Chevrolet Trax: Automotive terminology & definitions

ACTIVE SUSPENSION SYSTEM

active suspension systems move each wheel up and down to control body motion in response to road abnormalities. The system responds to inputs from the road and the driver. With an active suspension, a vehicle can simultaneously provide the smooth ride of a soft suspension along with the superior handling associated with a firm suspension.

ACTIVE TILT CONTROL

active tilt control winds up the stabilizer bars in the front and rear suspension to resist body lean while cornering. Because active control is used only as needed, vehicle spring rates and stabilizer bar stiffness can be reduced, improving normal ride characteristics. In addition, this system has potential to increase low-speed, off-road traction on 4WD vehicles.

ACTIVE VARIABLE RATIO STEERING

electronically provides variable steering ratios. A computer is linked with the vehicle stability control system to aid in directional stability of the vehicle. As the vehicle travels down the highway, road surfaces and wind gusts can affect the vehicle directional stability. The car may wander a little or dart to one side, as many who have met a tractor-trailer unit on a windy day have experienced. Sensors on the car detect this sudden unintentional movement and the computer will stabilize the car by moving the Active Steering electric motor and steering gear. The driver doesn't turn the steering wheel at all.

AIR SPRING

a suspension device made up of a flexible bladder containing compressed air. The air spring takes the place of a :onvent;onal coil or leaf spring. Air is supplied by an on-board ;ompressor, usually with auxiliary equipment to sense vehicle leight and modify the pressure in the air spring as needed.

AIR SUSPENSION

instead of steel coil or leaf springs, some vehicles have a bellows-like unit at each corner that contains pressurized air. As a rule, air suspensions can produce a softer ride.

ALIGNMENT

an adjustment to bring parts or components into a line or proper coordination.

ALL-WHEEL DRIVE

the method of providing traction to any of the wheels of a vehicle, as conditions require. Depending on the system, it may be full-time or part-time.

ANTI-ROLL BAR

see 'stabilizer bar'.

ASPECT RATIO

the relationship between the height of a tire from bead to tread, and the tread width, usually expressed as a percentage of the tread width.

AUTOMATIC RIDE CONTROL

automatic ride control adjusts vehicle shock absorber resistance (damping) in response to driver inputs such as steering and braking and for changes in road surface. During maneuvers such as hard braking or quick lane changes, the system increases suspension damping to improve dynamic stability. Damping is automatically decreased during steady driving, so that bumps and potholes are absorbed rather than being transmitted to the occupants. Some systems also allow the driver to select suspension settings: soft, normal or firm (sport).

AXIAL LOAD

a type of load placed on a bearing that is parallel to the axis of the rotating shaft.

AXIAL PLAY

movement of a component parallel to the axis of rotation.

AXIAL

round, on or along an axis; having the same direction or being parallel to the axis of rotation.

AXIS

a real or imaginary straight line on which or around which an object rotates.

BALANCE

a condition of equal weight distribution within a component or among components; the act of equalizing the weight distribution, such as balancing a tire or an engine's reciprocating assembly.

BALL JOINT

a suspension component that provides a pivot point, allowing the steering knuckle to move up and down as well as turn. In response to steering input. The ball fits into a socket housing that is attached to the control arm and the stud on the other end of the ball is attached to the steering knuckle. A dust cover is installed over the ball and socket assembly to keep dirt out and lubricant in.

BEAD

the steel reinforced inner edge of a tire, which fits inside and seals against the wheel rim.

BOOT

protective rubber cover with accordion pleats used to contain lubricants and exclude contaminating dirt, water and grime, located at each end of the rack-and- pinion assembly and FWD CV-joints.

BUMP STEER

a steering problem in which a vehicle tends to the left or the right after a bump, without steering wheel input from the driver. This is usually caused by some steering misalignment or damage that permits change of toe when the suspension works up and down.

BUSHING

a liner, usually removable, for a bearing; an anti-friction liner used in place of a bearing; a type of bearing that is used to support rotating shafts.

