WinAlign® HD Wheel Alignment Education Guide for Heavy-Duty Trucks

Ackerman Principle: An alignment principle based on vehicle tread width and wheelbase upon which turning angle is computed.

Ackerman Arm: A steering component, which provides interconnection between the outer tie rod and spindle.

Alignment: The process of measuring and adjusting the position of all wheels attached to a common chassis.

Angle: Two intersecting lines that are not parallel.

Arc: Any part of a circle or a curved line.

Axial Play: Vertical movement of the wheel and tire assembly when inspecting a kingpin.

Balance: This term is used to describe having equal weight distribution about the circumference of a wheel and tire assembly.

Bead: A wire steel coil forming an anchor for individual plies and rim attachment of a tire.

Bellows: A rubber type seal, which is folded to allow for a telescopic action. Normally referred to as a bellows boot.

Bias Belted: A bias ply tire that has reinforcing strips or belts under the tread section.

Bias Ply: A tire constructed of alternate plies, which intersect the tire centerline at approximately 35 degrees.

Body Roll: The leaning of the vehicle body while cornering.

Braking Control: Vehicle stability related to the reaction under all stopping conditions.

Bushing: A component made of metal or rubber-type material, used to isolate interconnected moving parts.

Cam Bolt: A bolt and eccentric assembly which, when rotated, will force components to change position.

Camber: The inward or outward tilt of the wheel.

Camber Roll: A change in camber brought about by suspension changes while cornering.

Caster: The forward or rearward tilt of the steering axis.

Center Bolt: A bolt that provides centering and attachment of an axle and spring assembly.

Centerline Steering: A centered steering wheel while the vehicle is traveling a straight ahead course.

Chassis: All major assemblies on a vehicle including suspension, steering, drivetrain, and frame. Everything, except the body.

Circumference: The total distance around a circle.

Concentric: Two or more components sharing a common center.

Conicity: A tire irregularity, which causes the tire to take the shape of a cone when inflated and loaded. This may generate a lateral force.

Contact Area: The total amount of tread surface that contacts the road.

Cornering: The ease at which a vehicle travels a curved path.

Cross Tube Assembly: Two tie rods and a tube, which transfers the turning effort to the opposite side of the vehicle.

Curb Weight: The overall weight of a vehicle, less passengers, luggage, or load.

Degree: A unit of measurement to describe an angle.

Dial Indicator: An instrument used to measure and display linear displacement. Measurement is displayed on a dial face and the scale is commonly graduated in thousandths.

Directional Stability: The tendency for a vehicle to maintain a directed path.

Drag Link: A tube or rod used for interconnection between Pitman Arm and tie-rod assemblies.

Dynamic Balance: This normally refers to the balance condition of a wheel and tire assembly in motion.

Foot Pound: A unit of measurement used to describe torque force.

Frame Angle: The angle formed by a horizontal line and a line drawn parallel to the frame.

Geometric Centerline: A line drawn between the midpoint of the front axle and the midpoint of the rear axle.

Horizontal: Parallel or level with the plane of the horizon.

Hub: The assembly that houses the bearings about which the wheel and tire assembly rotates.

Hydraulic Pump: A power driven device generating constant volume and pressure. Included Angle: The sum of the angles, camber and SAI.

Independent Suspension: A suspension system that provides an isolated mounting for each wheel to the chassis.

Individual Toe: The angle formed by a horizontal line drawn through the plane of one wheel versus a centerline.

Intersect: The crossing point of two lines.

Jounce Travel: A suspension moving up through its travel.

Kinetic Balance: The balance condition of a rotating wheel related to force generated in a vertical plane.

King Pin: A pin used to attach a spindle to an axle.

Lateral Run-out: Side-to-side movement with a rotating wheel or tire.

Lead: A slight tendency for a vehicle to move away from its directed course.

Linkage: A series of rods or levers used to transmit motion or force.

Load Range: A system used to describe the service or weight limitations of a tire.

Memory Steer: A condition where the wheels, rather than returning to straight ahead, tend to remember and seek a previous position.

Millimeter: A unit of linear measurement. One millimeter is equivalent to 0.039 inches.

Minute: A unit of measurement used to describe an angle. One minute is equivalent to 1/60 of one degree.

Offset: The lateral displacement of a wheel or axle in respect to a centerline.

Oscillate: A back and forth motion at a specific frequency.

Out-of-Round: A wheel and tire irregularity in which one or both are not concentric with its axis of rotation.

Overinflation: Inflation pressure beyond that which is recommended.

Oversteer: A characteristic in which a vehicle has a tendency to turn sharper than the driver intends.

