Mechanical Engineering Dictionary-Automotive Vehicles

Important Terms and their Meaning of Mechanical Engineering-Automotive Vehicles:

ACCELERATOR – A pedal connected to the carburettor throttle valve of a motor vehicle or to the fuel injection control where oil engines are used.

ACKERMAN PRINCIPLE – Steering geometry in which the outer ends of the steering arms are bend slightly inward so that when the vehicle is making a turn, inside wheel will turn more sharply than the outer wheel. This principle produces toe out on turns.

ACKERMAN STEERING – Arrangement whereby a line extended from the track arms, when the wheels are set straight ahead, should meet on the chassis centre line at 2/3 of the wheel base from the front, allowing inner stub axle to move through a greater angle than the outer.

AERODYNAMIC DRAG – Is the air resistance to the motion of the vehicle. This consists of profile drag, induced drag, skin friction drag, interference drag, and cooling and ventilation drag.

AERODYNAMIC LIFT – Is the vertical component of the resultant force caused by the pressure distribution on the vehicle body.

AIR BLEEDER – A device used to remove air from a hydraulic system. Types include a needle valve, capillary tubing to the reservoir, and a bleed plug.

AIR BRAKE – A braking system which uses compressed air to supply the effort required to apply brakes.

AIRFOIL – Device, similar to a stubby wing.

AIR RESISTANCE – The motion of an automobile is associated with the displacement of air particles, which requires some power of the engine. Air resistance depends on the size and shape of the vehicle body, speed of the vehicle and wind velocity.

AIR SPRING – Container and plunger are separated by air under pressure. When container and plunger attempt to squeeze together, air compresses and produces a spring effect. Air spring has been used in some suspension systems.

ALL WEATHER TYRE – A tyre designed to provide good traction on dry, wet and dirt and snow covered roadways.

ANTI DAZZLE MIRROR – One having a photoelectric control circuit which changes it from a fully reflecting condition to partial reflection from a glass air interface when actuated by the head lamp beam of a following vehicle.

ANTILOCK BRAKE SYSTEM (ABS) – If the brakes are applied so hard that the wheels tend to stop turning and thus a skid starts to develop, the antilock brake system comes into operation and partly releases the brakes. This makes the wheels continue to rotate. However, intermittent braking continues. But it is held below the point where the skid would start.

ANTIMIST PANEL – A panel fitted to the rear window enclosing a volume of still air between itself and the outer glass.

ANTIROLL BAR – Torsion bar mounted transversely in the chassis in such a way so as to counteract the effect of opposite spring deflections.

ARCH – The curve of a leaf spring. If the centre is lower than the ends, it is called positive arch, if the centre is higher than the ends, it is called negative arch.

ARCING (brakes) – Grinding new brake linings to the same diameter (arc) as that of the brake drum surface.

ASPECT RATIO – The ratio of the width to the length. On tyres, it is the fully inflated height divided by the cross section.

AUTOMOBILE – is a self propelled vehicle. The power required to propel the vehicle is supplied by the engine (also called prime mover). Scooters, motor cycles, cars, buses, trucks etc., are different types of automotive vehicles.

AUTOMATIC LEVEL CONTROL – A suspension system which compensates for variations in load in the rear of the car, positioning the rear at a pre-designed level regardless of load.

AUTOMATIC TRANSMISSION – A power transmission system for road vehicles, in which the approximately optimum engine speed is maintained through mechanical or hydraulic speed changing devices which are automatically selected and operated by reference to the road speed of the vehicle.

AXLE – A cross bar supporting a vehicle on which one or more wheels turn.

AXLE (full floating) – Axle used to drive rear wheels. It does not hold the wheels on nor support them.

AXLE (semi quarter or one quarter floating) – Axle used to drive wheels, hold them on and support them.

AXLE THREE QUARTER FLOATING – Axle used to drive rear wheels as well as hold them on and support them.

AXLE FLANGE – A flat surface on the outboard end of the axle shaft to allow wheel attachment.

AXLE GEAR – A gear in the differential carrier that drives the driving wheels.

AXLE RATIO – Relationship or ratio between the numbers of times the propeller shaft or drive shaft must revolve to turn the axle shafts one turn.

AXLE SHAFT – The shaft used to transmit power from the differential to the wheels.

BACK LOCKING – The steering gear is so constructed that it is easy to turn the vehicle by steering wheel, but it is difficult to turn the steering wheel by turning the front wheels. This back locking prevents the bumps and shocks experienced by the wheel on the road surface from being transmitted to the steering wheel.

BACKING PLATE – A mounting plate that holds the brake shoes, cam lever, pivot pins and springs inside the brake drum.

BALL JOINT – Flexible joint utilizing ball and socket type of construction, used in steering linkage set ups, steering knuckle pivot supports etc.

BALL JOINT ROCKER ARMS – Rocker arms that instead of being mounted on shaft, are mounted upon ball shaped devices on end of stud.

BALL JOINT STEERING KNUCKLE – Steering knuckle that pivots on ball joints instead on king pin.

BALL JOINT SUSPENSION – A type of front suspension, which does not use a steering knuckle. Instead, the wheel spindle is attached directly to the upper and lower suspension arms through ball joints. Allows movement up and down as well as rotation.

BALL STUD – Stud with a ball on end, commonly used in steering linkage to connect pitman arm to linkage, or to connect tie rods.

BALL AND TRUNNION JOINT – A type of universal joint which combines the universal joint and slip joint in one assembly.

BEAD (tyre) – Steel wire reinforced portion around a tyre opening that engages the wheel rim.

BELL HOUSING (clutch housing) – Metal (cast iron or aluminium) cover that surrounds flywheel and clutch, or torque converter assembly.

BELL MOUTH – The taper of a brake drum.

BELTED TYRE – A tyre that is reinforced with a build up of cord under the tread area.

BENCH BLEEDING – Process of removing air from the master cylinder pressure area before installing it in the vehicle.

BENDIX TYPE STARTER – A self engaging starter drive gear. Gear moves into engagement when starter armature shaft starts spinning and automatically disengages when starter stops and engine speed increases.

BIAS BELTED TYRE – A tyre in which plies are laid on the bias, criss crossing each other, with a circumferential belt on top of them. The rubber tread is vulcanized on top of the belt and plies.

BINDERS – Compounds that hold the friction materials together in brake linings.

BLEEDING – Removing air, pressure, fluid etc. from a closed system as in the brake system or air conditioning system.

BLEEDING (brakes) – Removal of air from hydraulic system. Bleeder screws are loosened at each wheel cylinder (one at a time) and brake fluid is forced from master cylinder through lines until all air is expelled.

BLEEDING (steering) – A process by which air is removed from a hydraulic system (power steering) by bleeding off part of the fluid or operating the system to work without the air.

BODY – The assembly of sheet metal sections together with windows, doors, seats and other parts, that provide an enclosure for the passengers, engine and so on.

