only a single drive wheel. In four-wheel drive vehicles using open differentials (usually standard from the factory), only one wheel on each axle powers the vehicle. Advantages include seldom breaking an axle, less tire wear, and they are free as most new vehicles come with open differentials.