Differential (mechanical device)
A locking differential (locker) is able to lock the two drive wheels on an axle together. The advantage is that both wheels have power at all times. The disadvantage is that turning is much more difficult since both wheels must turn at the same rpms. So most lockers must be disengaged when making sharp turns. Lockers can also present the driver with some dangerous situations. For example, when traversing a slope (going crossways) if one drive wheel loses traction both lose traction and the vehicle may slide sideways down the slope. Drivers are often warned not to traverse a slope if the surface is loose or slippery. Lockers may be switched on or off mechanically, electronically (e-locker) or using compressed air (air locker). Lockers are desirable on off-road vehicles but are usually not useful on streets and highways.