BODY PANELS – Sheets or panels of steel which are fastened together by welding to form the vehicle body.

BODY ROLL – The vehicle body leaning sideways as the vehicle turns.

BOGIE – A small truck, of short wheel base running on rails, commonly used for the conveyance of coal, gold or other ores, concrete etc.

BONDED BRAKE LINING – Brake lining that is attached to the brake shoe by adhesive.

BONNET – British term for car hood.

BOOSTER – Device incorporated in a car system (such as brake and steering), to increase pressure output or decrease amount of effort required to operate or both.

BORG WARNER OVER DRIVE – A method of reducing engine rpm in relation to road speed. The unit is attached at the rear of the gear box and operates through epicyclic gears.

BRAKE – An energy conversion device that converts the energy of motion into heat energy and thereby slows down or stops a moving vehicle.

BRAKE (disc type) – Braking system which uses steel disc with calliper type lining application. When brakes are applied, section of lining on the calliper piston on each side of the spinning disc is forced against the disc thus imparting braking force. This type of brake is very resistance to brake fade. Also called disc brake system.

BRAKE ANCHOR – Steel stud upon which one end of brake shoes is either attached to or rests against. Anchor is firmly affixed to backing plate.

BRAKE ANTIROLL DEVICE – Unit installed in brake system to hold brake line pressure when car is stopped on upgrade, and brake pedal is released. Antiroll device will keep brakes applied until either clutch is released or, as in some models, accelerator is depressed.

BRAKE BACKING PLATE – Rigid steel plate upon which brake shoes are attached. Braking force applied to shoes is absorbed by backing plate.

BRAKE BAND – Band faced with brake lining, that encircles a brake drum. Used on several parking brake installations.

BRAKE BIAS – The stopping effort of the front wheels compared to that of the rear wheels.

BRAKE CALIPER – The hydraulic cylinder at the wheel used to apply the disc brake linings against the rotor.

BRAKE CLEARANCE – is the clearance provided between the lining and the drum or disc. Wear and tear of the lining increases this clearance and hence to be adjusted periodically.

BRAKE DRUM – Metal drum mounted to the vehicle wheel which forms  the outer shell of the brake. Brake shoes when moved out or moved apart press against the rotating drum to slow or stop drum and wheel rotation.

BRAKE EFFECTIVENESS – is how effectively the brakes perform their function. This depends on the area of the brake lining, amount of pressure applied to the brake shoes, radius of the brake drum, vehicle wheel radius, coefficient of friction of braking surfaces and coefficient of friction between the tyre and the road surface.

BRAKE FADE – A reduction or fading out of braking effectiveness due to loss of friction between brake shoes and drum. This is caused by overheating (heat build up) from excessively long and hard brake application for instance, when coming down a long hill or mountain.

BRAKE FEEL – The reaction of the brake pedal against the drivers foot, that tells him how heavily he is applying the brakes.

BRAKE FLUID – A special non -mineral oil fluid used in hydraulic braking system. Never use anything else in place of regular fluid.

BRAKE FLUSHING – Cleaning brake system by flushing with alcohol or brake fluid. Done to remove water, dirt or any other contaminant. Flushing fluid is placed in master cylinder and forced through lines and wheel cylinders where it exits at cylinder bleed screws.

BRAKE LINE – Special hydraulic tube made of steel, plastic or reinforced rubber suitably designed to withstand extreme pressure without deforming.

BRAKE LINING – A special high friction material made of asbestos and other materials bonded to brake shoes and brake pad plates. Brake lining produces friction and heat when it is forced against the brake drum or disc.

BRAKE PULL – A condition in which the vehicle turns each time the brakes are applied.

BRAKE ROTOR – The brake friction surface that rotates at wheel speed designed for contact with the brake pads on disc brake assemblies.

BRAKE SELF ADJUSTERS – A cable operated device used to adjust brake shoes automatically.

BRAKE SHOES (disc brakes) – Flat metal pieces lined with brake lining which are forced against the rotor face. Also called brake pads.

BRAKE SHOES (drum brakes) – Arc shaped metal pieces lined with heat resistant fibre. When forced against the brake drum, stops wheel rotation.

BRAKE SHOE HEEL – End of brake shoe adjacent to anchor bolt or pin.

BRAKE SHOE TOE – Free end of brake shoe, not attached to or resting against an anchor pin.

BRAKING SYSTEM EFFICIENCY – is measured in terms of the rate at which brake will bring the vehicle to a stationary position from a given speed. It is expressed as the ratio of the vehicle deceleration rate to the acceleration due to gravity.

BREAKE (tyre) – Rubber or fabric (or both) strip placed under the tread to provide additional protection for main tyre carcass.

BULK HEAD – The structural part of the vehicle connecting the front of the floor assembly to the roof structure.

BUMPER – which is attached to the vehicle frame takes the shock of impact or collision and transfer the same to the frame. By this means, damage to engine parts, radiator, lamps etc. is avoided.

BUMP STEER – The steering effect caused by the suspension moving through its travel.

CALIPER – A housing for the hydraulic components of a disc brake system.

CAMBER – Tilting of the top of wheels from the vertical, when the tilt is outward, camber is positive.

CAMBER ANGLE – The outward (positive) or inward (negative) angle of the wheel centre line to absolute vertical.

CARDAN UNIVERSAL JOINT – A universal joint of the ball and socket type.

CARLIFT – An air, electrical or hydraulically operated piece of shop equipment which can lift the entire vehicle, or in some cases, one end of the vehicle.

CARRIER BEARINGS – Bearings upon which differential case is mounted.

CASING OF TYRE – The tyre casing, made of fabric or cord to which rubber is vulcanized. It is the outer part of the tyre assembly.

CASTER – The tendency of a wheel to follow the direction of the pivot movement. Tilt of the top of the king pin forward or backward from the vertical. When tipped forward it is called negative caster. Backward tilt from the vertical is called positive caster.

CASTER ANGLE – The rearward (positive) or forward (negative) angle of the steering axis to absolute vertical.

CENTRE STEERING LINKAGE – Steering system utilizing two tie rods connected to steering arms and to central idler arm. Idler arm is operated by drag link that connects idler arm to pitman arm.

CENTRIFUGAL CLUTCH – Clutch that utilizes centrifugal force to expand a friction device on driving shaft until it is locked to a drum on driven shaft. The clutch comes into action as it spins faster.

CHANNELED – Car body lowered down around frame.

CHASSIS – Generally chassis refers to the unit that consists of frame, engine, front and rear axles, springs, steering and brake systems, controls, drive train and fuel tank. It is an assembly of mechanisms that make up the major operating part of the vehicle. In short, it is assumed to include everything except the vehicle body and fenders.

CLASSIC or NORMAL CONTROL TRUCK – has the engine located in front of the driver’s cabin.

CLUTCH – Device used to connect or disconnect flow of power from one unit to another. In a vehicle, the mechanism in the power train that connects the engine crankshaft to or disconnects it from the transmission and thus with the remainder of the power train.

