Wheels and Tyres Topics covered in this presentation: Tyres Wheels

Terminology 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. 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

Centre mounting section 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. Centre mounting section The pilot bore fits to the hub. Next >

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 Sealing washer 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. Tyre pressures must only be checked and adjusted when the tyre is cold Valve caps Next >

Wheel Fixings Wheel studs and nuts attach the wheel to the hub. Taper Hub flange Wheel mounting 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. Next >

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

Wheel Sizes

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

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.

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.

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.

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

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 >

Remember the tyre tread depth must be not less than 1 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

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).

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