Glossary of Suspensions Terminology

Suspension related term

Meaning

A-arm,

(control arm), (wishbone)

A suspension linkage formed in the shape of an A or V found commonly on the front suspension. The sides of the two legs of the A-arm are connected to the chassis by rubber bushings and the peak of the A-arm is attached to the wheel assembly.

Acceleration

The rate of change of velocity or speed. It is measured in velocity per time (e.g. meters per second per second or m/s²). It may be positive or negative (deceleration) depending upon whether the object is speeding up or slowing down. According to Newton's second law of motion, acceleration is equal to the force, divided by mass (A=F/M).

Ackermann steering geometry

With perfect Ackermann, at any angle of steering, the center point of all of the circles traced by all wheels will lie at a common point.

Active suspension

Active suspensions uses some type of actuator to literally raise and lower the chassis independently at each wheel. The up and down motion of the wheels is actuated by electronically controlled valves.

Adaptive suspension

Adaptive suspensions only vary shock absorber firmness to match changing road or dynamic conditions.

Adhesion

The ability of a tire to grip the surface of the road.

Adjustable shock absorber

Adjustable rate shock absorbers provide a means of changing their rate of dampening of the spring oscillations, to suit road conditions. Electronic controls let the changes occur either automatically, or as the driver prefers.

Air (Pneumatic) spring

Air-filled rubber or elastomer bags that are pressurized to provide support to the suspension. Air springs are used in place of conventional coil springs on some vehicles.

Air suspension

A type of suspension that uses air springs instead of conventional steel springs. Computer operated vents on the air springs, suspension sensors and an onboard air compressor allow the system to maintain ride height and vary the suspension's ride characteristics.

All-wheel drive (AWD)

These drive system features four, full-time active drive wheels to reduce wheel slippage and provide greater driver control over the vehicle. AWD is operational at all times.

Alloy wheel

A generic term used to describe any non-steel road wheel usually cast as one piece. The usual alloys are either aluminum or magnesium.

Anti-dive

A tuned-in front suspension characteristic that converts braking-induced forces in the suspension links into a vertical force that tends to lift the body, thereby reducing dive under braking.

Anti-lock Brake System (ABS)

A computer, sensors, and solenoid valves work together to sense wheel speed in order to modulate braking force if any of wheels lockup during braking.

anti-roll bar

stabilizer bar

sway bar

It is a part of an automobile suspension that helps reduce the body roll of a vehicle during fast cornering or over road irregularities. It increases the suspension's roll stiffness (its resistance to roll in turns), independent of its spring rate in the vertical direction.

Anti-slip-control (ASR)

ASR is fitted to vehicles to prevent wheels slipping, spinning on slippery or uneven surfaces.

Anti-squat

A tuned-in rear suspension characteristic that converts accelerating-induced forces in the suspension links into a vertical force that tends to lift the body, thereby reducing squat under acceleration.

Alignment

When all wheels on the vehicle are adjusted so that they are pointed in the optimum direction relative to the road and each other.

Automatic level control

A component of the suspension which raises or lowers either (or both) the front or rear of the vehicle when there is a change in the amount of load in the vehicle.

Automatic ride control

Electronically operated soft or firm ride as required. It adjusts vehicle shock absorber resistance (damping) in response to driver inputs such as steering and braking and for changes in road surface.

Auxiliary leaf

An extra leaf in a set of leaf springs. Also called helper leaf or helper spring.

Ball joints

It is part of suspension mechanism, linking the knuckle with the control arms.

Beam Axle suspension

This system is used in front wheel drive cars, where the rear axle isn't driven. Another variation on this system does away with the springs and replaces them with torsion bars running across the chassis, and attached to the leading edge of the control arms.

Body roll

The leaning or tipping of a vehicle's body to one side when turning sharply. Body roll is controlled primarily by a sway bar, but the stiffness of the springs and shocks also play a role.

Bump-stop

It protects the suspension and vehicle (as well as the occupants) from violent "bottoming" of the suspension, caused when an obstruction (or hard landing) causes the suspension to run out of upward travel without fully absorbing the energy of the stroke.

Bounce

A state in which a vehicle moves up and down in the vertical direction, in a rotation about the lateral (left to right) axis about an oscillation center, where the oscillation center is outside the wheelbase.

