steering system, in automobiles, steering wheel, gears, linkages, and other components used to control the direction of a vehicle's motion. Because of friction between the front tires and the road, especially in parking, effort is required to turn the steering wheel. To lessen the effort required, the wheel is connected through a system of gears to components that position the front tires. The gears give the driver a mechanical advantage, i.e., they multiply the force he applies, but they also increase the distance through which he must turn the wheel in order to turn the tires a given amount. Various types of gear assemblies, none with any decisive advantages over the others, are used, although some manufacturers prefer a rack-and-pinion system. In faster, heavier cars the amount of force required to turn the tires can be very great. Many of these cars use a power-steering system. The system contains a hydraulic booster, which operates when the engine is running and supplies most of the necessary force when the driver turns the wheel. When a vehicle turns at a rate exactly proportional to the rate at which the steering wheel is turned, it is said to have neutral steering; if it turns at a slower rate it is said to understeer; if it turns faster it is said to oversteer. While any vehicle can react in any of these ways under extreme conditions, most automobiles are built to understeer. Racing vehicles are often designed for neutral steering; few vehicles are built to oversteer, since this is considered hazardous by many authorities. As a safety feature in many modern cars the column on which the steering wheel is mounted will collapse if the driver is thrown against the wheel in a collision.