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Unit 4, Brakes, Wheels and Tyres, Syllabus: Brake: its need and types: Mechanical, hydraulic and pneumatic brakes, Disc and, drum type: their relative merits, Brake adjustments and defects, Power brakes, Wheels and, Tyres: their types; Tyre construction and specification; Tyre wear and causes; Wheel, balancing., BRAKE:, A brake is a mechanical device which inhibits motion., Definition of Brake System:, A brake is one of the most important controls of the vehicle. This is a combination of some, interactive parts. It absorbs energy from the moving part and slows down the vehicle with the, help of friction., Functions of Brake System:, The function of the brake system is to stop the vehicle within the smallest possible distance, and hence this is done by converting the kinetic energy of the vehicle into the heat energy, which is dissipated into the atmosphere., WORKING OF BRAKES:, •A common misconception about brakes is that brakes squeeze against a drum or disc, and, the pressure of the squeezing action slows the vehicle down. This is in fact a part of the, reason for slowing down a vehicle., •Actually brakes use friction of brake shoes and drums to convert kinetic energy developed, by the vehicle into heat energy., •When we apply brakes, the pads or shoes that press against the brake drums or rotor convert, kinetic energy into thermal energy via friction., Thus brakes are essentially a mechanism to change energy types, , Types of Braking system in Automobile;, By applications –, 1. Foot Brake,, 2. Hand brake., By Method of power –, 1. Mechanical brake,, 2. Hydraulic brake., 3. Vacuum brake,, 4. Electrical brake and, 5. Air brake., By method of operations –, 1. Manual brake,, 2. Servo brake., 3. Power operation., By construction –, 1. Drum type brake,, 2. Disc type brake.

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Terminology, , , , , , , , , , , Steel Wheels – A very popular, design of wheel. Very strong, and cheap to produce., Alloy Wheels – Attractive and, light weight, but can be difficult, to clean., Spoked Wheels – Used on, older sports vehicles, but, cannot be fitted with tubeless, tyres., Divided rims – the rims are, made in two halves which are, bolted together, the rims must, never be separated while the, tyre is inflated., Split rims – the tyre is held in, place by a large circlip, do not, remove the tyre unless you, have been properly trained, , , , , , , , , , , , , , Radial Ply Tyre – the main, plies of the tyre run at 90, degrees from one bead to the, other., Cross Ply Tyre – the main, plies of the tyre run at 45, degrees from one bead to the, other., Plies – Layers of strong fabric, which are built up to give the, tyre its strength and shape, Bead – loops of steel which, are the anchorage point for the, plies., Tread – this provides the grip, with the road surface, the, pattern assists in clearing any, water away, Side Wall – this connects the, beads to the tread of the tyre.

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Wheel - Basics, Most standard wheels are made of steel., Some vehicles are fitted with alloy, wheels that are made of, magnesium or aluminium., The rim holds the tyre., The well of the wheel allows the, tyre to be removed and refitted, , Rim, , The centre section is, welded to the rim., The pilot bore fits to the hub., Centre mounting section, Next >

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Valve Stems and Cores –, Three functions – It retains the air, it, allows inflation and deflation., , Valve core, , The rubber stem of the valve is, pulled into the wheel., , Valve stem, , Seat, washer, , The valve core contains a, spring loaded air valve insert., , The valve core also has a sealing, washer and a seat washer., The valve cap keeps out, dust and helps keep air in., , Sealing, washer, , Tyre pressures must only be checked and, adjusted when the tyre is cold, , Valve caps, , Next >

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Wheel Fixings, Wheel studs and nuts attach the, wheel to the hub., , Taper, , The wheel studs press through, the hub or axle flange., The taper on the wheel nuts, secures and centres the wheel., Wheel studs usually have a, right-hand thread., If it is a left-hand thread, it can be, marked with “L”., Metric threads can be marked with “M”, or METRIC., , Wheel mounting, Hub flange, Next >

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Wheel Nut Torque, Correct torque of wheel fixing is, vital for all vehicles, and nearly, all require the use of a, torque wrench., Excessive torque can lead to, wheel or hub distortion, causing, runout and vibration., Low torque may allow wheel, nuts to work loose and wheels, to come off., Nuts should be tightened in a, diagonal pattern., , Torque, wrench

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Wheel Sizes

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Tyres (Introduction), , , , , , , , , Basis Functions, The tyre acts as the primary suspension,, cushioning the vehicle from the effects of a, rough surface., It also provides frictional contact with the road, surface., This allows the driving wheels to move the, vehicle., The front tyres allows the wheels to steer ., The tyres allow the brakes to slow or stop the, vehicle

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Pneumatic Tyres, , , , , , , , The tyre is a flexible casing, which contains air., Tyres are manufactured from reinforced synthetic, rubber., The tyre is made from an inner layer of fabric plies,, which are wrapped around bead wires at the inner, edges., The bead wires hold the tyre in position on the wheel, rim., The fabric plies are coated with rubber, which is moulded, to form the side walls and tread of the tyre. Behind the, tread is a reinforcing band, usually made of, steel,rayon,or glass fibre. Modern tyres are mostly, tubeless, so they have a thin layer of rubber coating, inside to act as a seal.