CLUTCH CHATTER – A shaking or shuddering of the vehicle as the clutch is operated.

CLUTCH DIAPHRAGM SPRING – Round dish shaped piece of flat spring steel, used to force pressure plate against clutch disc in some clutches.

CLUTCH DISC – Part of the clutch assembly splined to transmission clutch or input shaft, faced with friction material. When clutch is engaged, disc is squeezed between flywheel and clutch pressure plate.

CLUTCH DRAG – A problem in which the clutch disc does not come to a complete stop after the clutch pedal is depressed.

CLUTCH EXPLOSION – Clutches have literally flown apart (exploded) when subjected to high rotational speed. Scatter shield is used on competition cars to protect driver and spectators from flying parts in event clutch explodes.

CLUTCH HOUSING – A metal housing that surrounds the flywheel and clutch assembly.

CLUTCH LINKAGE – The rods and levers that allow the driver to operate the clutch.

CLUTCH PEDAL – A pedal in the driver’s compartment that operates the clutch.

CLUTCH PEDAL FREE TRAVEL – Specified distance clutch pedal may be depressed before throw out bearing actually contacts clutch release fingers.

CLUTCH PILOT BEARING – A small bronze bushing or ball bearing positioned in the crankshaft end or centre of flywheel, used to support outboard end of transmission input shaft.

CLUTCH PRESSURE PLATE – Part of a clutch assembly, that through spring pressure, squeezes clutch disc against flywheel thereby transmitting driving force through the assembly. To disengage clutch, pressure plate is drawn away from the flywheel via linkages.

CLUTCH SEMI CENTRIFUGAL RELEASE FINGERS – Clutch release fingers that have a weight attached to them, so that at high rpm release fingers place additional pressure on clutch pressure plate.

CLUTCH SHAFT – The shaft on which the clutch is assembled, with the gear that drives the countershaft in the transmission on one end. It has external splines that can be used by a synchronizer drum to lock the clutch shaft to the main shaft for direct drive.

CLUTCH SLIPPAGE – A condition in which the engine over revs during shifting or acceleration.

CLUTCH THROWOUT FORK – In the clutch, a Y shaped member into which is assembled the throw out bearing.

CLUSTER or COUNTER GEAR – Cluster of gears that are all cut on one long gear blank. Cluster gears ride in the bottom of transmission. Cluster provides a connection between transmission input shaft and output shaft.

COEFFICIENT OF FRICTION – An index of the frictional characteristics of a material.

COEFFICIENT OF ROLLING RESISTANCE – is numerically equal to the ratio of the force causing uniform rolling of the wheel to the normal reaction of the road.

COIL SPRING CLUTCH – A clutch using coil springs to hold the pressure plate against the friction disc.

COLLAPSIBLE STEERING COLUMN – is the steering column which will collapse in its length due to the impact of the driver on to the steering wheel, on a front end crash. This safety device prevents the possibility of the driver getting injured.

CONE CLUTCH – Clutch utilizing cone shaped member that is forced into a cone shaped depression in the flywheel, or the other driving unit. Although no longer used in cars, cone clutch finds some applications in small riding tractors, heavy power movers etc.

CONSTANT VELOCITY JOINT – Two closely coupled universal joints arranged so that their acceleration and deceleration effects cancel out each other, resulting in an output driven shaft speed to be always identical with drive shaft speed.

CONTACT PATCH – The part of a tyre that is in contact with the road surface.

CONTROL ARM – A suspension member mounted horizontally with one end attached to the frame and the other end the knuckle or axle housing.

CORD – A string or thread that makes up the fabric used in tyre plays.

CORNERING WEAR – A type of tyre tread wear caused by taking turns at excessive speeds.

COUNTERSHAFT – Intermediate shaft that receives motion from one shaft and transmits it to another. It may be fixed (gears turn on it) or it may be free to rotate. In the transmission countershaft is driven by the clutch gear, gears on the countershaft drive gears on the main shaft when the latter are shifted into gear.

COWL – Part of car body between engine firewall and front of dashboard.

CROSS SHAFT (steering) – Shaft in steering box that engages steering shaft worm. Cross shaft is splined to pitman arm.

CURB WEIGHT – The weight of the complete vehicle with its normal load, less driver and passengers but with a full tank of fuel, engine and vehicle oil and coolant.

CUT OUT – operates as an automatic switch which connects and disconnects the battery with the generator, according to the speed of the latter.

DAMPERS – are nothing but a piston in a cylinder filled with oil or gas. The damper restrains undesirable bounce of the sprung vehicle mass and restrains the wheel assembly from loosing ground contact by being excited at its natural frequency.

DASH BOARD – Part of body containing driving and control instruments, switches etc.

DEAD AXLE – Axle that does not rotate or deliver power but merely forms a base upon which wheels may be mounted.

DEDION – Rear axle set up in which driving wheels are attached to the frame by a central pivot. Differential unit is bolted to frame and is connected to the driving wheels by drive axles.

DEPENDENT SUSPENSION – Wheel connected through an axle member so that movement of one wheel moves the other wheel.

DIAGONAL SPLIT BRAKE SYSTEM – A brake system design that will allow application of brakes on one front wheel and a diagonally opposite rear wheel, when part of brake system fails.

DIAPHRAGM CLUTCH – Uses a diaphragm or conical spring instead of coil springs to produce adequate pressure required for keeping the clutch in the engaged position.

DIFFERENTIAL – A mechanism between axles that permit one wheel to turn at a different speed than the other while transmitting power from the drive shaft to the wheel axles, when the vehicle is negotiating a turn.

DIFFERENTIAL CASE – A steel unit to which the ring gear is attached. Differential case drives spider gears and forms an inner boring surface for axle and gears.

DIFFERENTIAL LOCK – The differential lock grips one or both of the side gears to the differential case. This prevents their rotation on the pins. This enables a larger torque to be transmitted to the gripping wheel than that to the slipping wheel.

DIRECT ACTING SHOCK ABSORBER – Type of shock absorber which shortens or lengthens in action. Also called telescopic shock absorber.

DIRECT DRIVE – Such as high gear when crankshaft and drive shaft revolve at same speed.

DIRECTIONAL STABILITY (steering) – Ability of vehicle to move forward in straight line with minimum of driver control. Vehicle with good directional stability will not be unduly affected by side wind, road irregularities etc.

DISC BRAKE – When the brake pedal is depressed, pads lined with friction material are forced towards one another. In doing so, they come in contact with the disc (attached to the wheel) which normally rotates between them. This provides braking effort.

DISC WHEEL – Wheel constructed of stamped sheet.

DIVE – The front wheel of the vehicle lowering during braking.

DOLLY BLOCKS – Blocks of metal, variously shaped and contoured, used to straighten body panels and fenders. The dolly block is held on one side of the panel while the other side is struck with a special hammer.

