CHASSIS
1 INTRODUCTION
“Chassis” a French term which means the complete Automobiles without
Body and it includes all the systems like power plant, transmission, steering, suspension, wheels tyres, auto electric system etc. A vehicle without body is called as a chassis. If Body is also attached to it them it is known as the particular vehicle as per the shape and design of the body.
1.1 BASIC LAYOUT OF CHASSIS FRAME

Figure 1 Chassis layout
Figure 1 shows the layout of chassis. It shows that the engine is located at the front end of the vehicle. It is connected to the gear box through clutch.
The drive of the engine can be connected or disconnected from the gearbox with the help of the clutch pedal. From the gearbox, the power is transmitted to the differential through propeller shaft and finally to the wheels via rear axles.

2 MAIN COMPONENTS OF CHASSIS
2.1 FRAME
The frame is the main part of the chassis on which remaining parts of chassis are mounted. The frame should be extremely rigid and strong so that it can withstand shocks, twists, stresses and vibrations to which it is subjected while vehicle is moving on road. It is also called under body.
The frame is supported on the wheels and tyre assemblies. The frame is narrow in the front for providing short turning radius to front wheels. It widens out at the rear side to provide larger space in the body.
2.1.1 FUNCTIONS OF FRAME
1. To carryall the stationary loads attached to it and loads of passenger and cargo carried in it .
2. To withstand torsional vibration caused by the movement of the vehicle
3. To withstand the centrifugal force caused by cornering of the vehicle
4. To control the vibration caused by the running of the vehicle
5. To withstand bending stresses due to rise and fall of the front and rear axis.
2.1.2 TYPES OF FRAME
There are three types of frames:
(a) Conventional frame.
(b) Semi-integral frame.
(c) Integral frame (or unit frame).

a) Conventional Frame
It is non-load carrying frame. The loads of the vehicle are transferred to the suspensions by the frame. This suspension in the main skeleton of the vehicle which is supported on the axles through springs.
The body is made of flexible material like wood and isolated frame by inserting rubber mountings in between. The frame is made of channel section or tubular section of box section.

Figure 2 Conventional frame it has advantages of strong chassis of small proportional weight sufficient to carry the considerable pay loads, localized accident damage which is easy to repair in comparison to the integral chassis.

b) Semi-integral Frame
In this case the rubber mountings used in conventional frame between frame and suspension are replaced by more stiff mountings. Because of this some of the vehicle load is shared by the frame also. This type of frame is heavier in construction.
In semi integral type half frame is fixed in the front end on which engine gear box and front suspension is mounted. It has the advantage when the vehicle is met with accident the front frame can be taken easily to replace the damaged chassis frame.

Figure 3 Semi integral frame

c) Integral Frame or Frame-less Construction
In this type of construction, there is no frame. It is also called unitized frame-body construction. In this case, the body shell and under body are welded into single unit.
The under body is made of floor plates and channel and box sections welded into single unit. This assembly replaces the frame. This decreases the overall weight compared to conventional separate frame and body construction.

Figure 4 Integral frame

2.2 SUSPENSIONS
The frame and body of an automobile are mounted on front and rear axles through springs and shock absorbers. If it is mounted directly on axles, all the socks and vibrations will be transmitted to body causing discomfort to the passengers. The springs and shock absorbers are used to damp the shocks and vibrations. The suspensions system includes all those parts which are used to perform the damping action. Besides, springs and shock absorbers, a suspension system includes other mountings also. The suspension system of a vehicle is divided into front suspension and rear suspension.

2.2.1 FUNCTIONS OF SUSPENSION SYSTEM
(a) The main function of a suspension system is to prevent the socks to transmit to car or vehicle body so that passengers may ride comfortably.
(b) To maintain the stability of vehicle during pitching and rolling actions while the vehicle is in motion.
(c) To provide better road holding at the time of driving, braking and cornering.
(d) To allow proper steering geometry.

2.2.2 TYPES OF SPRINGS IN SUSPENSION SYSTEM
a) Coil spring
b) Leaf spring
c) Torsional bars

a) Coil springs
Coil springs are in the form of helix. These are made from special steel.
It is made from steel wire in the form of a coil. The coil springs absorb energy when this spring is compressed while vehicle moves over road bump. The coil springs are mainly used in independent suspension.
However, these can also be used in the conventional rigid axle suspension. Coil springs are capable of resisting shear and bending stresses but not torsion and side thrust. When coil springs are used in the suspension system, other arrangements are made to bear torsion and side thrust.