CAMBER

the attitude of a wheel/tire assembly in which, when viewed from the front, the distance between the tops and bottoms of the tires are different. If the distance between the tops is greater than between the bottoms, positive camber is present. If the distance between the tops is less than between the bottoms, negative camber is present.

CASTER

angle formed between the kingpin axis and a vertical axis as viewed from the side of the vehicle. Caster is considered positive when the top of the kingpin axis is behind the vertical axis, that is, tilted toward the rear of the vehicle.

CENTER LINK

a steering linkage component which attaches the Pitman arm to the idler arm, tie-rod or crosslink.

COIL SPRING

spring steel rod wound into a coil that supports the vehicle's weight while allowing suspension movement.

COLLAPSIBLE STEERING COLUMN

a steering column that is designed to collapse, to prevent the column from heavily impacting the driver during an accident.

CONSTANT VELOCITY (CV) JOINT

a flexible coupling between two shafts that allows each shaft to maintain the same speed regardless of operating angle.

CONTROL ARM

a suspension component that connects the vehicle frame to the steering knuckle or axle housing and allows the up and down movement of the wheels.

COTTER PIN.

a safety component made from soft steel, used to keep a nut from loosening on a bolt or stud. The cotter pin is inserted through a hole in the bolt or stud and through slots in the nut (see 'castellated nut'), then the ends of the cotter pin are spread to lock it in position.

CROSSMEMBER

part of the vehicle frame structure, arranged transversely and attached to the frame rails at each side of the vehicle. Can be removable or welded in place.

DAMPEN

to slow or reduce oscillations or movement.

DEAD AXLE

a load-supporting axle that does not transmit power; an axle that does not rotate, but merely forms a base on which to attach the wheels.

DIRECTIONAL STABILITY

the ability of a car to travel in a straight line on a flat surface with a minimum of driver control.

DIRECTIONAL TIRE

tire with a tread pattern that is designed to give maximum traction by removing water from under the tread in such a way as to minimize the risk of aquaplaning. Directional tires must be installed to turn in a specific direction.

DOWNFORCE

negative aerodynamic lift.

DRAG COEFFICIENT

drag divided by the product of dynamic pressure and projected area. A factor representing the drag acting on a body (as an automobile or airfoil).

DRAG LINK

a steering linkage component that connects the pitman arm and the steering arm.

DRAG

horizontal aerodynamic retarding force on a vehicle parallel to the relative wind direction.

DYNAMIC BALANCING

balancing a part while it is in motion.

ELECTRICALLY POWERED STEERING

electrically powered steering uses an electric motor to drive either the power steering hydraulic pump or the steering linkage directly. The power steering function is therefore independent of engine speed, resulting in significant energy savings.

ELECTRONIC AIR SUSPENSION

electronic air suspension provides the comfort of riding on air with adjustable spring rates and capability to change ride height and load-carrying ability. Under normal driving conditions, an electronic air suspension vehicle rides at the same height as a traditionally sprung vehicle. With a heavy load, ride height is increased automatically. On current vehicles, the suspension lowers the ride height by 20 mm at highway speeds for improved aerodynamics, with about 2 percent better fuel economy. Lower ride height also can improve on-center feel of steering due to the change in suspension geometry and increased caster angle.

ELECTRONIC LEVEL CONTROL

a suspension system that uses air springs to maintain vehicle ride height. Height sensors are used to signal a control unit when the vehicle is riding low or high. In response to this signal, compressed air is either sent to or vented from the air springs.

HALFSHAFT

transfers power from the transaxle to the front wheels on a front-wheel drive vehicle. Also used on some vehicles with rear-wheel drive and independent rear suspension to transfer power from the differential to the rear wheels. Consists of a stub shaft that is splined into the differential side gear, another stub shaft that is splined into the wheel hub, an interconnecting shaft, and two CV-joints, which connect the interconnecting shaft to the stub shafts.

HARMONIC VIBRATION

periodic motion or vibration along a straight line. The severity depends on the frequency or amplitude.

