Truck Suspension Part Glossary

5th wheel hitch: Sits in the bed of the truck and has a coupling to attach to a fifth wheel trailer for towing.

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A-arm: A linkage found in the front suspension formed in the shape of an "A" or "V". The A-arm is connected from the chassis to the wheel assembly by bushings, the two legs on the chassis side then the peak at the wheel assembly. Sometimes there's and upper A-arm and sometimes a lower A-arm there can even be both upper and lower A-arms in some cases.

Active suspensions: Automotive technology that senses changes in the road surface and automatically adapts the vehicles suspension to best suit driving conditions.

Air shock absorber: Helps to restrain the vehicles spring so that the car does not bounce up and down uncontrollably. Shock absorbers also help to control the vehicle from swaying as it drives.

Air springs: Bags that fill up with air in order to help support the vehicles suspension using pressure. On some vehicles air springs will replace conventional coil springs. Air springs purchased in the aftermarket can be installed in two different fashions; either inside the coil or between the axel and frame. These types of air springs are used to add additional support while towing or hauling.

Air suspension: A suspension system that uses air springs instead of conventional springs to maintain ride height and suspension characteristics.

All-wheel drive (AWD): All-Wheel Drive vehicles continuously send power to all 4 wheels to increase traction in all driving conditions. Unlike 4WD vehicles, AWD is active all the time and does not require a driver to engage the feature.

Anti-dive: An anti-dive will control the amount of front suspension deflection during braking. Load transfer is resisted through the suspension arms, sharing the load with the springs.

Anti-lift: Reduces the amount of pitch in the rear suspension while breaking.

Anti-roll bar: see Anti-sway bar

Anti-squat: Anti-squat reduces the amount of pitch in the rear suspension while accelerating.

Anti-sway bars: A round bar that can be located in the front or rear of the vehicle that reduces the roll angle and increases the balance of the vehicle under load.

Aspect ratio: The ratio of a tires section width (distance between the outside sidewalls when inflated) to its section height(distance between inside of the tire and outer tread when inflated).

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Ballast: Weight added to a vehicle to meet a minimum required weight. This is often used to adjust the vehicles balance.

Ball joint: Spherical bearings with a ball and socket design used to connect the control arms to the steering knuckles. This type of design resembles the human hip joint.

Bar rate (kbar): The Bar Rate is the torsional stiffness of the Sway Bar measured in lbs/in.

Bump: The movement of the wheel towards the chassis.

Bump steer: The tendency of the wheel to steer as it during upward motion. This is measured in degrees of steer per foot.

Bushings: A lining used to constrain, guide, or reduce friction when using a bolt. Bushings can be fixed or removable.

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Camber: The outward disposition of the front wheels leaving the bottom of the wheels slightly closer together than they are at the top of the wheel.

Caster Angle: The Caster Angle would be the angle between the upper and lower ball joints that the wheel revolves around.

Center of gravity: The location on the vehicle where all of the mass is located.

Chassis: The steel frame that holds the body of the vehicle. The chassis attaches to the axles and is supported by springs.

Coil over shock: I shock absorber assembled with a coil spring around it to achieve optimal dampening affects.

Coil springs: A spiral spring used in vehicle suspension to support weight and absorb shock. Heavy duty coils are used for plowing and many front-heavy load situations.

Compression Cycle: When the piston moves downward in the shock absorber, this will compress the hydraulic fluid inside the chamber below the piston.

Control arms: A triangle suspension member that attaches to the frame and pivots on a bushing.

Corner weights: The weight distribution across all four wheels of the vehicle. Corner weights will affect the handling of the vehicle.

CV joints: The constant velocity joint make it possible for a drive shaft to transmit power at varying angles with a steady rotational speed without increasing friction.

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Damper: A damper is another name for shock absorber. Dampers work by converting movement into heat resulting in hydraulic resistance.

Degrees per g: Degree of chassis roll per G of lateral acceleration.

Dependent system: A suspension system with a solid axle that connects the two wheels. This suspension system is kept in place by the springs and shocks.

Differential: A gear that controls the power to the wheels and allows them to rotate at varying speeds.

Dive: the front of a vehicle presses down on the springs when breaking.

Double-wishbone suspension: An independent suspension that uses two arms to locate the wheel. The arms connect to the shock absorber and coil spring to control vertical movement.

Down-force: the downwards motion of a vehicle caused by its aerodynamic characteristics. Down-force increases normal force creating more grip and allowing the vehicle to move faster around turns.

Droop: The vertical downward motion of the wheel from the chassis.

Drop links: Used to connect the sway bar to the suspension arms.

Dropped tube axles: Axle that lowers a vehicle made from steel tubing that offers optimal aerodynamics.

Dual/double a-arm (aa arm): Two arms that connect the chassis to the wheel. (see double wishbone suspension)

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Extension cycle: The extension cycle is when the piston moves towards the top of the pressure tube compressing the hydraulic fluid in the chamber above the piston.

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Four-wheel drive (4wd): A part-time system that will allow torque to be sent to all 4 tires to provide the maximum torque that will not cause a slip in the tire. 4WD vehicles will usually require the driver to engage the system manually and are only designed to be used in low-traction conditions.

Frame stiffness: Torsional stiffness of the chassis between the front and rear spring.

Friction circle: A graphic representation of traction capacity. This is used to identify the cause of traction loss.

Front steer: When the rack and tie rods are located in the front of the wheel.

Front Wheel Drive: When the engine powers the front wheels only.

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Gas-charged shocks: A shock that is powered by nitrogen gas that pressurizes the fluid in the shock to prevent foaming.

Grip: A tires Friction

Gross Vehicle Weight: The maximum operating weight and mass of a vehicle as specified by the manufacturer.