Figure 5 coil spring

b) Leaf spring
These springs are made by placing several flat strips one over the other.
These are made of steel plates. One flat strip is called a leaf. Lowest leaf is of smallest length and the length of other leaves placed above this keeps on increasing progressively. In this way, the length of top most leaf (main leaf) largest. Main leaf has eyes at the ends. All the leaves are clamped together at centre and sides by the centre bolt and side clamps respectively. The centre portion of the leaf springs is connected to the axle with the help of U-bolt.
Automobile Engineering Spring eye is used to attach spring to the body frame by passing a bolt through one eye. Other end of leaf spring is attached to a shackle through its eye. Shackle is in turn attached to chassis. The shackle is used to accommodate any change in length of spring due to its expansion and contraction. The contraction and expansion takes place when the vehicle passes over road surface irregularities. Semi-elliptical springs are generally used in all the vehicles particularly n trucks. In case, leaf springs were used in rear suspension and independent suspension in the front.

Figure 6 Leaf spring

c) Torsional bars
Torsion bar is a steel rod which an take torsional and shear stresses.
Torsion bar acts as spring and keeps the lower and upper control arm parallel.
The torsion bar is shown in Fig. One end of the rod is made of hexagonal xsection which fits into lower control arm. Other end is also hexagonal x-section which fits into an anchor attached to an anchor. When any force acts on the wheel assembly, the torsion bar gets twisted. The wheel axle is supported by lower control arm. The torsion bar is connected to lower control arm. The torsion bar is used to keep the lower arm at a given height. This suspension
(torsional bar) provides cushion to road shocks by allowing the lower arm to twist the torsion bar. The torsion bar occupies normal condition when the wheels are not under any stress. When the wheels move up and down the torsion bar is twisted and it absorbs the vibrations so generated.

Figure 7 Torsion bar

2.3 SHOCK ABSORBERS
If only springs are used to absorb shocks, the oscillations of springs continue even after the vehicle has passed over a bump. The oscillations cause the wheels the jumps up and fall down till the oscillations die out. Thus, dampers or shock absorbers are used to arrest the oscillation of springs after the vehicle passes over irregular road surface. Shock absorbers are necessary used with coil springs. In case of leaf springs, the friction between leaves provides some dampening effect. However, this is not sufficient sometimes, depending upon friction between leaves. Hence, shock absorbers are necessarily used as additional damping devices.
2.3.1 Function of Shock Absorbers
As explained earlier, the function of the shock absorber is to dampen the vibrations of coil and leaf springs used in the suspension system. These vibrations are generated when vehicle passes over a road bump.

Figure 8 Shock absorbers

2.4 TYRES Tyres

are mounted on the rims of wheels. They enclose a tube between

rim and itself. Air is filled at a designated pressure inside the tube. The tyre remains inflated due to air pressure inside tube. The tyre carries the vehicle load and provides cushioning effect. It absorbs some of the vibrations generated due to vehicle’s movement on uneven surfaces. It also resists the vehicle’s tendency to over steer or turn which cornering. Tyre must generate minimum noise when vehicle takes turn on the road. It should provide good grip with the road surface under all conditions.
2.4.1 TYPES OF TYRES
Two types of tyres are used in vehicles :
(a) Tube tyres
(b) Tubeless tyres.
Both these tyres are called pneumatic tyres because air is filled in them.
a) Tube Tyres
Tube tyres encloses a tube which is wrapped on the wheel rim. Air is forced into tube which inflates the tube and tyre. The outer side of tyre which comes in contact of road is made from rubber. It is called tread. Tread provides resistance to slipping. It is very thick at the outer periphery. Beads are made at the inner bide by reinforcing it with steel wires. Beads are very strong which have good resistance to wearing against the wheel rim. Rayon cords are also formed into a number of piles. Beads are cords provide good strength to tyres.