Bushing

A bushing or rubber bushing is a type of vibration isolator. It provides an interface between two parts, damping the energy transmitted through the bushing. A common application is in vehicle suspension systems.

Camber

A wheel’s inward or outward tilt from vertical, measured in degrees. The camber angle is adjusted to keep the outside tires flat on the ground during a turn.

Camber Thrust

Side or lateral force generated when a tire rolls with camber, which can add to or subtract from the side force a tire generates.

Caster

The angle between a line drawn vertically through a wheel’s centerline and the axis around which the wheel is steered; improves a car’s directional stability and on-center feel.

Center of gravity (CG)

Also called center of mass. Center of gravity location can be defined as: The balance point of an object, or the point through which a force will cause pure translation, or the point about which gravity moments are balanced

Center of gravity height

The distance between the center of gravity and ground.

Centripetal force

In the case of an object moving in a circular path, the net force is a special force called the centripetal force Centripetal is Latin for "center seeking". So a centripetal force is a center seeking force which means that the force is always directed toward the center of the circle. Without this force, an object will simply continue moving in straight line motion

Centrifugal Force

The sideways acceleration, measured in g’s, of an object in curvilinear motion. As a car traverses a curve, centrifugal force acts on it and tries to pull it outward. To counteract this, the tires develop an equal and opposite force acting against the road. Also called lateral force.

Coilover shock absorber

A shock absorber that includes a coil spring and an adjustable coil spring seat. The adjustment increases or decreases firmness and ride height.

Coil Spring

A type of spring made of wound heavy-gauge steel wire used to support the weight of the vehicle. The spring may be located between the control arm and chassis, the axle and chassis, or around a MacPherson strut.

Compression Stroke (Jounce)

The shock or strut shaft traveling into/toward the body of the unit, like when hitting a bump.

Contact Patch

The contact patch is the area of contact between the ground and the tire. This parameter changes with many factors including tire pressure and wheel loads

Control arm (wishbone)

It is part of suspension mechanism, it is a nearly flat and roughly triangular suspension member (or sub-frame), that pivots in two places. The base of the triangle attaches at the frame and pivots on a bushing. The narrow end attaches to the steering knuckle and pivots on a ball joint.

Cornering Force

The force on a turning vehicle’s tires - the tire’s ability to grip and resist side force - that keeps the vehicle on the desired arc.

Curb Weight

Weight of a production vehicle with fluid reservoirs (including fuel tank) full and all normal equipment in place, but without driver or passengers.

Damper

A generic name for any device (shock, strut, cartridge, stabilizer, etc.) who's primary function is to resist movement, control movement oscillations.

Damping force

The effect or amount of resistance to movement.

De Dion Axle

A rear axle setup, which the driving wheels are attached to curved dead axle that is attached to the frame by a central pivot, the differential unit is bolted to the frame and is connected to the driving wheels by drive axles using Universal joints. The De Dion system keeps the wheels upright. Total unsprung weight is lower than a live axle, and is comparable to independent suspension.

Deflection

The movement of a suspension piece when subjected to a load.

Dependent suspension

It normally has a beam (a simple 'cart' axle) or (driven) live axle that holds wheels parallel to each other and perpendicular to the axle.

Directional Stability

The ability of a vehicle to be driven safely and with confidence in a straight line and at high speed without being affected by pavement irregularities, crosswinds, aerodynamic lifting forces, or other external influences.

Dive,

Forward pitch

Forward pitch is known as DIVE, which occurs as a result of braking. It is the opposite of squat, the dipping of a car's nose that occurs when the brakes are applied. Dive is caused by a load transfer from the rear to the front suspension. Also known as nose dive.

Drift

As a car loses traction in a turn it moves toward the outside of the turn. This movement is called drift.

Droop Travel

Extension travel of the suspension. Also can be termed as the amount of available suspension travel in extension from ride height.

Double wishbone suspension systems

It is an independent suspension design using two (occasionally parallel) wishbone-shaped arms to locate the wheel. Each wishbone or arm has two mounting points to the chassis and one joint at the knuckle. The shock absorber and coil spring mount to the wishbones to control vertical movement. The shown three examples are all variations on the same theme.