G's (a): Vehicles acceleration relative to the acceleration of Earth's gravity.

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Helper springs: A device used to increase level load capacity. This will allow a vehicle to carry a heavy load without compromising ride height or suspension.

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Independent system: A suspension system that supports the chassis on the wheels without solid axles. In an independent system the two wheels are not dependent on one another.

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Leaf springs: A spring that consists of a number of flexible metal slats that are clamped together and form an upward curve and provide suspension support.

Leveling kits: A kit that provides a certain lift to the front of a vehicle to make it level with the rear, reducing the factory rake.

Lift blocks: Blocks that are placed under the leaf springs in order to increase the height of a vehicle, often coming as part of a lift kit.

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Multi-link suspensions: This type of suspension system uses multiple lateral arms and one or more longitudinal arms rather than just an upper and lower control arm. This is usually found in independent suspension systems.

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Neutral steer: Ideal balance, neutral steer occurs when the front and rear tires give up traction at the same rate.

Normal force (n): Perpendicular force between a tire and the ground.

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Offset: Lateral distance between the center-line of the rim and where the hub mounts.

On Board Air compressor: Mounts to the inside of the vehicle to inflate the air springs from inside of the cab.

Outboard suspension: Suspension system that has the shock and spring mount directly in between the chassis and lower and upper arms.

Overhang: The distance between the furthest point of the vehicle in the front or rear and the center of the respective wheel. (Front overhang would be from the outside point in the front to the center of the front wheel)

Oversteer: When a vehicle tends to steer more than the driver anticipates.

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Pitch: The change in a vehicles angle respective to the ground.

Precession: A vehicle suspension moving forward during bump and rearward during droop.

Push: When the slip angle in the front tires is more than that of the rear tires during cornering, this will cause the front of the vehicle to slide outwards during turns.

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Rake: When the vehicle is lower on one end than the other.

Rack and pinion: A Steering system made up of a pinion at the end of a steering shaft that allows the wheel to control the direction of the tires.

Rear steer: When the rack and tire rods are located behind the wheel.

Rear Wheel Drive: When the engine only powers the rear wheels.

Rebound: Outward extension of springs and shocks providing roll control and control over the spring rate.

Recession: A vehicle suspension moving forward during droop and rearward during bump.

Ride height: The vertical distance between the road and the bottom of the vehicles frame.

Rocker: Suspension element that transfers wheel load onto the spring.

Rod end bearing: The bearing at the end of the suspension arm.

Roll axis: Longitudinal axis of a vehicle.

Roll center: Points in the front and rear of the vehicle where the sprung mass will rotate during turning, this is determined by where the suspension components are attached.

Roll couple distribution (rcd): Ration of weight transfer of front and rear wheels.

Roll flexibility: Degree of chassis roll per G of acceleration.

Roll steer: The direction that the rear axle causes the vehicle to move during travel.

Roll stiffness (rs): The resistance of a vehicles suspension against the rolling of the vehicles weight.

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Scrub radius: Distance between center of the tire where the steering axis intersects the ground and center of the ball joints.

Section height: Distance from wheel rim to tread surface (unloaded).

Section width: Maximum sideways dimension of tire (unloaded).

Shock absorbers: See damper.

Short-long-arm (SLA): When a suspension system has a short upper arm and a long lower arm.

Side view instant center (SVIC): The point that the wheel rotates instantaneously from the side view.

Single wheel bump rate (SWBR): The Vertical travel stiffness of a wheel when only one of the four wheels hits a bump.

Solid axle: An axle that runs all the way across from left to right connecting the wheels.

Spool: Where the le left and right wheels on the rear axle rotate at the same speed.

Spring rate (ksp): The stiffness of a spring that is measured in pounds per inch.

Sprung mass (m): The weight of the vehicle, not including suspension components, that is supported by the springs.

Squat: When the rear of a vehicle sags down below natural ride height during acceleration.

Static weight distribution: Down force of the front and rear tires when the vehicle is still.

Steering arm: An arm connected to the steering knuckles that cause the wheels to pivot.

Steering rack: Where the pinion connects to allow the control of wheel movement by the steering wheel.

Steering stabilizers: Similar to a shock but is placed across the axle and attached to the steering link to absorb road shock.

Strut: Found on front wheel drive vehicles, struts reduce road shock in the front of the vehicle and eliminate the need for an upper suspension arm. On many pickups, parts like the silverado strut spacer can be used to level the vehicle.

Suspension air bags: see air springs

Suspension lift kits: When the vehicle is lifted by the suspension creating higher ground clearance, greater travel. A suspension lift kit will also allow use of lager tires.

Suspension system: Supports the weight of the vehicle.

Sway bar: See anti-sway bar

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Tie rod: Part of the steering mechanism, it operates in both tension and compression.

Toe-in/toe-out: How much a front wheel is pointed either in or out.

Torsion bars: Long metal bar attached to the chassis that supports load by twisting.

Traction bars: Used to control axle wrap (unwanted rotating of the drive axle housing that causes wheel hop). Traction bars help to prevent the springs from bending and rotating the axle.

Turnoverball gooseneck hitch: An in-bed hitch that allows for the removal of the hitch ball and ability to turn the ball over and place it down into the bed for storage. This leaves a level bed for loading when the hitch is not in use.

Twin-tube design: A common design of shock using a two tube system, an outer tube and an inner tube. Valves between the outer and inner tubes restrict oil flow to control wheel motion.

Two Wheel Drive: When energy is only transferred to 2 of the vehicles wheels.

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Understeer: When a car steers less than the amount that the driver is directing it to.

Unsprung mass (m): The weight of the suspension and related components

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Viscous coupled differential: Device that uses fluid between two plates to keep wheel spin limited.

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