b) Tubeless Tyres
These tyres do not require any tube. The air at pressure is filled into the tyre itself. The construction of tyre is same as that of tube tyre. For filling the air, a non-return valve is filled in the tyre itself.
Advantages of Tubeless Tyres
(a) Tubeless tyres are lighter in weight.
(b) They remain cooler compared to tube tyres.
(c) The main advantage of tubeless tyre is that they remain inflated for long time even if these are punctured by a nail if the nail remains inside the tyre.
(d) Any hole in the tyre, due to puncture, can be repaired by rubber plugging.
(e) A simple puncture can be repaired without removing tyre from wheel.
2.4.2 TYRE SPECIFICATION
Every tyre is specified by its size. Its specification is given as follows :
8.25 × 30 × 6 PR
Meaning of these Numbers
(a) 8.25 : It mean that thickness of tyre from shoulder to shoulder is 8.25 inches.
(b) 20 : It means that diameter of bead circle is 20 inches.
(c) 6 PR : It means that six ply rating. It means that tyre consists of 6 plies.
Different type of tyres has different plies. Number of plies increase as load increases, e.g. a car tyre has 4 to 6 plies and a light truck may have 6 to 10 plies.

2.5 ENGINE, CLUTCH AND GEAR BOX
2.5.1 IC ENGINE
An engine is a machine designed to convert one form of energy into mechanical energy. Heat engines, including internal combustion engines and external combustion engines (such as steam engines), burn a fuel to create heat, which then creates a force.
The internal

combustion

engine is

an

engine

in

which

the combustion of a fuel (generally, fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine the expansion of the high temperature and high pressure gases, which are produced by the combustion, directly applies force to components of the engine, such as the pistons or turbine blades or a nozzle, and by moving it over a distance, generates useful mechanical energy.

Figure 9 Engine

2.5.2 CLUTCH
A clutch is

a

mechanical

device

that

engages

and

disengages

the

power transmission, especially from driving shaft to driven shaft.
Clutches are used whenever the transmission of power or motion must be controlled either in amount or over time (e.g., electric screwdrivers limit how much torque is transmitted through use of a clutch; clutches control whether automobiles transmit engine power to the wheels).
In the simplest application, clutches connect and disconnect two rotating shafts
(drive shafts or line shafts). In these devices, one shaft is typically attached to an engine or other power unit (the driving member) while the other shaft (the driven member) provides output power for work. While typically the motions involved are rotary, linear clutches are also possible.
In a torque-controlled drill, for instance, one shaft is driven by a motor and the other drives a drill chuck. The clutch connects the two shafts so they may be locked together and spin at the same speed (engaged), locked together but spinning at different speeds (slipping), or unlocked and spinning at different speeds (disengaged).

Figure 10 Clutch

2.5.3 GEAR BOX
A gearbox is a mechanical method of transferring energy from one device to another and is used to increase torque while reducing speed. Torque is the power generated through the bending or twisting of a solid material. This term is often used interchangeably with transmission.
Located at the junction point of a power shaft, the gearbox is often used to create a right angle change in direction, as is seen in a rotary mower or a helicopter. Each unit is made with a specific purpose in mind, and the gear ratio used is designed to provide the level of force required. This ratio is fixed and cannot be changed once the box is constructed. The only possible modification after the fact is an adjustment that allows the shaft speed to increase, along with a corresponding reduction in torque.
In a situation where multiple speeds are needed, a transmission with multiple gears can be used to increase torque while slowing down the output speed. This design is commonly found in automobile transmissions. The same principle can be used to create an overdrive gear that increases output speed while decreasing torque.
In an automobile, there are three types of transmission: automatic, manual, or continuously variable. A manual transmission vehicle provides the best example of a simple gearbox. In both the automatic and continuously variable transmissions, the gearboxes are closed systems, requiring very little human interaction.
Manual transmission is available in two different systems: sliding mesh and constant mesh. The sliding mesh system uses straight cut spur gears.
The gears spin freely and require driver manipulation to synchronize the

transition from one speed to another. The driver is responsible for coordinating the engine revolutions to the road speed required. If the transition between gears is not timed correctly, they clash, creating a loud grinding noise as the gear teeth collide. The constant mesh system has diagonally-cut helical or double helical gear sets that are permanently meshed together. Friction cones or synchronized rings have been added to the gears to create a smoother transition when changing gears. This type of transmission is usually found in racing cars and agricultural equipment.