Electromagnetic Suspension (EMS)

It is the magnetic levitation of an object achieved by constantly altering the strength of a magnetic field produced by electromagnets using a feedback loop.

Electronic Stability Control

A computerized technology that improves the safety of a vehicle's stability by detecting and minimizing skids. ESC systems exist under many trade names, including Vehicle Stability Control (VSC), Electronic Stability Program (ESP), and Vehicle Stability Enhancement (VSE).

Extended length

A measurement of total length when the shock or strut shaft is fully extended. The measuring points are determined by the style of mountings.

Eye ring

A metal band that houses a mounting bushing. A shock or strut structural component.

Force

A force is any influence that causes an object to undergo a certain change, either concerning its movement, direction, or geometrical construction. In other words, a force can cause an object with mass to change its velocity (accelerate), or a flexible object to deform, or both.

Fore-and-Aft Weight Transfer

Transfer of weight from the front axle to the rear axle (or vice versa) caused by acceleration or braking. Acceleration causes weight transfer from the front axle to the rear axle. Braking causes weight transfer from the rear axle to the front axle.

Four-wheel drive (4WD)

In a Four Wheel Drive system, a secondary transmission assembly, called a transfer case, is driven from the main transmission. The transfer case distributes power to both axles to drive all four wheels. Four-Wheel Drive can be full-time, in which power is delivered to both axles at all times, or part-time where the driver selects two or four wheel drive.

Front-wheel drive (FWD)

A drive system where the engine and transaxle components apply the driving force to the front wheels rather than the rear wheels.

Gas shock

Any shock or strut that uses pressurized Nitrogen gas instead of oxygen: In a twin tube design, a low pressure Nitrogen gas is used to reduce aeration. The monotube design has a seperate high pressure Nitrogen gas chamber that reacts to driving conditions.

Jounce

When you drive over a bump and the suspension is momentarily compressed, that's called jounce.

Jounce travel

Compression movement of suspension. Also can be termed as the amount of available suspension travel in compression from ride height.

Gross Axle Weight Rating (GAWR)

The maximum weight that can be distributed among the tires on a given axle.

Gross Vehicle Weight (GVW)

The weight of the vehicle and its contents (fluids, passengers, and cargo).

Gross Vehicle Weight Rating (GVWR)

The maximum weight allowed for the vehicle and its contents. This value is established by the vehicle manufacturer and can be identified on the vehicle door placard.

Ground clearance

Ground clearance can be defined as the space or distance from the lowest point of your vehicle to the level surface below it.

Heading/yaw angle

Also the yaw angle, describing the heading of a vehicle.

Helper spring

An additional spring device that permits a greater load on an axle.

Hotchkiss drive

It is a system of power transmission. It was the dominant form of power transmission for front-engine, rear-wheel drive layout cars in the 20th century.

Hub

The component that interfaces the rotating wheel and the stationary spindle. Wheel bearings are housed by this component.

Hydractive Suspension

It is a new automotive technology It is a development of the Hydropneumatic suspension design using additional electronic sensors and driver control of suspension performance. The driver can make the suspension stiffen (sport mode) or ride in outstanding comfort (soft mode).

Hydrolastic Suspension

It is a type of space-efficient automotive suspension system used in many cars. It is naturally a progressive spring-rate suspension. The system replaces the separate springs and dampers of a conventional suspension system with integrated, space efficient, fluid filled, displacer units, which are interconnected between the front and rear wheels on each side of the vehicle.

Hydragas suspension

The system uses nitrogen gas as the springing medium and hydraulic fluid pressure drop as the damping mechanism. The damping fluid chambers of the front and rear wheels on each side of the car are connected via a hydraulic hose, such that an input at the front wheel pumps fluid through the pipe to the rear wheel. The increase in fluid pressure at the rear unit creates an upward force on the sprung mass, thus reducing the differential between suspension forces on the front and rear of the car body. The difference between hydrolastic and hydragas is that the hydragas version uses pressurized nitrogen instead of a rubber spring.

Hydropneumatic suspension

Hydropneumatic suspension elements integrate a nitrogen spring within a monotube damping unit. It combines the excellent properties of gas springs with the favorable damping properties of hydraulic fluids.