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Tyre Construction, • Cross – ply tyres are not used, on any mass produced modern, cars. However, the, construction details are useful, to show how tyre technology, has developed., • Several textile plies are laid, across each other, running, from bead to bead in alternate, directions., • The number of plies depends, on the size of the tyre and the, load it has to carry., • The same number of plies is, used on the crown and the, sidewalls.

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Tyre Construction, • Radial – Ply tyres consist of a, carcass ply formed by textile, arcs running from one bead to, the other., • Each ply which is laid in an arc, at an angle of 90 degrees to, the direction the tyre rolls., • At the top of the tyre crown, (under the tread), there is a, belt made up of several plies, reinforced with metal wire, laid, on top of the carcass ply., • These crown plies, laid one on, top of the other, overlap at an, angle determined by the type, of the tyre.

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Tyre Specifications, , P 205/55 V R 16, TYPE, P - PASSENGER, T - TEMPORARY, LT - LIGHT TRUCK, C - COMMERCIAL, , RIM DIAMETER, (INCHES) 13, 14 ETC, , ASPECT RATIO, (HEIGHT/WIDTH %), 55, 60, 65 70 ETC, , WIDTH, (MILLIMETERS), 145-315, , TYPE, B - BIAS-BELTED, D - DIAGONAL BIAS, R - RADIAL, , SPEED RATING, B (31 MPH) V (150 MPH) Z (OVER 150 MPH), Next >

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Special Service Tyre, This is a space-saver spare tyre., Used to replace flat tyre., It is not used for rotation, (swapping)., It uses a special wheel., Speed and pressure, restrictions apply., It has no hub caps or wheel covers., Next >

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• Remember the tyre tread depth must be not less than 1.6mm over the, central three-quarters of the tyre and must go all the way round the, circumference in an continuous unbroken band with no bald patches, anywhere on the tyre tread., • If radial and crossply tyres are fitted to the same vehicle, the radial-ply, tyres must only be fitted to the rear., • Cross-ply and radial ply tyres must never be fitted to the same axle., • Tyre pressures must be set to the manufactures recommendations, • The tread and side wall must be free from large cuts, abrasions or, bubbles

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Balance, Wheel imbalance causes wheel, tramp, or hop, makes the tyre, vibrate up and down., Centrifugal forces try to throw, heavy areas outward when the, wheel is spinning., , Weight must be evenly distributed, around the axis of rotation., Imbalance can be rectified in one of two, ways by Static Balancing (stationary), or Dynamic Balancing (spinning).

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Rotation, A system of rotation is used to even out tyre, wear and reduce the need for re-balancing., , (a), , (b), , (c), , (d), , (a) 4-wheel bias (cross-ply) tyre rotation., (b) 5-wheel rotation (including spare)., Radial tyres must be kept on the same, side of the car., (c) 4-wheel radial tyre rotation., (d) 5-wheel radials (including spare)., Care must be taken with spare as some, modern tyres are directional.

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Causes, behind the, Uneven, Tire Wear

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Finding out a new, tire for the car often, comes as a surprise.

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Tires of the car need a, frequent replacement, for below reasons:, Driving too speed, , Drive like a crazy, Mash the accelerator, Slam on the brakes

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Uneven tire wear, indicates the, constant wearing, away tires.

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Premature or uneven, tires wear caused for, several factors:, Faulty tire pressure, Loose suspension components, Misaligned wheels, Leaking steering parts

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Uneven tire wear can, be caused for belowdefined reasons.

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Damaged steering, components

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When the steering, components of the, car are damaged, it, will indicate:, Loose ball joint, , Worn out tie rod end, Excessive moving rack and, pinion

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As a result, it will, scrub the tires and, excess friction cause, tire tread wear.

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Wrong tire pressure

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Over-inflated tires can, wear out the center of, the tire tread faster.

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Under-inflated tires, can wear out the, inner and outer tire, shoulder quickly.

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Loose suspension parts

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Worn out suspension, parts of the car indicate, several signs:, Leaking strut, , Broken coil spring, Worn out shock

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When the suspension, parts are damaged, it, will cause uneven tire, wear.

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Improper wheel alignment

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Wheel alignment of, the car plays a vital, role in tire wear.

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Incorrect angled, tires will cause, excessive tire wear, and affect the, wheels.

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Prevent tire wear

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Through routine, maintenance one can, prevent tire wear. Such, as:, Tire pressure adjustments, Regular car tire inspection, , Four-wheel alignments

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Affected tires need, rotation on a regular, interval for less, susceptible wear.

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Replace the tires of the, car by a reputed and, qualified mechanic.