DOUBLE LEADING SHOE – A drum brake having two leading shoes and no trailing shoes. Each shoe has its own actuating mechanism and pivot.

DOUBLE PISTON CALIPER – A hydraulic brake calliper with two pistons and provision for applying hydraulic pressure equally to both pistons. The calliper body is fixed solidly.

DOWN SHIFT – Shifting to lower gear.

DOUBLE LEADING BRAKE – A drum brake assembly with both front shoes self energized during forward wheel rotation.

DOUBLE REDUCTION AXLE – In the double reduction or triple reduction type final drive, the required speed reduction is obtained in two or more steps. This enables higher torque to be available at the road wheels. In heavy duty and off highway vehicles, multiple reduction is used.

DOUBLE TRAILING BRAKE – A drum brake assembly with both shoes self energized during rearward wheel rotation only.

DRAG – To accelerate a vehicle from standing start, over course one fourth mile in length. Also used by some drivers when referring to challenging another driver to an acceleration race.

DRAG LINK – A steel rod connecting pitman arm to one of steering knuckles. On some installations, drag link connects pitman arm to a centre idler arm.

DRAGSTER – Car especially built for drag racing.

DRAG WHEEL – Special steering wheel used on some dragsters. Often consists of cross bar spoke and portion of rim on each end.

DRIP MOULDING – is a U shaped channel, added to the side rails of the roof panel. It catches water on the roof and direct it to the back of the car during raining.

DRIVE LINE or DRIVE TRAIN – Propeller shaft, universal joints etc. connecting transmission output shaft to axle pinion gear shaft.

DRIVE PINION – A gear in the differential connected to the drive shaft.

DRIVE or PROPELLER SHAFT SAFETY STRAP – A metal strap or straps, surrounding drive shaft to prevent shaft from falling to ground in the event of a universal joint or shaft failure.

DRIVE SHAFT – An assembly of one or two universal joints connected to a hollow tube and used to transmit torque and motion. A shaft in the power train that extends from the transmission to the differential and transmits power from one to the other. Also called PROPELLER SHAFT.

DROP CENTRE RIM – Centre section of rim being lower than two outer edges. This allows bead of tyre to be pushed into lower area on one side while the other side is pulled over and off the flange.

DROPPED AXLE – Front axle altered so as to lower the frame of the vehicle. Consists of bending axle downward at outer ends (solid front axle).

DRUM BRAKE – A brake unit using curved brake shoes which press against the inner circumference of a metal drum to produce braking action.

DUALS – Two sets of exhaust pipes and mufflers one for each bank of cylinders.

DUAL BRAKE SYSTEM – Tandem or dual master cylinder to provide a brake system that has two separate hydraulic systems, one operating the front brakes, the other operating the rear brakes.

DUAL SERVO BRAKES – A drum brake assembly with both front and rear shoes, self energized during forward and rearward wheel rotations.

DUMMY AXLE – provided in some vehicles increases the load carrying capacity of the vehicle. Wheels on the dummy axle can rotate freely.

DUNY BUGGY – Off road vehicle set up to run on sand.

ELLIOT TYPE AXLE – Solid bar front axle on which ends span or straddle steering knuckle.

EMERGENCY BRAKE – is the hand brake, operated by a lever, is used when the vehicle is left parked and prevents the vehicle from moving. The hand brake can be applied to stop the vehicle when the service brake fails.

EPICYCLIC GEAR – In the epicyclic gearing, at least one gear not only rotates about its own axis, but also rotates about some other axis.

EQUALIZER LINK – A common connector in the parking brake system that causes both rear brakes to be applied with the same cable tension.

EVASIVE MANEUVER – Rapid steering changes to avoid obstacles in the path of the vehicle.

EXPANSION TANK – A tank at the top of an automobile radiator which provides room for heated coolant to expand and give off any air that may be trapped in the coolant. Also used in some fuel tanks to prevent fuel from spilling from the tank because of expansion.

FADE (brake) – A condition that occurs when there is little braking effect with full brake pedal force.

FIFTH WHEEL – is the swivelling type arrangement at the rear of a tractor unit. The fifth wheel carries the front part of the semitrailer.

FINAL DRIVE – The final gear reduction between the engine and the drive wheels.

FIXED CALIPER DISC BRAKES – Disc brakes using a calliper which is

fixed in position and cannot move.

FLOATING CALIPER DISC BRAKES – Disc brakes using a calliper mounted through rubber bushings which permit the calliper to float, or move, when the brakes are applied.

FLUID FLY WHEEL – A liquid coupling used to transmit the engine effort (torque) to a clutch and transmission. This coupling is always a major part of the engine flywheel.

FOOT PRINT – Area of road that is in contact with the tyre.

FORWARD CONTROL TRUCK – has the engine either in or below the driver’s cabin.

FORWARD EFFICIENCY – is the ratio of the amount of driver input torque which is available at the wheels to turn the same to the total amount of input torque from the driver at the steering wheel.

FOUR WHEEL DRIVE – Some cross country vehicles (Jeeps) have this arrangement. In this case, the engine power is transmitted to all the four wheels of the vehicle. The main advantage of this arrangement is the entire vehicle weight is available for traction.

FOUR WHEEL STEERING – Type of steering system in which all the four wheels of a vehicle are turned for steering.

FOUR SPEED TRANSMISSION – A transmission with four forward speeds or gear ratios.

FRAME – The assembly of metal structural parts and channel sections that forms the base and supports the engine and body and is supported by the vehicle wheels.

FRONT AXLE – In a vehicle, the front axle transmits the weight of the front part of the vehicle to the road surface through the front wheels. It also carries the mechanism for steering the vehicle. In the case of front wheel drive, it incorporates both steering and driving mechanisms.

FRONT END GEOMETRY – The angular relationship between the front wheels, wheel attaching parts, and vehicle frame. Includes camber, caster, king pin inclination, toe in and toe out on turns.

FULL FLOATING AXLE – An axle design usually used on heavy trucks where the vehicle weight is carried by bearings in the wheel hubs, or the drive wheels and the axles are used only to transfer driving torque.

GEAR – A wheel with teeth that engage or mesh with teeth of another wheel.

GEAR BOX – A unit which has a series of gears and shafts to vary the speed of the gearbox output shaft compared to the engine speed. This in turn increases the torque and thereby improves acceleration of the vehicle.

GEAR CLASH – A condition in which the gears grind during shifting.

GEAR RATIO – The ratio of the number of teeth on two gears to mesh with each other.

GENERATOR – is the device which converts mechanical energy from the automobile engine into electrical energy. When the generator is sufficiently turned by the engine, it furnishes electrical energy for all the vehicles circuits and replenishes the battery to keep it fully charged.

GRAVITY BLEEDING – A process used to remove air from the brake system using the natural height of the fluid in the master cylinder above the wheel cylinder.

GRIP COEFFICIENT – is numerically equal to the ratio of the force causing uniform wheel slip to the normal road resistance.