Parallelogram Steering Linkage: A steering linkage design where if all pivot points were connected by lines, these lines would be parallel.

Perpendicular: Being at right angles.

Pitman Arm: A steering component that provides interconnection between the steering gear sector shaft and the steering linkage.

Ply Rating: A method of rating tire strength. Not necessarily indicative of the actual number of plies used.

Power Steering: A steering system that incorporates hydraulics to assist in the steering of the wheels.

Pre-load: A predetermined amount of load or force applied during assembly to prevent unwanted play during actual operation.

Pull: The tendency for a vehicle to steer away from its directed course.

Radial Play: Any lateral movement of the wheel and tire assembly when inspecting a ball-joint or kingpin.

Radial Ply Tire: A tire construction type with alternating plies 90 degrees to the tire bead.

Radius: The distance from the center to the outer edge of a circle.

Rear Axle Departure Offset: The amount in inches from the midpoint of the steer axle (or kingpin on a trailer), where the projected thrustline intersects.

Rebound: A suspension moving down through its travel.

Recirculating Ball Steering Gear: A steering gear design that is made up of a worm shaft, ball nut, and two recirculating ball circuits.

Returnability: The tendency of the front wheels to return to a straight ahead position.

Road Crown: The slope of a road from its center.

Road Feel: Necessary feedback transmitted from the road surface up to the steering wheel.

Road Isolation: The ability of a vehicle to better separate road irregularities from the driver and passengers.

Road Shock: An excessive amount of force transmitted from the road surface up to the steering wheel.

Scrub Radius: The radius formed at the road surface between the wheel centerline and steering axis.

Semi-Integral Power Assist: A power assist system using a hydraulic pump and a power cylinder in conjunction with the steering gear.

Setback: The angle formed between a centerline and a line perpendicular to the front axle.

Shim: Thin material of fiber or metallic makeup used to take up clearance between two parts.

Shimmy: A violent shake or oscillation of the front wheels transmitted up to the steering wheel.

Shock Absorber: A suspension component used to dampen spring oscillation.

Solid Axle Suspension: A suspension system consisting of one steel or aluminum I-beam extended the width of the vehicle.

Short Long Arm (SLA): An independent suspension design incorporating unequal length control arms.

Spindle: A component on which a wheel and tire assembly rotates.

Stability: The tendency of a vehicle to maintain a directed course.

Stabilizer: A steel bar used to minimize body roll.

Steering Axis Inclination: The angle formed by an imaginary line drawn through the steering axis versus vertical.

Steering Gear: A mechanical device used to convert the rotary motion at the steering wheel to a lateral motion.

Steering Shaft: A tube or rod, which interconnects the steering wheel to a lateral motion.

Strut: Any support used between two parts.

Suspension: An assembly used to support weight, absorb and dampen shock, help maintain tire contact and proper wheel to chassis relationship.

Suspension Height: The specified distance between one or more points on a vehicle to the road surface.

Tandem Lateral Offset: When the geometric centerline does not cross the midpoint of all axles.

Tandem Scrub Angle: The angle formed by the intersection of horizontal lines drawn through each rear axle when total toe and the offset is zero.

Thrust Angle: The angle formed by thrustline and geometric centerline.

Thrustline: A bisector of rear total toe.

Tie Rod Assembly: The outer most assemblies on a parallelogram steering linkage. These assemblies are attached to the drag link and Ackerman Arms.

Tie Rod End: The ball and socket assembly of a tie rod.

Tie Rod Sleeve: A threaded tube that provides connection and adjustment of a tie rod assembly.

Tire Force Variation: A tire irregularity, in which there is a difference in radial stiffness about the circumference of the tire.

Toe: The comparison of a horizontal line drawn through both wheels of the same axle.

Turning Angle: The difference in the turning angle of the front wheels in a turn.

Torsion Bar: A spring steel bar used in place of a coil spring.

Tracking: The interrelated paths taken by the front and rear wheels.

Treadwidth: The dimension as measured between the centerlines of the wheels on the same axle.

Treadwear Indicators: Ridges molded between the ribs of the tread that visibly indicate a worn tire.

Under Inflation: Air pressure below that which is specified.

Understeer: A characteristic in which a vehicle has a tendency to turn less than the driver intends.

Vertical: Being exactly upright or plumb.

Vibration: To constantly oscillate at a specific frequency.

Waddle: The lateral movement of a vehicle, usually caused by some type of tire or wheel imperfection.

Wander: The tendency of a vehicle to drift to either side of its directed course.

Wheelbase: The dimension as measured between the center of the front and rear axles.