HEIGHT SENSOR

a component used in an air suspension system to signal a control unit when the vehicle is riding low or high. In response to this signal, compressed air is either sent to or vented from the air springs.

HUB

mounting point for the wheelan an axle or spindle; the part of the synchronizer assembly that is splined to the transmission shaft; the center part of a wheel, gear, etc., that rides on a shaft.

IDLER ARM

a conventional steering system component consisting of an arm that swivels in a bushing on a shaft, which is attached to the frame. The idler arm is mounted on the right side of the vehicle and is the same length and set at the same angle as the Pitman arm. Its function is to hold the right end of the center link level with the left end, which is moved by the pitman arm, and transfer the steering motion to the right side tie-rod.

INCLUDED ANGLE

the sum of the angle of camber and steering axis inclination; the sum of two intersecting angles.

INDEPENDENT SUSPENSION

a suspension in which each wheel can travel up and down without directly affecting the position of the opposite wheel.

INTEGRAL POWER STEERING

a power steering system in which the power cylinder and control valve are contained in one housing.

INTELLIGENT VEHICLE HIGHWAY SYSTEM (IVHS)

the Intelligent Vehicle Highway System (IVHS) provides a variety of information to the vehicle and driver through cooperation of automotive electronics, communications, controls and systems engineering technologies. IVHS has two areas of interest to car and truck makers: (1)telematics and (2)active safety warning and control systems. Several features are: Telematics: Navigation systems Traffic messaging Emergency messaging and security tracking (e.g. RESCU - Remote Emergency Satellite Cellular Unit) Short range communications/ automatic toll collection Active Safety Warning and Control Systems Collision warning/avoidance - Backup and parking aids - Side vision aid - Vision enhancement - (all weather/night vision) - Adaptive cruise control - Lane departure control

INTERACTIVE VEHICLE DYNAMICS (IVD)

interactive Vehicle Dynamics is designed to minimize loss of vehicle control due to loss of traction. The IVD system could be activated when a vehicle is taking a turn too quickly or when encountering an icy patch.

JAM NUT

a locknut.

KINGPIN

the pivot shaft for the steering knuckle on most early axles and some modern heavy-duty axles.

KNUCKLE

the suspension component that connects the upper and lower control arms or the strut and lower control arm. On rear wheel drive vehicles, it usually incorporates the front wheel spindle and on front wheel drive vehicles it has an opening where the halfshaft passes through. A steering arm is attached to the knuckle, where the tie-rod end is connected. Also called a steering knuckle.

LANE-DEPARTURE WARNING SYSTEM

Issues a warning when the vehicle edges off course and reaches the highway lane markers. Introduced on the 2005 Infiniti FX and available on the 2006 Infiniti M45, the system developed by Iteris can detect lane dividers even in rainy weather. It delivers a noticeable sound when the vehicle starts to move into an adjacent lane, whether due to inattention, drowsiness or distraction.

LATERAL RUNOUT

side-to-side movement or wobble in a wheel or tire.

LEAF SPRING

a suspension spring consisting of a single flat plate made of steel or composite material or several steel plates bundled together.

LOW TIRE PRESSURE WARNING

a low tire pressure warning system alerts the driver if the air pressure in a tire becomes too low.

Typically, a light on the instrument panel will be illuminated to warn of the low-pressure condition.

MACPHERSON STRUT

the principal device in the suspension of the same name, in which the spring, shock absorber and sometimes the steering knuckle are combined in a single unit.

MEMORY STEER

a steering condition where the steering wheel and wheels want to return to a position other than center.

This can be caused by tightening rubber bonded socket tie-rod ends when the steering wheel is not centered, binding in the upper strut mounts, or binding in a steering component or ball joint.

ON-CAR BALANCING

the practice of spinning a wheel on the car to balance the wheel and all other rotational components together.

PARALLELOGRAM STEERING LINKAGE

a type of conventional steering linkage consisting of a pitman arm, center link, idler arm and tierod assemblies to connect to the steering knuckles. The pitman arm, center link and idler arm form three sides of a parallelogram.

