Wheels And Rims
Introduction
● The wheel and tyre assembly is the last member in the drive line of transmission system. Wheels are connected to rear axle,
● As the rear axle rotates, the wheel also rotate and vehicle moves on the road. The wheel assembly is consisting of hub disc or spoke, rim, tyre and tube.
● The main function of wheel is to support the load of the vehicle and passengers and to resist the side force,turning called lateral load.
● The wheel also transmit engine driving torque and braking torque to the tyre while driving and braking called as tractive load.
(a) Function of wheel
The wheel must perform the following functions:
1. It should support the load of the vehicle, brake system mounting and the passengers.
2. It should resist the side for caring turning called lateral load.
3. The wheel also transmit engine driving torque and braking torque to the tyre while driving and braking called as tractive load.
4. It was the steering system of the vehicle.
5. It should also the shock caused by road irregularities
(b) Necessity and Requirements of Wheel
To perform the above functions the wheel must be
1. It should be strOng eNough to withstand the weight of the vehicle.
2. It should be perfectly balanced statically and dynamically.
3. It should be light in weight and easily remarkable.
4. It should be able to grip the road surface.
5. It should not deteriorates with weather condition and age (cracking, corrosion).
Types of Automobile Wheels:
Three main types of wheels are in use today:
(1) Pressed steel disc wheel
(2) Wire or spoke wheels
(3) Light alloy casting wheels
(a) Construction and working of pressed steel disc wheel
● Now a days these wheels are widely used for cars.
● These are light, strong, cheap and resistant to accidental damage.
● This type of wheel consists of two parts, namely rim and the disc member welded together.
● When the bead of the tyre is resting in the well, it is possible to pass the tyre over the opposite edge of the rim.
● The seat of the rim where the tyre rests has 5 to 15" taper so as the tyre is inflated, the beads are forced up the taper to give a wedge fit with tubeless tyre, the taper helps to make a good seal.
● The wheels are secured to the axle by four or five bolt spaced equally in a circle around the hub flanges.
● Some slots are provided in the wheel disc to allow the air to pass to the inner side for better cooling the brake drum inside. A hole in the rim serves to accommodate tube valve.
● A wheel constructed in two parts which when fastened together combines to form called a divided wheel.
(b) Wire or spoke wheels
● These wheels are lighter, stronger and springy.
● It consists of a separate hub which is attached to rim through number of wires called spokes. These spokes are mounted in a complicated criss-cross fashion in all the three plane.
● The component of vehicle weight in the direction of spokes above hub is sustained by these spokes in tension. The braking and driving torque are taken by spokes.
● The side forces during comering are taken by the spokes forming triangular arrangement
● The initial tension in the spokes can be adjusted by screw nipples which also serve to secure the spokes to the rim.
● The hub is provided with internal spline to corresponding spline on axle shaft.
Advantages
1. These are light weight and have high strength.
2. It provides better cooling of the brake drum due to better air flow around the brake drum and heat dissipation capacity.
3. It is very easy for changing the wheel as only one nut has to be opened.
Disadvantages
1. These are difficult to clean.
2. Spokes tend to work loose in service.
3. As rim has a hole for nipples, it is not possible to fit tubeless tyre.
4. These are expensive due to complicate in construction
(c) Cast Light Alloy Wheel
● Cast alloy wheels are made from casting of light alloy of aluminium or magnesium.
● They have wider rims and radial ribs which also acts as an angled spokes to provide strength and air circulation and also reduce noise and vibration.
● Wider rims are provides stability during cornering.
● Stove enameling of alloy improve appearance and provide corrosion resistant property
● Cast wheels are generally used for car while forged wheels are preferred for heavy vehicles.
● Heavier section of wheel can be used which improve the stiffness and result in better stress distribution.
Advantages
1. These are lighter in weight which reduces unsprung weight of vehicle.
2. These are better conductor of heat which helps in heat dissipation during braking action, provide better brake drum coling.
3. It improves stability on cornering.
4. These have high impact and fatigue strength their by better shock absorption capacity
Disadvantages
1. Higher manufacturing cost because of precision machining to maintain close tolerance.
2 Poor resistance to corrosion hetice protective coating should be provided over it.
Necessity and function of Rims:
● Rim provide leverage and reduce friction when the vehicle is moving.
● The rim works is to rotate round the tyre roads.
● These are essential for all automobile for commercial and passenger vehicle.
● The size of rim is dependent of the weight impacted by vehicle and pavement in order to provide leverage. Rim determine performance of ride comfort.
● Size of rim affect braking. handling, acceleration, alignment and speedometer calibration.
Requirements of Rims:
● It should have static strength
● It must have fatigue strength.
● It must possess impact strength.
It must deform under all type of load.
Types of Rims, their Construction and Working :
● Rim is well type of structure in which the tyre is contained.
● The rims are generally of two types:
(1) Drop centre rim.
(2) Flat base rim
● Drop centre rims are generally used in two wheeler whereas flat base rims are used in commercial vehicle. The rims are made of steel or aluminum
● Also rim again classified into flat base three piece rim, semi drop centre and flat base divided type. For car tyre, well base or drop centre is the common tyre.
● The tyre is pressed into the races of the drop centre well for leveling in opposite side over the rim flange. A slight type is of 5° provided for riding up the bead due to air pressure in the tyre.
● Flat base three piece rim is a detachable flange rim. It is used with stiff and heavy beads tyre fitted on heavy vehicles.
● The flange is held in position by a split lock ring similar to larger circlip. The lock ring may be removed after pushing the flange toward the tyres.
● Semi drop centre rim is a two piece rim. It is compromises between well base and flat base rim It is suitable for light vehicle.
● Its removal is simplified by a split, detachable flange while the tyre is locked to the rim by a slight taper, when the tyre is removed the slight well may be used.
● Flat base divided type rim used mainly in military vehicle, It is makin two halves which am lord together by ring of nut adjacent to the rim.
● For changing wheel these nuts should never be removed.
● The wheel rim diameter is influenced by
1.The size and weight of the vehicle.
2. The ground clearance and
3. Space required for the brakes and suspension components etc.
