ASE H5 Suspension & Steering (Transit Bus) key terms

A linkage layout that makes the inner front wheel turn a sharper angle than the outer wheel during a turn, so both wheels roll on circles sharing a common center and tire scrub is minimized.

The difference in steer angle between the inner and outer front wheels when the steering wheel is held at a set angle, used to check that the steering arms produce correct Ackermann geometry and that linkage is not bent.

The forward or rearward tilt of the steering axis from vertical as viewed from the side of the vehicle; positive caster leans the top of the axis rearward and adds straight-line stability and steering return.

The inward or outward tilt of the top of the wheel from vertical as viewed from the front; negative camber tilts the top inward and is used to offset deflection under load.

The inward tilt of the steering axis (kingpin or strut axis) from vertical as viewed from the front, which works with camber to place the tire contact patch and affects steering feel and wheel return.

The total angle formed by adding camber to steering axis inclination; it is built into the knuckle and strut and cannot be adjusted, so an out-of-spec reading points to a bent component.

The direction the rear axle points relative to the vehicle centerline, calculated from rear toe readings; a nonzero thrust angle causes the steering wheel to be off-center and the vehicle to dog-track.

An alignment procedure that measures and adjusts both front and rear wheel angles so all wheels are referenced to the vehicle centerline and the thrust line, rather than setting front angles alone.

The amount the front edges of a pair of tires are closer together (toe-in) or farther apart (toe-out) than the rear edges, adjusted at the tie rod sleeves and used to control tire scrub and straight-line tracking.

The adjustable link connecting the steering gear or rack to the steering arm on the knuckle; its threaded sleeve sets front toe and it transmits steering force to the wheel.

The ball-and-socket joint at the outer end of a tie rod that attaches to the steering knuckle arm, allowing the wheel to steer and to move with suspension travel without binding.

A link that carries steering motion from the steering gear pitman arm to the steering knuckle or center link on a conventional (non-rack) steering system.

A cross link in a parallelogram steering linkage that ties the left and right tie rods and the idler arm together and moves side to side as the steering wheel is turned.

The arm splined to the steering gear output shaft that converts the gear's rotation into lateral movement of the steering linkage.

A pivoting support on the passenger side that holds one end of the center link at the correct height and lets the linkage swing while keeping the geometry stable.

A steering gear in which a worm shaft and ball nut, filled with recirculating steel balls, convert steering wheel rotation into pitman arm movement with low friction and high mechanical advantage.

A steering system in which a pinion on the steering column drives a toothed rack that moves side to side, with tie rods attached at each end of the rack.

An engine- or electric-driven hydraulic pump that supplies pressurized fluid to the steering gear or rack, giving assist proportional to steering effort and input torque.

A valve in or on the power steering pump that limits fluid volume delivered to the steering gear as engine speed rises, preventing excessive assist and fluid heating.

A spring-loaded valve that opens to bypass pump flow when system pressure reaches its limit, protecting hoses, seals, and the gear from overpressure at full lock.

The assembly of shaft, tube, bearings, and mounts that carries steering wheel input to the gear, and that collapses or breaks away in a collision to limit driver injury.

A steering column designed with sliding sections, mesh sections, or breakaway brackets so it shortens or yields during a frontal impact instead of driving the shaft into the driver.

A flat coiled ribbon conductor inside the steering wheel hub that maintains electrical contact for horn, airbag, and wheel-mounted controls while the wheel turns through its full range.

A joint with two yokes and a cross that lets the steering shaft transmit torque through an angle between the column and the gear or between column sections.

A lubricated socket-and-stud joint that connects the control arm to the steering knuckle, allowing the knuckle to pivot for steering and to swing with suspension travel.

A pivoting suspension link, upper or lower, that locates the knuckle or axle and carries spring and load forces between the frame and the wheel.

A hardened vertical pin that joins a solid axle to the steering knuckle on heavy-duty front axles, allowing the knuckle to pivot for steering around a fixed inclination.

The forged part that carries the wheel hub and spindle and pivots on the ball joints or kingpin to steer, and to which the steering arm and tie rod attach.

A helical spring that supports vehicle weight and absorbs road input, seated between the frame or strut tower and the control arm or axle.

A hydraulic damper that converts suspension motion into heat to control spring oscillation, keeping the tire in contact with the road over bumps.

A structural suspension member that combines a damper with a spring seat and often serves as the upper locating member for the knuckle, as in a MacPherson design.

A stack of curved steel leaves clamped together that supports axle load and locates the axle fore-and-aft; used widely on rear suspensions of heavy vehicles.

A rubber-and-fabric bellows filled with compressed air that supports load and can be inflated or deflated to hold ride height as passenger or cargo weight changes.

A valve linked between the axle and frame that senses ride height and adds or exhausts air from the air springs to maintain the designed suspension height under varying loads.

A pivoting link that attaches one end of a leaf spring to the frame, allowing the spring to lengthen as it flattens under load without binding.

A U-shaped clamp that secures a leaf spring pack or axle seat to the axle housing, maintaining alignment and transmitting torque and braking forces.

A replaceable sleeve, usually rubber or polyurethane, pressed into a suspension or steering pivot to isolate vibration and allow controlled movement without metal-to-metal contact.

The measured distance between a specified frame or body point and the ground or axle, used to confirm springs are not sagged and to set alignment reference points.

The variation in a wheel or tire's radius as it rotates, measured with a dial indicator; excessive runout causes vibration and uneven tire wear.

Side-to-side wobble of a wheel or tire measured at the sidewall or bead area as the assembly rotates; too much can mimic balance or alignment problems.

The distribution of mass around a wheel and tire so it rotates without vibration; corrected with static and dynamic balancing using clip-on or adhesive weights.

The consistency of a tire's stiffness and roundness around its circumference; variations in force cause vibration and irregular wear even when balance is correct.

The manufacturer-specified tightening value, applied with a calibrated wrench, for fasteners such as lug nuts and suspension bolts to prevent loosening or thread damage.

The toe angle of the rear wheels relative to the vehicle centerline; it is a primary input to thrust angle and affects tire wear and handling stability.

The size of the circle a vehicle traces at full steering lock, determined by steering linkage travel, wheelbase, and body clearance; uneven side-to-side radius suggests a bent or misadjusted linkage.

The reduction mechanism, either recirculating ball or rack and pinion, that converts steering wheel rotation into linear movement of the steering linkage with mechanical advantage.