Figure 11 Gear box

2.6 RADIATOR
Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. To cool down the engine, a coolant is passed through the engine block, where it absorbs heat from the engine. The hot coolant is then fed into the inlet tank of the radiator (located either on the top of the radiator, or along one side), from which it is distributed across the radiator core through tubes to another tank on the opposite end of the radiator. As the coolant passes through the radiator tubes on its way to the opposite tank, it transfers much of its heat to the tubes which, in turn, transfer the heat to the fins that are lodged between each row of tubes. The fins then release the heat to the ambient air. Fins are used to greatly increase the contact surface of the tubes to the air, thus increasing the exchange efficiency. The cooled coolant is fed back to the engine, and the cycle repeats. Normally, the radiator does not reduce the temperature of the coolant back to ambient air temperature, but it is still sufficiently cooled to keep the engine from overheating. Figure 12 Radiator

2.7 PROPELLE SHAFT
Propeller shaft, sometimes called a carden shaft, transmits power from the gearbox to the rear axle. Normally the shaft has a tubular section and is made in one- or two-piece construction. The two-piece arrangement is supported at the midpoint by a rubber mounted bearing. Short drive shafts are incorporated for the transmission of power from the final drive assembly to the road wheels in both front and rear wheel drive layouts.
This shaft must be strong to resist the twisting action of the driving torque and it should be resilient to absorb the torsional shocks. It must resist the natural tendency to sag under its own weight because vibration occurs when the centre of gravity does not coincide with the axis of the shaft.
Since propeller shafts of road vehicles are sufficiently long and operate in general at high speed, whirling may occur at certain critical speed. This produces bending stresses in the material that are higher than the shearing stresses caused by transmitted torque. While the critical speed increases with decrease in the mass of the shaft, the moment of inertia of the section increases.
The tendency for the propeller shaft to whirl should be reduced and to do so, it should be made tubular and should be perfectly balanced.

Figure 12 Propeller shaft

2.8 DIFFERENTIAL UNIT
2.8.1 TO PROVIDE TURNING
In automobiles the differential allows the outer drive wheel to rotate faster than the inner drive wheel during a turn. This is necessary when the vehicle turns, making the wheel that is traveling around the outside of the turning curve roll farther and faster than the other. The average of the rotational speed of the two driving wheels equals the input rotational speed of the drive shaft. An increase in the speed of one wheel is balanced by a decrease in the speed of the other.

When used in this way, a differential couples the input shaft (or prop shaft) to the pinion, which in turn runs on the crown wheel of the differential.
This also works as reduction gearing to give the ratio. On rear wheel drive vehicles the differential may connect to half-shafts inside an axle casing or drive shafts that connect to the rear driving wheels. Front wheel drive vehicles tend to have the pinion on the end of the main-shaft of the gearbox and the differential is enclosed in the same casing as the gearbox. They have individual drive-shafts to each wheel.

A differential consists of one input, the drive shaft, and two outputs which are the two drive wheels, however the rotation of the drive wheels are coupled by their connection to the roadway. Under normal conditions, with small tyre slip, the ratio of the speeds of the two driving wheels is defined by the ratio of the radii of the paths around which the two wheels are rolling, which in turn is determined by the track-width of the vehicle (the distance between the driving wheels) and the radius of the turn.

2.8.2 TO REDUCE LOSS OF TRACTION
One undesirable side effect of a conventional differential is that it can limit traction under less than ideal conditions. The amount of traction required to propel the vehicle at any given moment depends on the load at that instant how heavy the vehicle is, how much drag and friction there is, the gradient of the road, the vehicle's momentum, and so on.

The

torque

applied

to

each

driving wheel is

a

result

of

the engine, transmission and drive axles applying a twisting force against the resistance of the traction at that road wheel. In lower gears and thus at lower speeds, and unless the load is exceptionally high, the drivetrain can supply as much torque as necessary, so the limiting factor becomes the traction under each wheel. It is therefore convenient to define traction as the amount of torque that can be generated between the tire and the road surface, before the wheel starts to slip. If the torque applied to one of the drive wheels exceeds the threshold of traction, then that wheel will spin, and thus only provide torque at each other driven wheel limited by the sliding friction at the slipping wheel. The reduced net traction may still be enough to propel the vehicle.