PITMAN ARM

a steering system component mounted on the steering box shaft and transfers the gearbox motion to the steering linkage.

PLUNGER JOINT

the inboard CV-joint on a halfshaft, so called because the joint moves in and out in response to the suspension's up and down movement, which causes the distance between the transaxle and the wheel to change. The movement takes place within the joint, with the tripod rollers or double offset ball bearings moving in and out on elongated grooves in the yoke or outer race.

PRESS FIT

when a part is slightly larger than a hole it must be forced together with a press.

PULL

a steering condition where the vehicle driver has to maintain constant pressure on the steering wheel to keep the vehicle moving straight.

RACK-AND-PINION STEERING

a type of steering mechanism that replaces the pitman arm, center link and idler arm on gearbox steering.

The steering column ends in a pinion gear that moves the driven rack to the left and right. The rack ends contain ball studs connected to the outer tie-rod ends and steering knuckles.

RADIAL LOAD

load applied at 90 degrees to an axis of rotation.

RADIAL RUNOUT

the out-of-roundness ot a wheel or tire.

RADIAL

branching out in all directions from a common center; perpendicular to the shaft or bearing bore.

RADIUS ARM

a suspension component that is connected to a twin I-beam or solid axle at one end and to the vehicle frame through bushings at the other. The radius arm braces the I-beam or axle and keeps it at a right angle to the vehicle frame.

REAR WHEEL STEERING

a system used on a some vehicles to change the toe of the rear wheels to either steepen a sharp turn or enhance cornering on a shallower, faster one.

RIDE HEIGHT

the dimension between a fixed point on the vehicle and the pavement. The fixed point varies according to vehicle and manufacturer. Also called vehicle height.

ROLLING RESISTANCE

retarding force, parallel to the direction of travel, caused by tire resistance along the ground.

RUNOUT

wobble or deflection beyond a rotating part's normal plane of movement.

SAI

see 'steering axis inclination',

SCRUB RADIUS

the distance between the point at which the tire's vertical centerpoint intersects the road, and the steering axis inclination (SAI) intersects the road.

SHACKLE

the attachment to the frame for one end of a leaf spring. The shackle allows the spring to change in length as the vehicle encounters uneven road surfaces.

SHIM

thin sheets of material, usually metal, used as spacers to control the distance between parts.

SHOCK ABSORBER

a device used to dampen the oscillation of the suspension caused by irregularities in the road surface.

SHORT AND LONG ARM SUSPENSION

a suspension system in which the upper control arm is shorter than the lower control arm, allowing the wheel to deflect in a vertical direction with minimal change in camber.

SPINDLE

a shaft used to attach the wheel assembly on non-drive axles.

SPRING

a suspension system component that supports the vehicle and absorbs shock caused by uneven road surfaces; a device that returns to its original form after being forced out of shape.

SPROCKET

a toothed wheel used to engage a chain or ribbed belt.

SPRUNG WEIGHT

the weight of all the vehicle components that are supported by the springs; see 'unsprung weight'.

STABILIZER BAR

a torsion-bar spring connecting the suspension on either side of the vehicle. When a vehicle rolls to the side in a turn, the suspension at the outside wheel compresses and the suspension at the inside wheel extends. The stabilizer bar that connects them twists to apply a counteracting force to hold the vehicle closer to level. Also called an anti-roll bar or sway bar.

STATIC BALANCE

balance at rest; still balance; the equal distribution of weight of the wheel and tire around the axis of rotation such that the wheel assembly has no tendency to rotate by itself regardless of its position.

STEERING ARM

the steering system component that links the steering knuckle to the tie-rod assembly.

STEERING AXIS INCLINATION

the angle between true vertical and an imaginary line running through the rotational center of the ball joint(s).

STEERING COLUMN

the housing, steering shaft, bearings and related components between the steering wheel and the steering gear.

STEERING GEAR

the assembly located at the end of the steering column, which contains the gears and other components that multiply the driver turning force.

