Editing Steering (section)

===Rack and pinion, recirculating ball, worm and sector===
[[Image:WrightspeedStearingRack4888.JPG|thumb|250px|right|Rack and pinion unit mounted in the cockpit of an [[Ariel Atom]] sports car chassis, atypical of contemporary production automobiles]]
[[Image:Scatola di sterzo.jpg|thumb|Non-assisted steering box of a motor vehicle]]

Many modern cars have a steering mechanism called a [[rack and pinion]]. The steering wheel turns a pinion gear, which moves a rack back and forth to steer the wheels. This mechanism converts the circular motion of the steering wheel to [[linear motion]], which is applied to the wheels of the car via [[tie rod]]s and a [[steering knuckle]].

Rack and pinion steering has several advantages, such as a direct steering "feel". This means that the driver can feel the road better and have more precise control over the car's movement.

[[BMW]] was one of the first manufacturers to adopt rack and pinion steering systems in the 1930s, with many other European manufacturers following suit. Auto manufacturers in the [[United States]] began to use rack and pinion steering with the 1974 [[Ford Pinto]].<ref>{{cite web |url=http://www.hemmings.com/hmn/stories/2010/07/01/hmn_feature20.html |title=Rack and Pinion Steering &#124; Hemmings Motor News |access-date=2015-07-24 |url-status=live |archive-url=https://web.archive.org/web/20150710194851/http://www.hemmings.com/hmn/stories/2010/07/01/hmn_feature20.html |archive-date=2015-07-10 }}</ref>

Older designs use two main principles: the worm and sector design and the screw and nut. Both types were enhanced by reducing the friction; for screw and nut it is the [[recirculating ball]] mechanism, which is still found on trucks and utility vehicles. The steering column turns a large screw, which meshes with the nut by recirculating balls. The nut moves a sector of a gear, causing it to rotate about its axis as the screw is turned; an arm attached to the axis of the sector moves the [[pitman arm]], which is connected to the steering linkage and thus steers the wheels. The recirculating ball version of this apparatus reduces the considerable friction by placing large ball bearings between the screw and the nut. At either end of the apparatus, the balls exit from between the two pieces into a channel internal to the box, which connects them with the other end of the apparatus. Thus, they are "recirculated".

The recirculating ball mechanism gives a driver a greater mechanical advantage, resulting in its use on larger, heavier vehicles, while the rack and pinion would originally be limited to smaller and lighter ones; due to the almost universal adoption of [[power steering]], however, this is no longer considered an important advantage, leading to the increasing use of rack and pinion mechanisms on newer cars. The recirculating ball design also has a perceptible lash, or "dead spot" on center, where a minute turn of the steering wheel in either direction does not move the steering apparatus; this is easily adjustable via a screw on the end of the steering box to account for wear, but it cannot be eliminated because it will produce excessive internal forces at other positions and the mechanism will wear very rapidly. This design is still in use in trucks and other large vehicles, where rapidity of steering and direct feel are less important than robustness, maintainability, and mechanical advantage.

The worm and sector was an older design, used for example in [[Willys MB|Willys]] and Chrysler vehicles, and the Ford Falcon (1960s). To reduce friction, the sector is replaced by a roller or rotating pins on the rocker shaft arm.

Generally, older vehicles use the recirculating ball mechanism, and only newer vehicles use rack-and-pinion steering. This division is not very strict, however, and rack-and-pinion steering systems can be found on British sports cars of the mid-1950s, and some German carmakers did not give up recirculating ball technology until the early 1990s.

Other systems for steering exist, but are uncommon on road vehicles. Children's toys and [[go-kart]]s often use a very direct [[Linkage (mechanical)|linkage]] in the form of a [[bellcrank]] (also commonly known as a pitman arm) attached directly between the steering column and the steering arms, and the use of cable-operated steering linkages (e.g. the capstan and bowstring mechanism) is also found on some home-built vehicles such as [[soapbox car]]s and [[recumbent tricycle]]s.