A conventional "open" (non-locked or otherwise traction-aided) differential always supplies close to equal (because of limited internal friction) torque to each side. To illustrate how this can limit torque applied to the driving wheels, imagine a simple rear-wheel drive vehicle, with one rear road wheel on asphalt with good grip, and the other on a patch of slippery ice. It takes very little torque to spin the side on slippery ice, and because a differential splits torque equally to each side, the torque that is applied to the side that is on asphalt is limited to this amount.

What Happens In a Regular Differential?
1. The drive shaft turns a crown wheel.
2. The crown wheel rotates, rotating the planet pinions. However, the planet pinions are not spining they are revolving.
3. The planet pinions turn the sun gears.
4. The sun gears spin and turn the axels, which turns the tires.

Figure 13 Differentional unit

2.9 UNIVERSAL JOINT
A universal joint is a mechanical device that allows one or more rotating shafts to be linked together, allowing the transmission of torque and/or rotary motion. It also allows for transmission of power between two points that are not in line with each other.
Universal joints are capable of transmitting torque and rotational motion from one shaft to another when their axes are inclined to each other by some angle, which may constantly vary under working conditions.
Universal joints are incorporated in the of vehicle’s transmission system to perform three basic applications:
(a) Propeller shaft end joints between longitudinally front mounted gearbox and rear final drive axle.
(b) Rear axle drive shaft end joints between the sprung final drive and the un sprung rear wheel stub axle.
(c) Front axle drive shaft end joints between the sprung front mounted final drive and the un sprung front wheel steered stub axle.
Universal joints have movement only in the vertical plane when they are used for longitudinally mounted propeller shafts and transverse rear mounted drive shafts. When these joints have been used for front outer drive shaft they have to move in both the vertical and horizontal plane to accommodate both vertical suspension deflection and the swivel pin angular movement to steer the front road wheels.

The compounding of angular working movement of the outer drive shaft steering joint in two planes imposes large and varying working angles even when the torque is being transmitted to the stub axle.
Due to the severe working conditions, special universal joints known as constant velocity joints are employed. These joints have been designed to absorb torque and speed fluctuations and to operate reliably with very little noise and wear having long life.
A smoother and less harsh drive is obtained by incorporating one or more rubber joints in the transmission driveline. Three types of rubber joints in use include moulton, layrub and doughnut.

Figure 14 Universal joint

2.10 BRAKES
Brakes are one of the most important safety features on your vehicle. There are different types of brakes, both between vehicles and within a vehicle. The brakes used to stop a vehicle while driving are known as the service brakes, which are either a disc and drum brake. Vehicles also come equipped with other braking systems, including anti-lock and emergency brakes. 2.10.1 Disc Brakes
Disc brakes consist of a disc brake rotor - which is attached to the wheel - and a caliper, which holds the disc brake pads. Hydraulic pressure from the master cylinder causes the caliper piston to clamp the disc brake rotor between the disc brake pads. This creates friction between the pads and rotor, causing your car to slow down or stop.

Figure 15

2.10.2 Drum Brakes
Drum brakes consist of a brake drum attached to the wheel, a wheel cylinder, brake shoes, and brake return springs. Hydraulic pressure from the master cylinder causes the wheel cylinder to press the brake shoes against the brake drum. This creates friction between the shoes and drum to slow or stop car. Figure 16 Drum brake

2.10.3 Emergency Brakes
Vehicles also come equipped with a secondary braking system, known as emergency, or parking brakes. Emergency brakes are independent of the service brakes, and are not powered by hydraulics. Parking brakes use cables to mechanically apply the brakes (usually the rear brake). There are a few different types of emergency brakes, which include: a stick lever located between the

driver and passenger seats; a pedal located to the left of the floor pedals; or a push button or handle located somewhere near the steering column. Emergency brakes are most often used as a parking brake to help keep a vehicle stationary while parked. And, yes, they are also used in emergency situations, in case the other brake system fails.

