The idea
Beginner explanation — switch to Technical for the engineering detail.
The steering wheel turns a shaft that ends in a small gear called the pinion. The pinion's teeth mesh with a toothed bar called the rack, which runs across the car. As the pinion turns, the rack slides left or right, and track rods at each end push or pull arms on the front wheel hubs, swivelling the wheels.
It takes several turns of the steering wheel to swing the front wheels from full left to full right. That gearing — the steering ratio — makes steering precise and lighter to operate. Most cars also have power assistance: an electric motor (or, in older cars, a hydraulic pump) adds force so parking is easy, while the system gives less help at speed so the steering feels steady.
The geometry matters too. In a turn the inside wheel follows a tighter circle than the outside wheel, so the linkages are arranged to turn it slightly more. And the wheel pivots are tilted so the car naturally wants to drive straight, which is why the steering wheel returns to centre after a corner.
What you will learn
- Describe how a rack-and-pinion mechanism converts rotation into sideways motion
- Calculate road-wheel angle from steering ratio
- Explain Ackermann geometry and why the inner wheel steers more
- Compare hydraulic and electric power steering and explain self-centring from caster
How it flows
Read the diagram as text
- Steering wheel → Torque sensor & motor
- Torque sensor & motor → Pinion & rack
- Pinion & rack → Track rods
- Track rods → Steering knuckles
- Steering knuckles → Tyres
- Tyres → Steering wheel (self-aligning feel)
- Steering wheel: Driver torque
- Torque sensor & motor: Speed-mapped assist
- Pinion & rack: Rotation → translation
- Track rods: Set toe
- Steering knuckles: Ackermann arms
- Tyres: Slip angle → cornering force
Step by step
Read each step in order.
Step 1: Pinion drives the rack
Turning the wheel spins a small gear that slides a toothed bar left or right.
Step 2: Track rods swivel the hubs
Rods at each end of the rack push and pull arms on the hubs so the wheels pivot.
Step 3: Gearing makes it precise
Several turns of the steering wheel give only a modest turn of the road wheels.
Step 4: Inner wheel turns more
The inside wheel follows a tighter circle, so the linkage steers it at a sharper angle.
Step 5: Assistance and self-centring
A motor adds force when needed, and tilted pivots make the wheel return to centre.
Go deeper
Optional. Open a panel for the engineering detail — or switch to Technical above.
The engineering explanation3
Rack-and-pinion steering converts pinion rotation to rack displacement x = r_pinion × θ. The overall steering ratio — steering-wheel angle divided by mean road-wheel angle — is typically about 12:1 to 18:1 for cars, giving roughly 2.5 to 3.5 turns lock to lock. Variable-ratio racks cut teeth with changing pitch so the ratio is slower near centre (stable on the motorway) and quicker towards lock (easier parking). Recirculating-ball steering boxes, with balls running between a worm and a nut to reduce friction, remain common on heavy vehicles with beam axles.
Ackermann geometry angles the steering arms so that, in a slow turn, lines through both front wheel axes meet on the extension of the rear axle line; the inner wheel therefore steers more than the outer and neither tyre scrubs. At higher speeds tyres run with slip angles, so production cars often use partial Ackermann. Wheel alignment adds further terms: toe (wheels pointing slightly in or out) affects straight-line stability and tyre wear; caster tilts the steering axis rearward at the top, putting the tyre's contact point behind the axis (mechanical trail) so lateral force creates a self-aligning moment; kingpin inclination and scrub radius shape steering feel and how braking forces feed back.
Hydraulic power steering uses an engine-driven pump and a rotary valve on a torsion bar: driver torque twists the bar, opening ports that direct fluid to one side of a piston on the rack. Electric power steering (EPS) measures driver torque with a torque sensor and drives an electric motor on the column, pinion or rack, with assistance mapped against vehicle speed. Because it draws power only when steering and can be commanded by software, EPS saves fuel and enables lane-keeping assistance and automated parking; steer-by-wire systems remove the mechanical column entirely, with redundant actuators.
Key concepts4
- Steering ratio
- Steering-wheel angle divided by the resulting road-wheel angle.
i_s = θ_wheel / δ_road- Ackermann geometry
- Linkage layout that makes the inner wheel steer more than the outer so both roll about a common centre.
