MOTOR VEHICLE DEPARTMENT WHEELS AND TYRES MOTOR VEHICLE DEPARTMENT 05/09/06 kbuchanan

WHEELS Wheels may seem a fairly simple component on a car but in fact, a good deal of design goes into them.  Wheels are made of pressed steel, Aluminium or Magnesium alloy. Steel or Aluminium alloy are the most common. 05/09/06 kbuchanan

WHEEL DESIGN Drop centre design Drop centre section Drop centre design Wheels are usually of a drop centre design on Motor Cars. This relates to the recess created in the area where the tyre sits that is used to allow the tyre bead to drop into during removal and refitting. Semi-Drop centre Design This is a two piece designed wheel rim that has a removable outer rim to enable ease of tyre fitment. It still has recess but this is shallower than the drop centre design. (Usually used on trucks due to large tyre sizes) 05/09/06 kbuchanan

RUN FLAT RIM This design of wheel has additional recesses for the tyre bead to sit in to prevent the tyre coming off the rim when driven deflated.  A second design has a removable steel or plastic band that fits over the drop centre recess to prevent the tyre bead falling into it should the tyre become deflated. A special design of tyre must be fitted to these wheels and unlike normal tyres; they can be driven on whilst deflated 05/09/06 kbuchanan

TYRES All modern motor vehicles use a tyre filled with compressed air called a pneumatic tyre. There are two basic types of tyre construction and two methods of inflating them. Tubed tyre: This is a tyre that requires a separate ‘inner tube’ to contain the compressed air used to inflate it. Tubeless tyre: This tyre forms an airtight seal against the edge of the wheel and this contains the air used to inflate it. 05/09/06 kbuchanan

TYRE CONSTRUCTION All tyres are made up of layers of casing plies and rubber. These layers can be applied in two ways:  Cross-ply: This is where the layers are built up in an overlapping diagonally manner  Radial-ply: In this case the layers are arranged so that the casing plies are at 90 to the tyre bead. 05/09/06 kbuchanan

TYRE CONSTRUCTION Bias belted & Braced tyres   Almost all road tyres used on modern vehicles will by either bias belted or braced. These are the terms given to the radial cord layers that go around the circumference of the tyre and provide the strength to resist enlargement when inflating. (Stop the tyre going tube shaped). Textile layers are called ‘bias belted’ and steel layers are called ‘braced’ 05/09/06 kbuchanan

Marks 05/09/06 kbuchanan

REMOULD TYRES Remould Tyres - Rarely use these days a remould tyre is a tyre that has had its worn tread removed and a new piece of tread moulded onto it. They can only be used on vehicles that use a low speed rated tyre. 05/09/06 kbuchanan

TREAD PATTERNS The tread on a tyre provides the contact with the surface the car is driven on and will be tailored to various surfaces. 05/09/06 kbuchanan

RUN FLAT The Run Flat is a development that will revolutionise not only the way the car is used but also the way it is made. If the absence of the spare wheel is a major opportunity for supersport car designers and developers, the elimination of the risk of a puncture will be a real destroyer of nightmares and certainly a huge personal safety factor of advantage to all motorists. Sidewall Reinforced Run flat tyres are designed to keep the tyre beads securely anchored to the rim flange area of the wheel even when operating at zero pressure. 05/09/06 kbuchanan

RUN FLAT Support Ring 05/09/06 kbuchanan The system consists of four interdependent elements: wheel (rim), tyre, support ring and pressure loss or run-flat indicator. The principle feature of the Pax System is the way the tyre is anchored on the rim. A conventional tyre is held in place mainly by its pressure but the Pax System achieves a secure seat of the tyre bead on the rim with the help of a wedge shaped rubber element inside the casing that clamps into the rim. Any force working on the tyre only drives the wedge more firmly between rim and bead wire, thus ensuring the secure seat of the tyre on the wheel independently of the pressure inside the tyre. 05/09/06 kbuchanan

TYRE VALVE This valve is commonly also called a Schrader Valve and provides the means of inflating and deflating the tyre. Internally they are the same as a Mountain bike tyre valve, having a removable inner core with a central pin to release pressure when pressed.  Valves should be replaced when replacing a tyre and are pulled into position from the inside of the wheel well. 05/09/06 kbuchanan

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INNER TUBES 05/09/06 kbuchanan

WHEEL LOCATING AND SECURING DEVICES 05/09/06 kbuchanan

Wheel Fixings 05/09/06 kbuchanan

Wheel fixings 05/09/06 kbuchanan

ROUTINE MAINTENANCE EQUIPMENT 05/09/06 kbuchanan

REPAIRABLE AREA The repairable area T is defined as a percentage of the tyres nominal section width and is dependant on the type and size of the tyre. This chart shows the limitations that apply to the number of repairs allowed to a tyre and also the limitation on the size of the injury 05/09/06 kbuchanan

REPAIR TOOLS 05/09/06 kbuchanan

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