Included angle

Included is summation of steer axis inclination/king pen inclination (SAI/KPI) to the camber angle. Also called steering knuckle angle.

Independent suspension

A suspension system that allows each wheel on a vehicle to move up and down independently of the other wheels.

Jacking forces

Jacking forces are the sum of the vertical force components experienced by the suspension links. The resultant force acts to lift the sprung mass if the roll center is above ground, or compress it if underground. Generally, the higher the roll center, the more jacking force is experienced.

Jounce

When you drive over a bump and the suspension is momentarily compressed, that's called jounce.

Kilopascal (kPa)

The metric unit for air pressure. One psi is equal to 6.9 kPa.

Knuckle

The part of suspension mechanism on which the wheel and of the braking and steering system are installed.

Lateral weight transfer

When a vehicle travels through a curve, weight is transferred from the wheels on the inside of the curve to the wheels on the outside of the curve. This is a result of the centrifugal force, or lateral force acting on the vehicle.

Leaf spring

A type of spring made out of a flat strip or individual leaves to support the weight of a vehicle. Most are steel, but some are made of lightweight composite materials

Limiting strap

It is a simple strap, often nylon of a predetermined length, used in many off-road vehicles, to limit the suspensions downward travel to a point within safe limits for the linkages and shock absorbers.

Longitudinal leaf spring

A Leaf spring that is mounted so that it is parallel to the length of the vehicle.

Tire longitudinal skid/slip

It is defined as a difference between the tire tangential speed and the speed of the axle relative to the road.

MacPherson strut

A suspension system that consists of a combination coil spring and shock absorber (strut) in one compact unit at each wheel. With this "independent" suspension design, road shocks at one wheel are not transferred to the opposite wheel. MacPherson struts use fewer parts, meaning a reduction on weight and fewer elements that could wear out.

magnetorheological damper, magnetorheological shock absorber

It is a damper filled with magnetorheological fluid, which is controlled by a magnetic field, usually using an electromagnet. This allows the damping characteristics of the shock absorber to be continuously controlled by varying the power of the electromagnet.

Mini-strut (spring seat shock)

Sometimes called a spring seat shock: A shock absorber that includes a mounting area for a coil spring. Sometimes called a spring seat shock: A shock absorber that includes a mounting area for a coil spring. This does not eliminate an upper control arm.

Mono-tube

Monotube

A damping unit design that has a mono-tube, the shell case itself works as a cylinder and oil, gas, piston valve, etc are all set in a single tube. Mono-tube uses a free piston that completely separates the oil chamber from the gas chamber. . The gas area acts as the fluid expansion area and provides additional damping on demand.

Negative camber

Alignment setting where the tops of the tires are leaning toward the centerline of the vehicle; racers use a negative camber angle for maximum cornering potential.

Nivomat

A trademarked type of shock absorber that controls ride height. (self-leveling) It contains a mechanical hydraulic pump activated by vehicle movement.

Nose Dive

Occurs during vehicle braking: The front of the vehicle surges downward and the rear of the vehicle surges upward.

Non-serviceable struts

A sealed strut that does not have a replaceable cartridge. This unit must be replaced as an assembly.

Outboard Assembly

The components that lie outside of the arms or other “linking” members. Usually including: suspension upright, steering arm, hub, brake mount and caliper assembly, rotor, and the wheel

Oversteer

The tendency for a vehicle, when negotiating a corner, to turn more sharply than the driver intends. The rear end of the vehicle wants to swing toward the outside of a turn. A handling condition in which the slip angles of the rear tires are greater than the slip angles of the front tires. An oversteering car is sometimes said to be “loose,” because its tail tends to swing wide.

Pitching

It is a rotation about the lateral (left to right) axis about an oscillation center, where the oscillation center is inside the wheelbase.

Polar moment of inertia

The tendency of a vehicle to resist cornering (angular or rotational acceleration).

Positive camber

Alignment angle that makes the top of the tires farther apart than at the bottom; tires are tilted out from the centerline of the vehicle.

Positive caster

Alignment setting when the steering axis is inclined rearward at the top.

Progressive-rate spring

A spring used in a vehicle that stiffens under load.