HALF AXLE DRIVE SHAFTS – Two in number, transmit the driving torque from the final drive and differential unit to the driving road wheels.

HANDLING – The ease of manoeuvring a vehicle without slipping or skidding.

HARSHNESS – Bumpy ride produced by a stiff suspension.

HEEL – Anchor end of a brake shoe.

HOTCHKISS DRIVE – A rear suspension with open propeller shafts with two or three universal joints. Braking torques are transferred to the frame through links, control arms or leaf springs.

HORN RELAY – A relay connected between the battery and horns, when energized by closing of the horn button, it connects the horn to the battery.

HYDRAULIC BRAKE – A brake system using hydraulic fluid, piston and cylinders to provide extremely high pressure for break application.

HYDRAULIC CLUTCH – A clutch that uses hydraulic pressure to actuate the clutch. Used in heavy duty equipment and where the engine is away from the driver’s compartment so that it would be difficult to use mechanical linkages.

HYDRAULIC CONTROL VALVES – A system of valves that senses driving conditions and automatically shifts the transmission.

HYPOID GEARS – Drive pinion and ring gears whose shape allows them to mesh off centre.

IMPENDING SKID – The tyre traction point at which any increase in side or tractive load will produce tyre skid.

INDEPENDENT SUSPENSION – A type of suspension system in which each wheel is independently supported by a spring. A suspension that allows up and down movement of one wheel without affecting the opposite wheel.

INNER TUBE (tyre) – The inside rubber tube assembled in the tyre casing, it maintains the air at sufficient pressure to inflate the casing and adequately support the vehicle weight.

INTEGRAL BODY – has the longitudinal and cross members of the chassis incorporated in the frame work of the load carrying body. With this arrangement, part of the load previously carried by the chassis, is diffused through the body structure.

ISOFLARE – A brake tube flaring method that upsets the tube and allows a strong, secure attachment when used with the proper tube nut and seal.

JOUNCE – A compression load on the springs as the space between the frame and the axle is reduced.

JOUNCE BUMPER – A rubber bumper used to absorb shock during full suspension system movement.

KING PIN – The steel pin on which the steering knuckle pivots, it attaches the steering knuckle to the knuckle support or axle.

KING PIN INCLINATION – Inward tilt of the king pin from the vertical.

KINGPIN OFFSET – is the distance between the centre of the tyre contact patch and intersection of the kingpin or steering axis with the ground. Kingpin offset is also called scrub radius.

KNOCK BACK – Slight axial movement that pushes the calliper pistons into their bore. This causes clearance between the brake lining and the rotor.

KNUCKLE – The part of the suspension that connects the control arms and supports the wheel spindle.

LATERAL LOAD (tyre) – The force on the side of the tyre treads.

LEADING SHOE – A brake shoe that has the drum rotating from the toe toward heel.

LEADING TRAILING BRAKE – A drum brake assembly having one shoe energized in either forward or rearward wheel rotation.

LEAF SPRING – A spring made up of a series of flat steel plates of graduated length, assembled one on top of another.

LEVEL CONTROL (automatic) – A suspension system which compensates for variations in load in the rear of the car, positioning the rear at a predesigned level regardless of load.

LIMITED SLIP DIFFERENTIAL – A differential allowing unequal torques to be delivered to the axle shafts.

LINKAGE POWER STEERING – A type of power steering in which the power steering units (power cylinder and valve) are an integral part of the steering linkage.

LORD LEVELING SYSTEM – A system used to level a vehicle that is heavily loaded.

LORD RANGE (tyre) – The amount of weight that can be safely carried by a tyre. It indicates the number of plies at which a tyre is rated. Load range B equals 4 ply rating, C equals 6 ply rating, and D equals 8 ply rating.

LUG – The flange stud on an axle or hub on which the drum and wheel are fastened.

MCPHERSON STRUT SUSPENSION – A suspension system in which both wheels are attached to a rigid rear axle housing.

MANUALLY OPERATED TRANSMISSION – A transmission that is shifted from one speed to another by the operator (driver).

MASTER CYLINDER – The liquid filled cylinder in the hydraulic braking system where hydraulic pressure is developed by depression of the brake pedal or movement of the brake lever.

MECHANICAL BRAKES – Brakes operated by mechanical linkage (cables and levers) between the brake pedal and the brakes at the car wheels.

METALLIC BRAKE LINING – A lining having metallic properties used to provide high temperature braking efficiency.

METERING VALVE – A valve that delays pressure build up to the front brakes of a four wheeled vehicle.

MINOR BRAKE ADJUSTMENT – Adjustment of brakes to compensate for brake lining wear.

MODULATOR – A vacuum canister mounted to the outside of the automatic transmission that senses engine load.

MULTIPLE DISC CLUTCH – A clutch that has more than one friction disc, usually there are several driving discs and several driven discs, alternately placed.

NEUTRAL STEER – A vehicle that will maintain the selected turn with no driver input.

NON DIRECTIONAL SENSE – Steering does not lead in any direction.

NON LOAD CARRYING BODY – In this, the loads on the vehicle are transferred to the suspension system entirely by a separate chassis. The body is isolated from the chassis deflection by rubber mountings.

ONE WAY CLUTCH – A clutch that holds in one direction but allows movement in another direction.

OVER DRIVE – A device in the power train of some vehicles that introduces an extra set of gears into the power train. This causes the propeller shaft to overdrive or drive faster than the engine crankshaft. Engine speed is thus reduced without reduction of vehicle speed.

OVER RUNNING CLUTCH – A type of clutch that will transmit rotary motion in one direction only, when rotary motion attempts to pass through in other direction, then the driving member over runs and does not pass motion to the other member.

OVER STEER – The tendency of a vehicle to turn sharper than the turn selected by the driver.

PANHARD ROD – A control rod that connects the frame on one side of the vehicle to the axle housing on the other side to keep the axle housing centred under the vehicle.

PARKING BRAKES – Mechanically operated brakes that operate independently of the (hydraulic) service brakes on the vehicle. They may be set for parking the vehicle or holding the vehicle against rolling. Also called an emergency brake.

PASCAL’S LAW – A principle of hydraulics which states that pressure at any point in a confined liquid is same in every direction and applies equal force on equal areas.

PEDAL BLEEDING – A method of removing air from the hydraulic system parts by applying the brake to raise the pressure in the system to help move the air through the system when the bleeder valves are opened.

PEDAL PULSATION – A rapid up and down movement of the clutch pedal during operation.

PITMAN ARM – That part of the steering gear which is linked to the steering knuckle arms of the wheels; it swings back and forth for steering.

PITMAN ARM STOPS – On some cars (particularly those using linkage power steering), stops are used to prevent excessive pitman arm movement and thus steering linkage movement.

PITMAN SHAFT – The shaft to which the pitman arm is attached in a steering gear.

PLANETARY GEARBOX – A system of gears used in an automatic transmission, a sun gear, planet gears, a carrier and a ring gear.