- Caster and trail
- Rearward tilt of the steering axis places the contact patch behind it, producing self-centring.
- Toe
- The angle of the wheels relative to the car's centreline viewed from above; small amounts strongly affect stability and tyre wear.
Common misconceptions3
MythLight steering means the car has less grip.
RealityAssistance level is a tuning choice. Steering effort says little about available grip, although a sudden lightening at speed can indicate front tyres beginning to slide or aquaplane.
MythWheel alignment only matters after an accident.
RealityKerb strikes and worn joints shift alignment; even small toe errors noticeably shorten tyre life and can make the car pull.
MythBoth front wheels always point in exactly the same direction.
RealityIn a turn the inner wheel deliberately points more sharply than the outer, thanks to Ackermann geometry.
In the real world3
- Releasing the steering wheel gently after a slow corner and watching it unwind shows caster's self-centring effect.
- Tyres worn on one edge often indicate incorrect toe or camber rather than a tyre fault.
- A car that pulls to one side on a level road may have uneven tyre pressures, an alignment error or a sticking brake.
Common questions
Short answers to the questions people most often ask about this topic.
How does rack-and-pinion steering work?
The steering column turns a small pinion gear meshed with a toothed bar, the rack. As the pinion turns, the rack slides sideways and pushes or pulls tie rods connected to each front wheel's steering arm, swivelling the wheels.
What is Ackermann steering geometry?
In a turn the inner front wheel follows a tighter circle than the outer one, so it must turn through a larger angle. Ackermann geometry angles the steering arms so the wheels turn by different amounts and roll around a common centre without scrubbing.
How does power steering work?
Power steering adds force to what the driver applies. Hydraulic systems use a pump and a valve that directs pressurised fluid to one side of a piston on the rack; electric systems use a motor on the column or rack, controlled by a torque sensor.
Check your understanding
3 questions. Your best score is saved in this browser.
0 of 3 answered
Question 1 of 3
A car has a 15:1 steering ratio. You turn the steering wheel 90°. Roughly how far do the road wheels turn?
The story behind it
Who worked this out, and what they were up against. Optional.
1816
Georg Lankensperger
Carriage builder, Munich
Worked out how the front wheels should turn, and lost the naming rights.
Lankensperger invented the geometry in Munich in 1816. The aim is for each wheel's axle to lie along a radius of circles sharing a common centre, so the tyres do not slip sideways in a turn, which means the inner wheel must turn through a greater angle than the outer. His English agent, Rudolph Ackermann (1764–1834), patented it in England in 1818 for horse-drawn carriages, and the geometry carries Ackermann's name today.
Worth knowing: Erasmus Darwin may have a prior claim, dating from 1758. Modern cars do not use pure Ackermann steering, partly because it ignores dynamic and compliance effects, though the principle still holds for low-speed manoeuvres.
Sources
Retold in our own words from the sources above.
1926
Francis W. Davis
Engineer at Pierce-Arrow
Built the first workable power steering, and General Motors found it too costly.
Francis W. Davis, an engineer at Pierce-Arrow, is credited with developing the first workable power steering system in 1926. Later, at General Motors, he refined it, but the company judged it too costly to produce. Chrysler's 1951 Imperial, sold with the Hydraguide system, was the first commercially available passenger car with power steering, and the heavy vehicles of World War II gave development another push.
Worth knowing: Robert E. Twyford's 1900 patent included a mechanical power steering mechanism, and the source also mentions an 1876 installation by someone named Fitts with few details known.
Sources
Retold in our own words from the sources above.
Almost there
- Overview — Read the introduction to the end.
- See it work — 5 steps left to read
- Go deeper (optional) — Optional: open a deeper panel or switch to Technical.
- Check — Answer the quiz questions.
- Story (optional) — Optional: who worked this out?
Progress is stored only in this browser — there is no account.
Earlier in this route you skipped Brake Hydraulics, Disc Brakes, Anti-lock Braking (ABS).
Sources & attribution
Further reading
- How the steering system worksHow a Car Works · consulted 2026-10-21(external site, opens in a new tab)
Further reading on an external site. Linked only; AutoVerse lesson text is written independently.
- Licence
- AutoVerse original content
This lesson is original AutoVerse writing. The links above are suggestions for further reading, not the source of this text.