Pull

A condition in which a vehicle swerves to one side without being steered in that direction, as a result of irregular tire wear, improper front and/or rear wheel alignment, or worn or improperly adjusted brakes

Rear wheel drive (RWD)

A drive system where the engine applies the driving force to the rear wheels only. This pushes the vehicle from the rear wheels.

Rebound stroke

The motion of a wheel that extends the suspension. The opposite of jounce or compression stroke.

Ride control

Four separate vehicle systems (Tires, suspension, steering & brakes) that work together to control a vehicle's stopping, turning, handling, stability control and ride comfort.

Ride height

The distance from the ground to a fixed reference point (differs by automaker) on the vehicle’s body. This dimension can used to measure the amount of suspension travel or the height of the body from the ground.

Ride rate

The effective stiffness of the suspension and tire springs in series.

Roll

The rotation of the vehicle's body around its center point as viewed from front. When a vehicle enters a turn, it experiences a roll.

Roll axis

The roll axis is simply a line joining the front roll center with the rear roll center, in other words the axis about which the vehicle rolls

Roll center

The roll center of a vehicle is the notional point in the transverse vertical plane through any pair of wheel centers at which the cornering forces in the suspension are reacted to the sprung mass of vehicle body.

Roll center arm

It is the distance between the center of gravity and the roll center.

Rollover

A rollover is a type of vehicle accident in which a vehicle tips over onto its side or roof.

Roll rate

Actions that include lateral accelerations, causing a vehicle's sprung mass to roll about its roll axis. It is expressed as torque per degree of roll of the vehicle sprung mass. It is influenced by factors including but not limited to vehicle sprung mass, track width, CG height, spring and damper rates, roll center heights of front and rear, anti-roll bar stiffness and tire pressure/construction.

Rubber suspension

(Moulton rubber suspension)

This suspension system is based on the compression of a solid mass of rubber.

Scrub Radius

Scrub radius is the distance between where the SAI intersects the ground and the center of the tire. Scrub radius is designed at the factory and is not adjustable.

Self-aligning torque

The restoring force of a tire at the center of the footprint when subjected to a side force, as when cornering; this attempt to reduce the slip angle by the tire makes the steering feel heavy to the driver.

Self-leveling shock

A damping unit that automatically adjusts suspension balance and height to keep the vehicle level in all driving conditions.

Self-leveling suspension

A system that maintains a constant ride height of the vehicle above the road, regardless of load.

Serviceable strut

A strut assembly that is designed with a replaceable cartridge. Some designs have an upper hex nut while others require a special cutting tool.

Set back

Set back is when one front wheel is set further back than the other wheel.

Shock

:A term used for shock absorber.

Shock absorber

A fluid type cylinder which stops the car from bouncing after the initial shock has been absorbed by the spring. It converts motion into heat, usually by forcing oil through small internal passages in a tubular housing to dampen suspension oscillations. Most cars have four shock absorbers.

Shock fade

A condition where loss of dampening action occurs because of fluid foaming inside a shock absorber. The rapid oscillations of the piston moving through the fluid churns it into foam, which reduces the amount of resistance encountered by the piston. This causes the dampening action to fade, resulting in loss of control, excessive suspension travel and reduced handling.

Shock travel

The measurable difference between the extended and compressed lengths of a shock or strut.

short long arms suspension (SLA)

It is also known as an unequal length double wishbone suspension. A Suspension system using an upper and lower control arm. The upper arm is shorter than the lower. This is done so as to allow the wheel to deflect in a vertical direction with a minimum change in Camber.

Skid

To slip or slide on the road when tires lose their rolling grip.

Slip

The difference between the linear speed of the vehicle and the rotational speed of the tire. For example, if a tire is locked and sliding (e.g., not rotating) while the vehicle is still moving, then it is operating at -100% slip.

Slip angle

The difference between the direction the wheel is traveling and the direction the vehicle is traveling.

squat

The opposite of dive, squat is the dipping of a car's rear end that occurs during hard acceleration. Squat is caused by a load transfer from the front to the rear suspension. An anti-squat system incorporated with the rear suspension to reduce the car squat when accelerating.