STEERING KNUCKLE

the suspension component that connects the upper and lower control arms or the strut and lower control arm. On rear wheel drive vehicles, it usually incorporates the front wheel spindle and on front wheel drive vehicles it has an opening where the halfshaft passes through. A steering arm is attached to the steering knuckle, where the tie-rod end is connected.

STEERING LINKAGE

all of the components that connect the steering gear to the front wheels.

STRUT ROD

on vehicles where the lower control arm is attached to the frame at one pivot point, a strut rod is used to brace the control arm against the vehicle frame.

STUD

a fastener that has screw threads at both ends.

SWAY BAR

see 'stabilizer bar',

THRUST ANGLE

the difference between the thrust line and the geometric centerline of the vehicle.

THRUST LINE ALIGNMENT

aligning the front wheels to the thrust line during a wheel alignment, when rear wheel toe cannot be adjusted to specification.

THRUST LINE

an imaginary line that divides the total toe angle of the rear wheels.

THRUST LOAD

load placed on a part that is parallel to the center of the axis.

TIE-ROD END

a ball and socket joint that connects the tie-rod to the steering knuckle arm and to the center link or steering rack.

TIE-ROD

steering linkage member which connects the steering knuckle arm with the centerlink or the steering rack.

TIRE ROTATION

the practice of moving a set of tires to different positions on the vehicle to equalize wear and extend the life of the tires.

TIRE SLIP

see 'wheel slip'.

TOE

the direction in which a wheel tends to roll, a major factor in tire wear.

TOE-IN

a condition that exists if the tire's line of forward direction intersects the extended centerline of the vehicle.

TOE-OUT ON TURNS

the designed angle of the steering arm on the steering knuckle, which causes the inside front wheel to turn at a sharper angle than the outside front wheel during a turn. The specification is checked using the turntables on wheel alignment machine. Toe-out on turns is not an adjustable angle, and if it is incorrect it is most likely due to a bent steering arm.

TOE-OUT

a condition that exists if the tire's line of forward direction and the vehicle centerline are angled apart.

TRACK

the distance between the centers of the treads of parallel wheels.

TRACKING

travel of the rear wheels in a parallel path with the front wheels.

TWIN I-BEAM SUSPENSION

a type of independent front suspension and used on light trucks and vans. It consists of two I-beams supported by coil springs, and the steering knuckles/spindles, which are connected by king pins or ball joints. The inner end of the axle connects to the vehicle frame through a rubber bushing. A radius arm also connects to the frame through rubber bushings to control wheelbase and caster.

UNSPRUNG WEIGHT

the components of a vehicle that rest directly on the road surface without being supported by the suspension springs.

VARIABLE ASSIST POWER STEERING

a power steering system that uses valves and speed sensors to vary the amount of steering assist according to engine or road speed. At slow speeds more steering assist is delivered and steering the wheels is easier; necessary for parking, etc.. At higher speeds, steering assist is reduced and more steering effort is required to steer the car, giving the driver greater feel of the road. Also known as Speed-sensitive power steering.

VEHICLE HEIGHT

see 'ride height'.

WHEEL ALIGNMENT

the adjustment of suspension and steering components to optimize steering control and minimize tire wear.

WHEEL BALANCE

the condition in which a wheel/tire assembly has equal weight around its center, preventing vibration at high speeds. Wheel balance can be static, such as on a bubble balancer, or dynamic, such as with a spin balancer.

WHEEL OFFSET

the dimensional difference between a wheel's centerline and the plane of the axle flange mounting surface.

WHEEL SLIP

a measurement (in percentage) of the friction between the tire and road surface; at zero slip the tire rotates freely, while at 100% slip the tire is locked up and is pushed along the road surface by the moving vehicle. Also called tire slip.

WHEEL SPEED SENSOR

a permanent magnetic sensor that sends information to the computer in an ABS system regarding wheel speed.

WHEEL WEIGHTS

small weights, usually made of lead, attached either mechanically or by adhesive to a wheel/tire assembly to correct its balance.

WORM GEAR

a gear into which teeth are cut, resembling the threads of a screw.

READ NEXT: