Automobile Wheels Types of Wheels

Automobile wheels:

A wheel is a circular block of a hard and durable material at whose center has been bored a circular hole through which is placed an axle bearing about which the wheel rotates when a moment is applied by gravity or torque to the wheel about its axis, thereby making together one of the six simple machines i.e. wheels and axles.

Automobile wheel is the metal part of the wheel-assembly without tyre, tube, hub, bearings and the axle.

The common types of wheels are:

1. Wire/spoke wheel
2. Disc wheel: passenger and heavy-vehicle wheels
3. Alloy wheel

The functions of wheel in the automotive vehicle are;

1. To observe the impact forces of the road surface and to bear the vehicle load.
2. Transfers the rotational movement of the axles to Tyres and are steered.
3. Absorbs and transfers the braking and Accelerating forces as well as cornering forces.
4. Dissipates the braking heat to the atmosphere and
5. Acts as a seal in case of tubeless tyres.

Presently the trend is towards the use of light-alloy wheels made of aluminum and magnesium alloys. These are light weight, almost corrosion free, and casted in single piece. Automobiles light trucks/SUVs are equipped with a single piece wheel i.e. alloy wheel. Larger vehicles have a lock ring (side ring) that allows for the easy removal of the tyre from the wheel and, when in place, it provides a seat for one side of the inflated tyre.

Wheels can be made from cast aluminium alloy or magnesium alloy. Alloy wheels are popular because of their appearance and because they are lighter than similar steel wheels. Aluminium is a better conductor of heat, so alloy wheels can dissipate heat from brakes and tyres more effectively than steel ones. Most wheels have ventilation holes in the flange, so air can circulate to the brakes.

Details description of different types of wheels used on various automobiles are as follows:-

1. Wire wheel:

The wire wheel has a separate hub which is attached to the rim through the number of wire spokes. The headed inner ends of the spokes fit in the hub holes and the threaded outer ends fit in the rim holes. The spokes carry the weight, transmit the driving and braking torques and withstand the side forces while cornering, in tension. Spokes are long, thin wires and as such these cannot take any compressive or bending stresses. All types of loads are sustained by the spokes in tension .The spokes are mounted in a complicated criss-cross fashion installed in the three planes. 

This arrangement or spokes serve special purpose of the wheel. The component of vehicle weight in the direction of spokes above the hub is sustained by these spokes in tension. Similarly, the driving and the braking torques are taken up by the tension in the spokes in the desired direction as shown by fig respectively.

The side forces on cornering are taken up by the spokes forming triangular arrangement. Thus it is seen that the spokes have to be mounted on the wheel. The initial tension of the spokes can be adjusted by means of screw nipples which also serve to secure the spokes to the rim. The hub is provided with internal splines to correspond to the splines provided on the axle shaft. A wing nut screws the hub on the axle shaft. 

The advantages of this type of wheel are light weight and high strength, and above all it provides much better cooling of the brake drum. It is also easy to change the wheel when required, because only one nut has to be opened. However, wire wheels are expensive due to their intricate construction. The rim of a wired wheel is not capable to fit tubeless tyres.

2. Disc wheel:

This type of wheel consists of a steel rim and a pressed steel disc. The rim is rolled section, sometimes riveted but usually welded to the flange of the disc. The disc performs the function of spokes. A hole in the rim serves to accommodate tube valve. The wheel hub is fitted on the axle. Some slots are generally provided in the wheel disc to allow the air to pass to the inner side for better cooling of the brake drum inside. 

Since these holes tend to weaken the disc, the holes in modern wheels are swaged which means that some portion of the disc around each hole is turned inward smoothly to compensate for the loss of strength due to holes. A separate cover is also provided on the wheel disc called wheel cap. This type of wheel is simple, cheap and robust in construction. It is most commonly used in passenger as well as in heavy motor vehicles ex. buses, cars, trucks, tractors, etc.

The rim and the disc may be, permanently attached or attachable, depending upon design. A typical steel disc wheel is shown in fig, in which the pressed steel disc is welded to the rim.

Heavy - vehicle wheels are made in the same way as the disc wheels but much thicker plate is used. To lighten the wheel and also to increase air flow to the brake drum, large holes are made around the disc. The wheel nut recesses are usually machined instead of being embossed.

3. Alloy wheel (Mag wheel):

The latest trend in case of automobile wheels is the use of wheels made from aluminum or magnesium alloys cast wheels are generally used for cars while forged wheels are preferred for wheels of heavier vehicles. The main advantage of light-alloy wheels is their reduced weight which reduces unsprung weight. 

A magnesium alloy wheel weighs about 50 per cent of a steel wheel and about 70 per cent of an aluminum alloy wheel for similar strength. Moreover, light alloys have better conductivity of heat which helps the wheels to dissipate heat generated by the tyres or brakes and thereby run cooler. Further, wider rims improve stability on cornering. Through cast or forged wheels have to be machined, yet this helps to maintain close tolerances and also produce better appearance. 

Magnesium alloys have high impact and fatigue strength so that they can stand vibrations and shock loading better. However, being tune to corrosion, these have to be given some protective coating. Aluminum alloys do not have high resistance to vibration and shock as in case of magnesium alloys, but these are relatively easier to cast or forge and also less tune to corrosion. 

Generally, aluminum alloys are used for cars sports and racing cars usually have magnesium alloy wheels. Higher cost is the only disadvantage of light alloy wheels.

Note: Figure name indication- please move your cursor on image.

Next article: "Wheel Rims"