[]# Futuretron EV Course_CHAPTER1

# Chapter 1: Automobile Engineering

## 1.1 . Introduction to Automobile Engineering

Automobile engineering involves a study in manufacturing, designing, mechanical mechanisms as well as operations of automobiles. It is an introduction to vehicle engineering which deals with motorcycles, cars, buses, trucks, etc. It includes branch study of mechanical, electronic, software and safety elements. Some of the engineering attributes and disciplines that are of importance to the automotive engineer and many of the other aspects are included in it.

#### History of Automobile

In the early days people used bullock carriage or other animals such as camel, horse etc. to transport good and human from one place to another. In use of these animals one big problem encounter is that they could not travel for long distance and for long time. So the necessary of a machine is arrive which can satisfied these function.

After a great effort of scientists, automobile came into existence in 1769, when a French engineer Captain Nicholas Cugnot designed the first road vehicle propelled by its own power. It is a steam engine automobile but his design proved to be impractical. First steam carriage was built by Richard Trevithick in 1801 in England. In the year 1860, first internal combustion engine was developed by J.J.E. Lenoir. He used coal gas as fuel. There is no compression stroke before burring of fuel. In the year 1867, Nikolaus Otto and Eugen Langer used compression stroke in that engine so the power of engine will increase. In the year 1876, Nikolaus Otto developed first four stroke spark ignition engine.

After this several engineers (Dugald Clerk, James Robson and Karl Benz) developed two stroke engine. In the year 1880, Karl Benz in Germany developed a tricycle propelled by an internal combustion engine. In the year 1892, Rudolf Diesel developed first four stroke compression ignition engine. In the year 1920 a stratified charge engine developed which can run on both petrol and diesel.

**Working Principle**

An Automobile is a self-propelled vehicle with a primary function to transport people and goods from one place to another. An Automobile engineering stream deals with various types of vehicles, their working principles and applications.

An automobile runs on the principle of conversion of energy. The chemical energy of gasoline is burnt under a controlled pressure converting it to linear kinetic energy. The linear motion is then converted into rotary motion using vehicle transmissions that propel the vehicle.

**Types of Automobiles**

* Load-carrying capacity: HTV, LTV, LMV.
* Wheel basis: Two, Three, Four, Six wheeler vehicle.
* Fuel used basis: Petrol, Diesel, CNG and Electric.
* Other basis like body and transmission type.

## 1.2 Basic Components of the Automobile

* Chassis and Frame: It supports the structure of vehicle holding engine, body, wheels, etc
* Power source: IC engine or Electric motor which generates power for the automobile.
* Transmission: To transmit power developed by the engine to wheels.
* Braking system: To slow down the vehicle.
* Suspension system: To absorb shocks and vibrations on the road.

### 1.2.1 Frame and Chassis

### Vehicle Frame
A vehicle frame, also known as its chassis, is the primary motor vehicle support system to which all other parts are connected, similar to an organism's skeleton.
Practically every car had a structural frame removed from its body until the 1930's. This design is known as body-on-frame construction. Nearly all passenger cars have, over time, converted to unibody construction, meaning that their frame and bodywork have been merged into one another. All trucks, buses, and most pickups are currently still using a separate frame as their chassis.

#### Functions
The main functions of a frame in motor vehicles are:
• To support the vehicle's mechanical components and body
• To deal with static and dynamic loads, without undue deflection or distortion.

#### Types
• Ladder type frame
• X-Type frame
• Perimeter frame
• Platform frame
• Space Frame

#### Ladder type frame

credits: https://carbiketech.com/chassis/

The ladder frame is named for its resemblance to a ladder, which is one of the simplest and oldest of all designs. It consists of two symmetrical beams, rods, or channels that run the vehicle's length, and several transverse cross-members that link them. Originally used on almost all vehicles, the ladder frame in favour of perimeter frames and unitized body construction was slowly phased out on cars. It is now largely seen on trucks. Because of its continuous rails from front to rear, this design offers good beam resistance but poor resistance to torsion or warping when using simple, perpendicular cross-members. The average height of the vehicle would be higher due to the floor pan being above the frame, rather than inside.

#### X type frame

credits: https://www.slideshare.net/shaikusmanshag/2frame

This is the design used for General Motors' full-size American models in the late 1950s and early 1960s, in which the rails from alongside the engine seemed to cross in the passenger compartment, each continuing at the extreme rear of the vehicle to the opposite end of the crossmember. This was deliberately chosen to decrease the total height of the vehicles because of the increase in the size of the humps for the transmission and the shaft humps for the propeller, as each row still had to cover frame rails. Some models had the differential positioned not by the normal bar between axle and frame, but by a ball joint on top of the differential attached to a socket in a desire bone holding onto a frame brace.
Reportedly, the X-frame improved on previous designs, but lacked side rails and therefore did not provide adequate side-impact and collision protection. This style was replaced by frames with perimeters.