PLIES – The layers of cord fabric in a tyre carcass, each layer is a ply.

PLYSTEER – The tendency of a tyre to always turn in one direction as it rolls. This is the result of the way the tyre was constructed.

PNEUMATIC TYRES – Tyres that are filled with air to the required pressure.

POWER BOOSTER – A device used to increase the drivers brake pedal force going to the master cylinder, without an accompanying increase in pedal travel.

POWER BRAKE – Conventional brake system that utilizes engine vacuum to operate vacuum power piston. Power piston applies pressure to brake pedal, or in some cases, directly to master cylinder piston. This reduces the amount of pedal pressure that the driver must exert to stop the vehicle. Also called POWER ASSISTED BRAKE.

POWER RACK – In the saginan power steering unit, a rack that meshes with a sector on the pitman shaft and transmits to the shaft, power from the power cylinder.

POWER STEERING – A device that uses hydraulic pressure to multiply the drivers effort as he turns the steering wheel so that less steering effort is required.

POWER TRAIN or DRIVE TRAIN – The group of mechanisms that carry the rotary motion developed in the engine to the vehicle wheels, it includes the clutch, transmission, drive shaft differential and axles.

PRESSURE CAP (radiator) – A radiator cap with valves that causes the cooling system to operate under pressure and thus at a somewhat higher and more efficient temperature.

PRESSURE PLATE – That part of the clutch which exerts pressure against the friction disc, it is mounted on and rotates with the flywheel.

PREVENTIVE MAINTENANCE – The systematic inspection, detection and correction of failures in a engine, or in a vehicle, either before they occur, or before they develop into major defects.

PRIMARY SHOE – A brake shoe moved by a wheel cylinder to apply the brake.

PROPELLER SHAFT – A shaft in the power train that extends from the transmission to the differential and transmits power from one to the other.

PROPORTIONING VALVE – A valve used to maintain the correct proportion of fluid pressure between the front disc or drum brakes and rear drum brakes. Usually the rear brake pressure is a fraction of front brake pressure.

PUNCTURE SEALING TYRES AND TUBES – Tyres and tubes coated on the inside with a plastic material. Air pressure in the tyre or tube forces that material through holes made by punctures. It hardens on contact with the air to seal the puncture.

RACK AND PINION STEERING GEAR – A steering gear that uses a pinion on the end of the steering shaft which is meshed with a rack on the major cross member of the steering linkage.

RADIAL BIAS TYRE – A tyre in which the plies are laid on radially, or perpendicular to the rim, with a circumferential belt on top of them. The rubber tread is vulcanized on top of the belt and plies.

RADIAL PLY TYRE – Cords running directly across the tyre carcass from bead to bead.

RADIAL SPRING RATE – The amount of radial load required to deflect a tyre (one cm) unit distance.

RADIATOR – In the cooling system, the device that removes heat from the coolant passing through it, it takes hot coolant from the engine and returns the coolant to the engine at a lower temperature. The hot coolant is cooled in the radiator for recirculation.

RADIATOR PRESSURE CAP – The cap placed on the radiator filler tube which pressurizes the cooling system for more efficient operation.

RADIATOR SHUTTER SYSTEM – A system of engine temperature control used mostly on trucks, that controls the amount of air flowing through the radiator by use of a shutter system.

REACTION CONTROL – A feedback mechanism that gives the driver a feel of the amount of input effort being applied.

REAR AXLE ASSEMBLY – A system of gears and axles that transfers power from the drive line assembly to the driving wheels of the automobile.

REAR AXLE RATIO – The ratio between the drive pinion and the ring gear in the differential assembly.

REAR END TORQUE – Reactionary torque applied to the rear axle housing as torque is applied to the wheels; rear end torque attempts to turn the axle housing in a direction opposite to wheel rotation.

REBOUND – An expansion of a suspension spring after it has been compressed as the result of jounce.

RECAPPING – A form of tyre repair in which a cap of new materials is placed on the old tread and vulcanized into place.

RECIRCULATING BALL AND NUT STEERING GEAR – A type of steering gear in which there is a nut (meshing with a gear sector) assembled on a worm, balls circulate between the nut and worm threads.

RELEASE LEVER – In the clutch, a lever that is moved by throw out bearing movement; the movement causes clutch spring pressure to be relieved so that the clutch is released or uncoupled.

RETREAD – A used tyre on which a new tread section is molded.

REVERSE FLUSHING – A method of cleaning a radiator or engine cooling system by flushing in the direction opposite to the normal coolant flow.

RIDE – The characteristic feel as one rides in a vehicle.

RIGID REAR SUSPENSION – A rear suspension system in which both wheels are attached to rigid rear axle housing.

RIM – The metal wheel on which the tyre is mounted.

RING GEAR – A large gear carried by the differential case, meshed with and driven by the drive pinion.

ROAD RESISTANCE – is the resistance of the road surface, which must be overcome when a vehicle travels along the road. This consists of friction between the tyre and road.

ROLLING RESISTANCE – is the resistance caused due to the deformation of the tyres and road, the friction of the tyres on the road surface and friction in the wheel bearings.

ROLL STEER – The steering effect as a result of body lean during a turn.

RUNOUT OF WHEEL – Lack of alignment of wheel or gear to the axle so that the wheel or gear runout or move out of alignment, as wheel or gear rotates.

SAFETY RIM – A type of wheel rim having a hump on the inner edge of the ledge on which the tyre bead rides. The hump helps hold the tyre on the rim in case of blow out.

SCRUB RADIALS – The distance on the road surface under the front tyre between an extension of the pivot axis and the centre of weight.

SCUFF – The tyre slide on the road surface during operation.

SCUFF TRAVEL – The amount of side travel of the tyre as the wheel moves from maximum jounce to maximum rebound.

SEAT ADJUSTER – A device to permit forward and backward (and sometimes upward and downward) movement of the front seat.

SECONDARY SHOE – A brake shoe that is operated by a primary shoe to apply brake.

SELF ADJUSTING BRAKE DESIGNS – Brakes that automatically compensate for wear of the brake linings.

SELF ALIGNING TORQUE – The natural tendency of the tyre to return to the neutral position after being turned.

SEMIMETALLIC BRAKE LINING – A brake lining combining both metallic and organic materials for improved braking performance.

SENSTRONIC BRAKE – CONTROL (SBC) – is basically a brake by wire system which eliminates the need for mechanical linkage between the brake pedal and brake master cylinder.

SEQUENTIAL GEAR BOX – is an electromechanical device that replaces the conventional gear shift mechanism and is bolted to the tunnel section or the floor of the car. It converts the conventional floor shifter to an electronically activated sequential shift system that is electronically controlled by microprocessors.

SERIES – The designation of a tyre aspect ratio.

SERVICE BRAKE SYSTEM– The main braking system of the vehicle which controls braking effect proportional to the drivers demand.

SHACKLE – Swinging support by which one end of a leaf spring is attached to the vehicle frame.