2.10.4 Anti-Lock Brakes
Computer-controlled anti-lock braking systems (ABS) is an important safety feature which is equipped on most newer vehicles. When brakes are applied suddenly, ABS prevents the wheels from locking up and the tires from skidding. The system monitors the speed of each wheel and automatically pulses the brake pressure on and off rapidly on any wheels where skidding is detected. This is beneficial for driving on wet and slippery roads. ABS works with the service brakes to decrease stopping distance and increase control and stability of the vehicle during hard braking.

Figure 17 ABS

2.11 STEERING MECHANISM
The steering system converts the rotation of the steering wheel into a swivelling movement of the road wheels in such a way that the steering-wheel rim turns a long way to move the road wheels a short way.
The steering effort passes to the wheels through a system of pivoted joints. These are designed to allow the wheels to move up and down with the suspension without changing the steering angle.
They also ensure that when cornering, the inner front wheel - which has to travel round a tighter curve than the outer one - becomes more sharply angled.The joints must be adjusted very precisely, and even a little looseness in them makes the steering dangerously sloppy and inaccurate.
There are two steering systems in common use - the rack and pinion and the steering box.On large cars, either system may be power assisted to reduce further the effort needed to move it, especially when the car is moving slowly.
2.11.1 RACK AND PINION SYSTEM
At the base of the steering column there is a small pinion (gear wheel) inside a housing. Its teeth mesh with a straight row of teeth on a rack - a long transverse bar. Turning the pinion makes the rack move from side to side. The ends of the rack are coupled to the road wheels by track rods.
This system is simple, with few moving parts to become worn or displaced, so its action is precise. A universal joint in the steering column allows it to connect with the rack without angling the steering wheel awkwardly sideways. Figure 18 Steering mechanism

2.11.2 POWER STEERING
On a heavy car, either the steering is heavy or it is inconveniently low geared - the steering wheel requiring many turns from lock to lock.Heavy gearing can be troublesome when parking in confined spaces. Power-assisted steering overcomes the problem. The engine drives a pump that supplies oil under high pressure to the rack or the steering box.
Valves in the steering rack or box open whenever the driver turns the wheel, allowing oil into the cylinder. The oil works a piston that helps to push the steering in the appropriate direction.As soon as the driver stops turning the wheel, the valve shuts and the pushing action of the piston stops.The power only assists the steering - the steering wheel is still linked to the road wheels in the usual way.
So if the power fails, the driver can still steer but the steering becomes much heavier. 2.12 SILENCER
Silencer works on the principle of destructive interference of sound waves. Inside the silencer, a set of tubes are designed to deliberately reflect sound waves originating from the engine. These reflected waves, interfere and cancel out each other. As a result, the sound from the engine, in drastically reduced. Mufflers are installed within the exhaust system of most internal combustion engines, although the muffler is not designed to serve any primary exhaust function.

The

muffler

is

engineered

as

an acoustic soundproofing device designed to reduce the loudness of the sound pressure created by the engine by way of acoustic quieting. The majority of the sound pressure produced by the engine is emanated out of the vehicle using the same piping used by the silent exhaust gases absorbed by a series of passages and chambers lined with roving fiberglass insulation and/or resonating chambers harmonically tuned to cause destructive interferencewherein opposite sound waves cancel each other out.

Figure 19 Silencer

3 CLASSIFICATION OF CHASSIS
The chassis can be classified on the following basis:
a) According to the fitting of engine
b) According to the number of driving wheels
c) According to the type of frame

3.1 ACCORDING TO THE FITTING OF ENGINE
3.1.1 FULL FORWARD
In full forward chassis, the engine is fitted outside the driver cabin or seat.
Conventionally the engines are fitted at front & drive is given to the wheels from the “rear”. Enough space is available for luggage behind the rear seat. The weight of vehicles is well balance.

Figure 20 Full forward chassis

3.1.2 ENGINE AT CENTER
Here the engine is fitted at the center of the frame. Drive is given to the rear.
This arrangement provide full space of floor for use.

Figure 21 engine at center
3.1.3 ENGINE AT BACK vehicles employing this system is dolphin. Flat floor is available since long propeller shafts are eliminated.With elimination of propeller shaft the center of gravity lowered giving stable driving Better adhesion on road specially when climbing hill.