#### Perimeter frame

credits: https://www.artmorrison.com/frames.php

Similar to a ladder frame but just behind the rocker and sill panels, the middle sections of the frame rails sit outboard of the front and rear rails. This was done to allow a lower floor pan, particularly at the passenger footwells, to lower the seating height of the passengers and thus the overall height of the vehicle in passenger cars. It allowed to increase sales for annual model changes introduced in the 1950s, but without costly structural changes. There are no perimeter frame cars sold in the U.S. as of 2014 after the Ford Motor Company phased out the Panther model in 2011, which ended the perimeter frame passenger car in the U.S. The perimeter frame, in addition to a lowered roof, allows lower seating positions when necessary and offers greater protection in the event of side effect.

#### Platform frame

credits: https://www.wikiwand.com/en/Front_mid-engine,_front-wheel-drive_layout

It is a redesign of the perimeter frame, or backbone framework, in which the floor of the passenger cabin, and often even the floor of the luggage compartment, is incorporated into the structure as load-bearing sections for additional strength and stiffness. No floor parts are simply sheet metal straight off the plate, but for extra strength, they were stamped with ridges and hollows.
Many popular European cars employed platform chassis. The most well-known of these is the Volkswagen Beetle, on which the pan-building body is named. The German example of this is the 1950s and 1960s Mercedes-Benz "Ponton" cars.

#### Space frame

credits: https://www.pinterest.com/pin/471118811013136229/

The suspension, engine, and body panels are attached in a (tubular) spaceframe chassis to a three-dimensional tube skeleton frame, and the body panels have little or no structural function. The geometry allows full use of triangles to optimize rigidity and minimize weight and all the forces in each strut are either tensile or compressive, never bending, so they can be held as thin as possible.

### Material used for chassis and frame

#### Steel

Steel stands for manufacturers with all the necessary features as the first choice. The steel industry progress made the steel stronger, lighter and stiffer than the previous ones. Steel not only includes vehicle bodies but also engines, frames, wheels and many other parts. Iron and steel produce vital structural components for bulk vehicle manufacturing and are low-cost. The best reason to use steel as a body structure is its inherent ability to absorb the energy from impact generated in a crash.

#### Aluminium

For the automotive industry, aluminium is commonly used in frame and body construction. The use of aluminium can decrease the vehicle's weight. The low weight and high variable energy absorption and reliable resistance are its most significant characteristics. Aluminium is corrosion resistant but cannot replace steel parts due to its low flexibility modulus. Those parts therefore need to be re-engineered in order to adopt the same mechanical strength.
Latest innovations showed that by replacing steel with aluminium, 50% of the steel is saved in weight for the body. It will result in a decrease of the vehicle's overall weight by up to 20-30 per cent.

#### Carbon fibre

Because of its low density, high strength, high rigidity and strong resistance to creep and corrosion, carbon fibre composite materials (CFRP) are suitable lightweight materials for automobiles. Today, in different areas such as vehicle bodies, tail planes, car frames, hoods and automobile interiors, we will find carbon fibre composite materials. In addition to safety, lightweight is the main advantage of carbon fibre composites, and weight reduction is another significant advantage of carbon fibre composite. The immediate effect of the light weighting is a decrease in car fuel consumption.

For further explanation on types of Automobile chassis, please refer - https://youtu.be/n1cTMnNn-XI

## 1.2.2 Engine
A motor or an engine is a system that is designed to transform one source of energy into mechanical energy. The petrol engine and the diesel engine are both the internal combustion engines which are used in modern automobiles. Through combustion, the fuel’s chemical energy is transformed into heat energy, and some of that heat energy is converted into mechanical energy by the engine.

Combustion is also known as burning, describes the basic method of extracting energy from combination of fuel and air. The ignition process and combustion process of the fuel occurs inside the engine itself in an Internal Combustion Engines. Therefore, the engine partly transforms the energy from the combustion into motion. The piston is pushed by the increasing combustion gases, which rotates the crankshaft. Ultimately, the motion drives the wheels of the vehicle through a set of gears in the powertrain.

There are currently two types of internal combustion engines in production that is the gasoline engine with spark ignition and the diesel engine with the compression ignition. Most of these four-stroke cycle engines, that is four piston strokes to complete a cycle. There are four distinct phases in the cycle: intake, combustion, compression and power stroke, and exhaust.