Solid-axle, coil-spring

The drive axle housing is clamped to the coil springs and the shock absorbers normally bolt directly to the axle, or the 'coil-over-oil' spring and shock combos. A pair control arms gives the support to the assembly. The front ends of these are attached to the chassis, the rear ends to the axle.

Solid-axle, leaf-spring

The drive axle housing is clamped to the leaf springs and the shock absorbers normally bolt directly to the axle. The ends of the leaf springs are attached directly to the chassis, as are the tops of the shock absorbers.

Spring rate

It is the amount of weight needed to compress a spring a certain distance. Springs are rated in N/mm, or specifically, how many kg of weight or force (N) are required to depress the spring by one mm.

Spring compressor

A tool for compressing and holding a coil spring so it can be removed or replaced, or to allow the disassembly of a MacPherson strut.

Spring seat

The mounting area for a suspension coil spring. This may be located on the vehicle or on the damping unit.

Sprung mass/weight

The mass/wieght of the body and other components supported by the suspension is the sprung mass. It is the portion of the vehicle's total mass/weight that is supported above the suspension, including in most applications approximately half of the weight of the suspension itself. The sprung weight typically includes the body, frame, the internal components, passengers, and cargo, but does not include the mass of the components suspended below the suspension components.

Stability control

A type of advanced antilock brake/traction control system that uses the brakes to assist steering maneuvers and to help improve vehicle handling and stability as driving conditions change.

Steer axis inclination (SAI)

Measured in the front view, the angle between the vertical and an axis defined by the upper and lower ball joints. SAI is also referred to as KPI (King Pin Inclination) on trucks and old cars with kingpins instead of ball joints. SAI urges the wheels to a straight ahead position after a turn.

The steering angle

It is defined as the angle between the front of the vehicle and the steered wheel direction.

Steering damper (stabilizer)

A hydraulic device similar to a shock absorber attached to the steering linkage to absorb road shock and steering kickback.

Steering response

A vehicle’s reaction to a driver’s steering inputs. Also the feedback that drivers get through the steering wheel as they make steering inputs.

Steering system

The entire mechanism that allows the driver to guide and direct the vehicle; includes the steering wheel, steering column, steering gear, linkages, and wheel supports.

Suspension

The various springs, shock absorbers and linkages used to suspend a vehicle’s frame, body, engine, and drivetrain above its wheels and allows relative motion between the two.

Strut

A suspension strut combines the primary function of a shock absorber (as a damper), with the ability to support sideways loads not along its axis of compression, thus eliminating the need for an upper suspension arm.

Sway bar

A component that's often used in a suspension system to control body roll. A sway bar may be used on the front and/or rear suspension to help keep the body flat during cornering/maneuvering.

Thrust angle

Thrust angle is the direction that the rear wheels are pointing in relation to the center line of the vehicle.

Tie rod

A part of the steering linkage that connects the steering arms on the knuckles to the steering rack or center link.

Toe

The difference in distance between the front and rear of a pair of tires mounted on the same axle.

Toe-In

The fronts of two tires on the same axle are closer than the rears of the tires.

Toe-Out

The fronts of two tires on the same axle are further apart than the rears of the tires.

Toe-Out Turns

Also known as Ackerman Angle. A vehicle’s wheels on the inside of a turn follow a smaller radius than the tires on the outside of the turn, because the two front wheels steer at different angles when turning.

Torque

Turning or twisting effort, usually measured in lb-ft or Newton meters.

Torsion Bar

A long, straight bar fastened to the frame at one end and to a suspension part at the other; acts like an uncoiled spring that absorbs energy by twisting.

Track

The distance from centerline to centerline of the vehicle's tires on the same axle.

Traction

The friction between the tires and the road surface; the amount of grip provided.

Tramping

A state in which a vehicle bounces up and down abnormally.

Trailing arm

A suspension element consisting of a longitudinal member that pivots from the body at its forward end and has a wheel hub rigidly attached to its trailing end.

Transverse leaf-spring suspension

it involves one leaf spring mounted across the vehicle, connected at each end to the lower wishbone. The center of the spring is connected to the front subframe in the middle of the car. There are still two shock absorbers, mounted one to each side on the lower wishbones.

Travel limiting bumper

A protective insulator to avoid damage when the suspension bottoms-out. Usually a (separate or as part of the strut boot) polyfoam bushing on a strut shaft or a rubber-like cushion mounted on the vehicle frame above a front or rear axle.