Figure 22 Engine at back

3.2 ACCORDING TO NUMBER OF DRIVING WHEELS
3.2.1 4 X 2 DRIVE CHASSIS
Describes to a vehicle that has two-wheel drive (2WD) with four wheels.
"4x2" in a 2WD vehicle means there are 4 wheels total and 2 wheels that are driven. The driven wheels can be either back or front wheels but are usually the back wheels. Sport ATVs are typically 4x2.
3.2.2 4X4 DRIVE CHASSIS
Is a vehicle that has four-wheel drive (4WD). "4x4" in a 4WD vehicle means there are 4 wheels total and 4 wheels that are driven. Utility quads are typically 4x4.
3.2.3 6X2 DRIVE CHASSIS
The 6 X 2 tractors configurations also have three axles; however, one of the two rear axles is a non-driving or “dead” axle. The non-driving axle has no internal gearing to provide drive to the wheels of the axle. As a result, there is no internal friction or losses due to lubricant churning, which reduces parasitic losses in the drivetrain.
3.2.4 6X4 DRIVE CHASSIS
A typical three axle Class 8 tractor today is equipped with two rear drive axles and is commonly referred to as a 6 X 4 configuration meaning that it has four-wheel drive capability. 6x4 units are more common in long distance haulage in larger country.

3.3 ACCORDING TO TYPE OF FRAME USED
3.3.1 LADDER CHASSIS
Ladder chassis is considered to be one of the oldest forms of automotive chassis that is still used by most of the SUVs till today. As its name connotes, ladder chassis resembles a shape of a ladder having two longitudinal rails inter linked by several lateral and cross braces. Easier to repair after accidents. This is crucial for taxicabs, because damaged bolt-on fenders can be replaced with the cab returned to earning status immediately, whereas a uni body would require straightening by paid specialists on a machine expensive to rent with the cab laid up for repair longer. Grand-Am allows tubular space frame cars to replace their uni body counterparts, as the cars can easily be repaired with new clips.

Figure 23 Ladder chassis

3.3.2 BACK BONE CHASSIS
Backbone chassis has a rectangular tube like backbone, usually made up of glass fiber that is used for joining front and rear axle together. This type of automotive chassis or automobile chassis is strong and powerful enough to provide support smaller sports car. Backbone chassis is easy to make and cost effective. Standard-conception truck's superstructure has to withstand the torsion twist, and subsequent wear reduces vehicle's lifespan. The half-axles have better contact with ground when operated off the road. This has little importance on roads. The vulnerable parts of drive shaft are covered by thick tube. The whole system is extremely reliable. However, if a problem occurs, repairs are more complicated.

Figure 24 Backbone chassis

3.3.3 MONOCOQUE CHASSIS :
Monocoque Chassis is a one-piece structure that prescribes the overall shape of a vehicle. This type of automotive chassis is manufactured by welding floor pan and other pieces together. Since monocoque chassis is cost effective and suitable for robotized production, most of the vehicles today make use of steel plated monocoque chassis.

Figure 25 Monocoque chassis

4 LOADS ON CHASSIS
4.1 LOADS OF SHORT DURATION
When the vehicle is crossing a broken patch of road, it is acted upon by heavy and suddenly applied loads of short duration. This load results in longitudional direction.

4.2 COMBINED LOADS OF MOMENT ANY DURATION
These loads occur while negotiating curve, applying brakes and striking a pot hole.
4.3 INERTIA LOADS
These loads are applied on the vehicle due to application of brake for short period. This loads tends to bend the side members in the vertical plane.
4.4 IMPACT LOADS
These loads are applied during collision of vehicle with other object. It results in a general collapse.
4.5 LOAD DUE TO ROAD CHAMBER
Load due to road chamber, side wind, and cornering force while taking a turn. It results in lateral bending of side members.
4.6 LOAD DUE TO WHEEL IMPACT
Load due to wheel impact with road obstacles may cause that particular wheel to remain obstructed while the other wheel tend to move forward. It will tend to distrot the frame to paralleogram shape.
4.7 STATIC LOADS
Loads due to chassis parts such as engine, steering, gearbox, fuel tank, body, etc are constantly acting on the frame.
4.8 OVER LOADS
The load of the vehicle which is loaded beyond the specified design load is known as over loads.