The act of steering a vehicle may seem relatively self-explanatory, but the mechanics that translate a driver turning the steering wheel to the redirection of the wheels are actually pretty complex. For instance, when turning a corner, each front wheel needs to make a different arc for the car to turn smoothly. The inside wheel is following a shorter path than the wheel on the outside of the turn, and will need to turn further to successfully make it around the corner. This is controlled by the steering gear, of which there are two types - rack-and-pinion and recirculating-ball steering.
Rack-and-pinion steering is growing more common in SUVs and trucks, but is still predominantly used in cars. The pinion gear is attached to the base of the steering column, and when the driver turns the wheel, the pinion will spin accordingly. Its teeth move the rack, which will adjust the tie-rods so the wheels will turn properly in accordance with the driver's command. The rack-and-pinion steering system provides a reduced gear ratio that makes it easier to use the steering wheel.
Some vehicles are equipped with variable-ratio steering that has different teeth on the inside and outside of the rack to provide more accurate turning responses when starting a turn and when nearing the wheel's turning limits.
The recirculating-ball set-up can be found on many new SUVs and trucks. This system utilizes worm gears that serve to reduce the gear ratio. The worm gear is housed inside a block with a threaded hole. When the driver turns the steering wheel, the shaft spins the gear inside the block. The gear is also loaded with ball bearings to reduce friction and wear, which is where the system gets its name. Without the ball bearings, the steering wheel would feel loose when changing its direction.
Power steering is used to facilitate the turning process, and has been around since the early 20th century. Without power steering, it requires the driver to exert a large amount of force to manually turn the wheels. A power steering system typically uses hydraulic pressure to help turn the wheel, which is especially necessary when a vehicle is stopped or moving slowly.