SHIM – A slotted strip of metal used as a spacer to adjust front end alignment on many cars and to make small correction in the position of the body sheet metal and other parts.

SHIMMY – Rapid oscillations, in wheel shimmy, for example, the front wheel tries to turn in and out alternately and rapidly (a violent front wheel shake). This causes the front end of the car to oscillate or shimmy.

SHOCK ABSORBER – The assembly on the vehicle that checks excessively rapid spring movement and oscillations. A device placed at each vehicle wheel to regulate spring rebound and compression.

SHOE – The part of a brake that supports the lining.

SHORT LONG ARM SUSPENSION – A suspension system in which a long and a short control arms are used to support the wheel.

SINGLE LEADING SHOE – A drum brake having two shoes; one is leading another is trailing. Leading shoe tends to wedge itself into the brake drum and provides more braking action than the trailing shoe.

SINGLE REDUCTION AXLE – In the single reduction type final drive, the required speed reduction (say up to 7 to 1) is obtained in one step.

SIPES – Slits in the tyre tread to produce more blade surface for traction.

SKID – A tyre sliding on the road surface.

SKID CONTROL – A device that operates to prevent wheel lock up during braking and thus skidding.

SLIDING MESH GEAR BOX – The gear box consists of three shafts and a set of gears, gear selector mechanism and gear shift lever. Different gears are engaged by sliding the appropriate gears.

SLIP ANGLE – The angle between the tyre and the actual directional movement.

SLIP JOINT – In the power train, a variable length connection that permits the drive shaft (propeller shaft) to change its effective length.

SOCIETY OF AUTOMOTIVE ENGINEERS (SAE) – A professional engineering society responsible for setting many vehicle standards used in the world today.

SPIN BALANCER – A car tyre balancer which turns the raised tyre at a road speed where imbalance can be detected by wheel shake.

SPINDLE (steering system) – A part of the steering knuckle assembly on which the front wheels are mounted.

SPONGY PEDAL – A brake pedal that feels soft or spongy.

SPRING FREQUENCY – Springs are also compared in frequency. Springs which return quickly to their original shape or oscillate rapidly after being deflected are said to have higher frequency than those that return or oscillate slowly.

SPRING RATE – The flexibility of a spring depends on the property called spring rate. It is defined as the weight in kg required to deflect it one cm. A soft spring has a lower rate than a stiff or inflexible spring.

SPRING SHACKLE – Provides a means for the leaf spring assembly to compensate for changes in its length.

SPRING SUSPENSION – The operating components of a spring suspension system, which absorbs the force of road shocks by flexing and twisting.

SPRUNG WEIGHT – That part of the vehicle which is supported on springs (the frame and body for example).

SQUIRM – The twist of the tyre tread in the foot print.

STABILIZER SHAFT – An interconnecting torsion bar between left and right lower suspension arms on a vehicle which reduces body roll on turns and adds stability.

STAR WHEEL – An adjustable link between the primary and secondary brake shoes.

STEER ANGLE – The angle the wheels are turned to from straight ahead.

STEERING AND IGNITION LOCK – A locking device that locks the ignition switch in the off position, and also locks the steering wheel so that it cannot be turned.

STEERING ARM – The arm attached to the steering knuckle to turn the knuckle, and wheel, for steering.

STEERING AXIS – The centre line of the ball joints in a front suspension system extended to the road surface.

STEERING AXIS INCLINATION – The inward tilt of the steering axis or front wheel pivot from the vertical.

STEERING COLUMN – The housing that supports the steering shaft.

STEERING GEAR – That part of the steering system, located at the lower end of the steering shaft that carries the rotary motion of the steering wheel to the vehicle wheels for steering.

STEERING KICKBACK – Sharp rapid movements of steering wheel as the front wheels encounter obstructions in road, the shocks of these encounters kickback to the steering wheel.

STEERING KNUCKLE – The front wheel spindle or stub axle which is supported by the king pin, so that it and the wheel can be turned for steering. Part of the front suspension system.

STEERING LINKAGE – Linkage that connects the steering gears to the front wheels.

STEERING RATIO – The number of degrees the steering wheel is turned divided by the number of degrees the vehicle wheels are turned.

STEERING SHAFT – Shaft extending from steering gear to the steering wheel.

STEERING STOPS – limit the angular deflections of the front wheels. They avoid rubbing of tyres against the frame or against the fenders which would cause undue wear and tear of the tyres.

STEERING SYSTEM – The mechanism that enables the driver to turn the wheel axles (usually the front) and thus turn the wheels away from the straight ahead position so that the vehicle can be guided.

STEERING WHEEL – The wheel at the top of the steering shaft in the drivers compartment which is used to guide or steer, the vehicle.

STONE SHIELD – is bolted to the radiator support and the fenders. It fits beneath the bumper of the car. It prevents striking of small flying stones on to the radiator grille and radiator and thus avoids their damage.

STOP LIGHT SWITCH – A switch applied by the master cylinder pressure that turns on brake lights.

STOPPING DISTANCE – is the distance in which a vehicle will be brought to rest from steady speed, when the brake is applied.

STREAMLINING – The shaping of an object that moves through a medium (such as air or water) or past which the medium moves, so that less energy is lost by parting and reuniting of the medium as the object moves through it.

STUMBLE – The term related to vehicle driveability, the tendency of an engine to falter and then catch, resulting in a noticeable stumble effect felt by the driver.

SUSPENSION – The suspension system supports the vehicle body and at the same time isolates the vehicle and its occupants from shocks and vibrations generated by the road surface. It also maintains steering control and stability at all times.

SUSPENSION ARM – In the front suspension, one of the arms is pivoted at one end to the frame and at the other to the wheel (steering knuckle) support.

SUSPENSION COMPLIANCE – Rearward and upward movement of the suspension when the tyre meets an obstacle on the road surface.

SUSPENSION GEOMETRY – The angular action of the suspension as it goes from its static position to the extremes of travel (compared to vertical lines).

SYNCHROMESH – A device in the transmission that synchronizes gears about to be meshed so that there will not be any gear clash. Also called SYCHRONIZER.

TACTILE SENSOR – A sensor that allows the vehicle operator to feel when a certain condition is reached. Disc brake pads are made to vibrate when worn to the point where replacement is necessary and this vibration is felt in the brake pedal.

TANDEM MASTER CYLINDER – is the unit installed in some large cars and commercial vehicles have a split hydraulic system with two separate cylinders and reservoirs in the master cylinder. This avoids the possibility of complete brake failure due to a fracture in the pipe line leading to one brake cylinder.

THROWOUT BEARING – Bearing operated by the clutch linkage used to disengage the clutch.

TIE RODS – In the steering system, the rods that link the pitman arm to the steering knuckle arms.

TILT STEERING WHEEL – A type of steering wheel which can be tilted at various angles, due to a flex joint in the steering shaft.