Travel (suspension)

It is the measure of distance from the bottom of the suspension stroke (such as when the vehicle is on a jack and the wheel hangs freely) to the top of the suspension stroke (such as when the vehicle's wheel can no longer travel in an upward direction toward the vehicle)

Twin I-Beam

A type of independent front suspension used on Ford pickup trucks that used two parallel I-beam axles (one for each wheel).

Twin-tube

A damping unit design that has two concentric tubes: An inner working cylinder and an outer fluid reservoir. The inner, or working cylinder, is where the piston and shaft move up and down. The outer cylinder serves as a reservoir for the hydraulic fluid. There are fluid valves in the piston and in the stationary base valve. The base valve controls fluid flow between both cylinders and provides some of the damping force. The valves in the piston control most of the damping.

Understeer

The handling characteristic in which the front tires break loose because they are running a larger slip angle than the rear tires. Also known as plowing.

Unequal-length wishbone suspension

A double wishbone suspension system in which the upper wishbone is shorter than the lower one, with both converging slightly at the wheel hub; reduces tire wear due to variations in track and camber angle when cornering

Unsprung Weight/mass

The weight/mass of the parts of a vehicle not supported by its springs, including wheels and tires, outboard brake assemblies, the rear axle assembly, suspension members, springs, shock absorbers and anti-roll bars.

Upright

Mounted vertically (upright) between the upper and lower control arm’s outer rod ends. The upright is the foundation of all outboard systems: the spindle and calipers are mounted directly to it.

Variable Rate Spring

Spring the deflection of which is not linear to the load applied.

Variable Ride-Height Suspension (VRHS)

Depending on conditions such as vehicle speed and terrain, Variable Ride-Height Suspension (VRHS) raises or lowers the ride height of the vehicle while it is in motion.

Vertical Bouncing

Vertical bouncing, or static imbalance, exists when the weight is not evenly distributed around the wheel’s axis of rotation. You can feel this through the floor, seat and steering column.

Weight Distribution

This is the amount of weight on the front and rear axles expressed as percentages.

Weight transfer

Depending on conditions such as vehicle speed and terrain, Variable Ride-Height Suspension (VRHS) raises or lowers the ride height of the vehicle while it is in motion. Some VRHS systems operate automatically, while others require the driver to select the appropriate mode.

Wander

A vehicle’s tendency to stray or wander from its intended direction of travel as a result of steering abnormalities, worn tires, suspension misalignment, crosswinds, or pavement irregularities.

Weight transfer

Weight transfer during cornering, acceleration or braking is usually calculated per individual wheel and compared with the static weights for the same wheels. The total amount of weight transfer is only affected by four factors: the distance between wheel centers (wheelbase in the case of braking, or track width in the case of cornering) the height of the center of gravity, the mass of the vehicle, and the amount of acceleration experienced

Wheel Alignment

Refers to the proper angle settings of suspension components as they relate to the angles of the wheels so they are perpendicular to the ground and parallel to each other so as to help prolong tire life and provide dead straight tracking on straight and level roads. Related terms include camber, caster and toe.

Wheel balance

The even distribution of weight around a wheel so that it rotates without vibrating or shaking. It is achieved by positioning weights on the rim that offset heavy spots on the wheel and tire assembly.

Wheelbase

The longitudinal distance from the center of the front wheel to the center of the rear wheel on the same side of the vehicle.

Wheel rate

Is the effective spring rate of the suspension when force

is applied at the wheel. This parameter is calculated from the spring rate through geometry of the suspension out to the wheel.

Yaw

The rotation of the vehicle's body around its center point as viewed from above. When a vehicle enters a turn or makes a sudden lane change, it experiences a change in yaw.

Yaw/heading angle

The angle of deviation between a vehicle's longitudinal axis and its true direction of motion, i.e., the difference between the direction a vehicle is pointing when cornering and the direction in which it is actually moving.

Yaw sensor

A yaw sensor in the ABS stability control system senses this change to determine if the vehicle is experiencing understeer or oversteer.

Zero toe

When tires on the same axle are parallel; the fronts and rears of the tires are equidistant.