ASE A4 key terms

A steering system in which a pinion gear on the steering shaft turns a toothed rack, and the rack's side-to-side movement pushes the tie rods to pivot the front wheels.

A steering gear that uses a worm shaft and a ball nut with recirculating steel balls to convert steering wheel rotation into movement of a Pitman arm, common on older trucks and large vehicles.

A hydraulic valve inside a power steering gear or rack that senses twist between the input shaft and the gear and directs pressurized fluid to the correct side to assist steering effort.

A power steering system that uses an electric motor, controlled by a module reading steering torque and vehicle speed sensors, to provide assist instead of an engine-driven hydraulic pump.

The rod that threads into the end of the steering rack and connects to the outer tie rod; its threaded adjustment sets front toe on many vehicles.

The ball-and-socket joint at the outer end of a tie rod that attaches to the steering knuckle, allowing the wheel to pivot while transmitting steering motion.

A lever splined to the steering gear output shaft that converts the gear's rotary output into the side-to-side motion that drives the steering linkage.

The small amount of clearance between the meshing parts of the steering gear; too much produces steering wheel free play, while too little causes binding and poor return.

A suspension design in which a single unit combines the shock absorber, coil spring and upper mount, and also serves as the upper locating member for the wheel.

A suspension layout using upper and lower control arms of unequal length so wheel camber changes are controlled as the suspension moves through jounce and rebound.

A helical steel spring that supports vehicle weight, compresses and extends as the suspension travels over bumps, and also establishes ride height.

A stack of curved steel leaves that supports the axle and locates it front to back; common on rear suspensions of trucks and older vehicles.

A hydraulic damper that converts suspension movement into heat to control spring oscillation, keeping the tire pressed against the road after a bump.

The bearing in the top mount of a MacPherson strut that lets the strut and spring rotate with the steering knuckle when the wheels are turned.

A torsion spring connected to both sides of the suspension through links; when the body rolls, the bar twists and resists that roll to improve handling.

A pivoting socket joint that connects a control arm to the steering knuckle, allowing suspension and steering movement through their range without binding.

An elastomeric or spherical pivot at the control arm's frame attachment that allows suspension movement while isolating road noise and vibration from the body.

The angle of the wheel measured from vertical when viewed from the front; negative camber tips the top of the tire inward, positive camber tips it outward.

The forward or rearward tilt of the steering axis viewed from the side; positive caster leans the axis rearward and improves straight-line stability and steering return.

The difference in distance between the front and rear of the two tires when viewed from above; toe-in points the fronts toward each other, toe-out points them apart.

The direction the rear axle points relative to the vehicle centerline, calculated from rear toe; when it is not zero the steering wheel will be off center.

The inward tilt of the steering axis from vertical as seen from the front; it is built into the knuckle and strut and is not adjustable.

The sum of camber and steering axis inclination for a wheel; comparing it side to side helps identify a bent knuckle, strut or spindle.

The distance at the road surface between the steering axis centerline and the center of the tire contact patch; it affects steering feel and road kickback.

The change in toe angle of the front wheels as the steering wheel is turned, caused by the steering arms' angle and needed for the inner wheel to follow a tighter arc.

The checks performed before measuring alignment, including tire pressures, ride height, tire condition, and play in ball joints, tie rods and wheel bearings.

The tire's sidewall height expressed as a percentage of its section width; a 60-series tire's sidewall is 60 percent as tall as the tire is wide.

A number molded on the tire sidewall that corresponds to the maximum load the tire can carry at its rated inflation pressure.

A letter molded on the tire sidewall indicating the maximum sustained speed the tire is designed to withstand when properly inflated and loaded.

The distance between the wheel's mounting face and its centerline; positive offset moves the mounting face outward, negative offset moves it inward.

The diameter of the circle passing through the centers of the wheel's lug holes, usually written with the stud count, such as 5 x 114.3.

A balance measurement that also detects stiffness differences around the tire by pressing a loaded roller against it, revealing vibration causes that ordinary balancing misses.

A system that monitors tire pressure with wheel-mounted sensors and illuminates a warning light when pressure falls below a specified threshold.

The label on the driver's door jamb listing the manufacturer's recommended cold tire pressures, tire size and load limits for the original equipment.

A condition where the vehicle continues to pull in the direction the steering wheel was last turned after the driver releases it, usually from binding strut bearings or steering linkage.

A pull to one side during acceleration in front-wheel-drive vehicles caused by unequal driveshaft angles or lengths, which changes the steering effect of engine torque.

A change in toe angle as the suspension moves up and down, caused by incorrect tie rod height or geometry, making the vehicle dart when it hits bumps.

A rapid side-to-side oscillation of the front wheels and steering wheel, typically triggered by tire or wheel imbalance, runout, or worn steering and suspension parts.

A sensor on the steering column that reports steering wheel position to the stability control and electric power steering systems; it usually needs recalibration after alignment or column repair.