TOE – The leading edge of the brake shoe. The angle between the centre lines of the front wheels.

TOE IN – The turning in of the front wheels, wheels are closer together at the front than at the back of the wheels.

TOE OUT – The turning out of the front wheels, where wheels are farther apart at the front than at the back of the wheels.

TOE OUT DURING TURNS – Difference in angles between the two front wheels and the car during turns. Inner wheel, in a turn, turns out or toes out more. Also called steering geometry and cornering wheel relationship.

TORQUE CONVERTOR – A device in the power train consisting of three or more rotating members. It transmits power from the engine through a fluid to the reminder of the power train and provides varying drive ratios with speed reduction and increase in torque.

TORQUE DRIVE TRANSMISSION – A transmission similar to the power glide but lacking the self shifting ability.

TORQUE TUBE DRIVE – The type of rear suspension in which the torque tube surrounding the propeller shaft absorbs the rear end torque.

TORSIONAL LOAD – Loads on the brakes and suspension caused by torque.

TORSION BAR SPRING – A long, straight bar, fastened to the frame at one end and to a suspension part at the other.

TRACKING – The following of the rear wheels, directly behind, or in the tracks of, the front wheels.

TRACTIVE FORCE – The friction force in the contact patch that causes torque on the wheel.

TRAILING SHOE – A brake shoe with its anchor at the toe end.

TRAMP – Up and down motion or hopping of the front wheels experienced at higher speeds due to unbalanced wheels or to excessive wheel run out. Also called high speed shimmy.

TRANSAXLE – A drive assembly combining the transmission and final drive assemblies in one casing.

TRANSFER CASE – A unit located at the back of the regular gear box, in the four wheel drive arrangement. A pinion fixed to the gear box shaft, drives a wheel in the transfer case. The driven wheel in the transfer case has a differential which distributes the drive equally between the front and rear axles.

TRANSMISSION – The device in the power train that provides different gear ratios between the engine and rear wheels, as well as reverse.

TRANSMISSION DRAIN PLUG – A plug at the bottom of the transmission to drain the lubricant.

TRANSMISSION FILLER PLUG – A plug on the side of the transmission used to add transmission lubricant.

TRIM HEIGHT – Specified level, vehicle height above the road surface.

TRIPLE POINT JOINT – A universal joint using bearings on three axes to maintain a constant plane of drive, making it a constant velocity joint.

TUBED TYRE – Inside the tyre, there is an endless tube fitted with a valve. Air is forced through the valve and is retained inside the tube under pressure. The air acts as the cushioning medium.

TUBELESS TYRE – A tyre that has the air sealed between the rim and tyre and does not use an inner tube.

TURNING RADIUS – The relative angles of the two front wheels during a turn.

TWO DISC CLUTCH – A clutch having two friction discs for additional holding power used in heavy duty equipment.

TYRE – The casing and tube assembled on a vehicle wheel to provide pneumatically cushioned contact and traction with the road.

TYRE BEAD – The inner reinforced edge of a tyre that holds it to the wheel rim.

TYRE CARCASS – The main structural part of the tyre to which tread rubber is attached.

TYRE CONTACT PATCH – The part of a tyre that contacts the road surface making a footprint.

TYRE FOOT PRINT – The area on the road in contact with the tyre.

TYRE FORCE VARIATION – Changes in the tyres radial spring rate as it rolls under radial loads.

TYRE SLIP – A slight tyre slide while making a turn.

TYRE ROTATION – Changing the position of tyres on the automobile to even out the amount of wear.

TYRE RUNOUT – The amount the tyre wobbles as it rotates.

TYRE SERIES – The groupings of tyre sizes having the same aspect ratio.

TYRE TREAD – is that part of the tyre that is designed to run on the road surface. The tread rubber is grooved with a pattern that will provide maximum friction force, (which provides good traction and reduces the possibility of skidding) and minimum noise.

UNDER STEER – The tendency of the vehicle not to turn as much as the wheels are turned.

UNITIZED CONSTRUCTION – A type of automobile body and frame construction in which the frame and body parts are welded together to form a single unit.

UNSPRUNG WEIGHT – That part of the vehicle which is not supported on springs (the wheels and tyres for example). The vehicle weight moved by variations in the road surface.

UNIVERSAL JOINT – The part of the drive line assembly that allows for a change in angle of the drive line as the vehicle goes over bumps.

VACUUM BRAKE – is the device in which the braking effect is due to the difference of pressures that acts on the opposite sides of a diaphragm. In this unit, one side of the piston or diaphragm is exposed to atmospheric pressure while the other side to a pressure which is below the atmospheric pressure.

VARIABLE RATE SPRINGS – provide a low rate for ordinary service and higher rate for heavy obstruction or loads. These consist of a conventional spring and below which is placed a small auxiliary spring with several leaves. Under heavy loads, the auxiliary or helper spring strengthens the main spring more and more as the main spring is compressed.

VARIABLE RATIO STEERING – A steering gear that provides a different ratio during parts of a turn.

WADDLE – A sideways vehicle shake due to a faulty radial tyre. Most noticeable when a vehicle moves slowly.

WANDER – A condition in which the vehicle does not follow a straight path and randomly drifts in one direction or the other.

WEIGHT TRANSFER – The changes in radial loads on the front and rear wheel tyres due to the centre of gravity location ring braking.

WHEELS – The wheels (wheel and tyre assembly) support the weight of the vehicle. The assembly provides ride quality, load carrying capacity, and vehicle handling characteristics.

WHEEL ALIGNMENT – The position of the front wheels in relation to the suspension and steering geometry.

WHEEL BALANCER – A device that checks a wheel, either statically or dynamically, for balance.

WHEEL BASE – Distance between center of the front wheel and center of rear wheels.

WHEEL CYLINDER – In the hydraulic braking system, hydraulic cylinders placed in the brake mechanisms at the wheels; hydraulic pressure from the master cylinder causes the wheel cylinders pistons to move the brake shoes.

WHEEL FIGHT – The tendency of a steering system to be easily deflected by uneven road surfaces. Causes changes in toe that result in tyre wear.

WHEEL OFFSET – The distance between wheel attachment flange and the wheel rim centre plane.

WHEEL PACK BEARING – A pre-assembled self-lubricated bearing assembly used on the drive wheels with independent suspension.

WHEEL SIDEWAYS DISPLACEMENT – Sideways movement of the wheel as the suspension goes from jounce to rebound.

WHEEL SIZES – are indicated by three measurements, namely rim diameter, rim width and flange height.

WHEELSLlP – Sideways movement of the tyre tread across the foot print.

WHEEL RUNOUT – The amount the wheel wobbles as it rotates.

WHEEL TRAMP – Tendency of the wheel to move up and down so it repeatedly bears hard or tramps, on the pavement. Sometimes called high speed shimmy.

WIND SHIELD WIPER – A mechanism which utilizes a rubber blade to wipe the wind shield, it is either vacuum or electrically operated.