### Working of 4-stroke Engine

The 4 strokes of power cycle are Intake stroke, Compression stroke, Power stroke, Exhaust stroke.

source: https://projectmech.com/four-stroke-engine-working-principle/

Intake stroke: Also called suction stroke. The exhaust valve is closed and the intake valve is open, air is drawn inside the cylinder. To achieve the optimal air-fuel ratio the fuel injector sprays the fuel inside the cylinder. The piston’s downward motion allows air and fuel to draw into the cylinder.By the end of intake stroke, the intake-valve shuts.

Compression stroke: Intake and exhaust valves are closed, this isolates the combustion chamber from the ambient air. The piston’s upward motion allows the air-fuel mixture to be compressed upwards against the spark plug. This compression makes the mixture of fuel and air unstable making ignition simpler.

Power stroke: Also known as Combustion stroke. Both intake and exhaust valves remain closed. The spark plug produces a spark that ignites the mixture of compressed air and fuel. The resultant combustion energies vigorously drive down the piston. This downward movement of the piston provides positive driving energy to move the vehicle. This driving energy provides positive linear displacement. This linear displacement is converted into rotary motion by using a crankshaft connected to the piston rod. Power from crankshaft is transmitted to the wheels by using set of transmissions.

Exhaust stroke: This is the last cycle. Combustion of fuel produces residue gases having very high temperature and pressure. Intake valve remains closed and exhaust valve opens and the exhaust gases are forced up by the upward motion of the piston and hence smooth disposal of the gases into the exhaust port.

Spark gasoline ignition and diesel compression ignition engines differ in the way they deliver and ignite the fuel. The fuel is further mixed with air in the spark ignition engine, and then induced into the cylinder during the process of intake. After the mixture of fuel-air is compressed by the piston, the spark ignites it which causes combustion. The increase in the combustion gases during the process of power stroke, drives the piston. In case of diesel engine, just air is induced into the engine and then it is compressed. The diesel engines then spray the fuel at a suitable calculated rate into the hot compressed air which causes it to ignite.

### 1.2.3 Braking System

In any automobile, the main role of the braking system is to control the vehicle as it descends along the hilly areas, to safely stop the vehicle in the shortest possible time in case of emergency, to put the vehicle to rest. Breaking system in an automobile is an assembly of various connections and components such as brake lines or mechanical links, brake disc or brake drum, master cylinder or the fulcrums etc., arranged in such a way that it transforms the kinetic energy of the vehicle into heat energy which in turn stops or deaccelerates the
vehicle.

#### TYPES OF BRAKING SYSTEM:

1. **Based on Power Source:** In this system the pedal force which is applied by the driver on brake pedal to the final brake drum/disc in order to stop or deaccelerate the vehicle.
It is of 6 types:
• Mechanical Braking System: The brake force applied is transferred through various mechanical linkages such as cylindrical rods, springs, fulcrums, etc. This type of braking system was used in old models and they are outdated currently due to their less effectiveness and performance
• Hydraulic Braking System: Brake fluids are used instead of mechanical linkages to deaccelerate or stop the vehicle. Due to its high brake force generating capacity and high efficiency, almost all the bikes and cars on road today are equipped with hydraulic braking system.
• Air/Pneumatic Braking System: Hydraulic Brakes have more than enough breaking power to stop/deaccelerate the vehicle, but the reliability of the hydraulic braking system is a major concern when it comes to heavy vehicles that are larger in size. In air braking system the atmospheric air is used to transfer the brake pedal to the final drum/disc through compressors or valves. High end cars and heavy-duty vehicles use air brake system due to its effectiveness and fail proof capability.
• Vacuum Braking System: This is the traditional type of braking system in which vacuum within the brake lines allows the brake pads to move and end up stopping or deaccelerating the vehicle in turn. They are cheaper than air braking system but less safe compared to air brakes.
• Magnetic Braking System: It is a friction less braking system were the magnetic fields produced by the permanent magnets used in this type of braking system to enable the braking of the vehicle. This is the cutting-edge technology which requires no pressure to cause braking and compared to other braking system the braking response is very quick.
• Electric Braking System: This is used in Electric Vehicles where braking is provided by the electric motors, the key source of electricity in electric vehicles. The types are Plugging Brakes, Regenerative Braking System and Dynamic or Rheostat Braking.

2. **Based on Fictional Braking Contact:** The braking system is of 2 types based on the final friction interaction between the components of the rotating brake i.e. brake drum or disk rotor and brake shoe.
• Internal Expanding Brakes (Drum Brakes): It is the traditional brake in which a collection of pads or shoes that press against a rotating drum shaped part called a brake drum that causes the friction.
• External Contracting Brakes (Disc Brakes): Disc brakes use the force applied to wheel-attached discs to slow down or stop a vehicle.

3. **On the basis of application:** Based on the method of applying brakes
• Foot/Service Brakes: foot operated brakes are used in cars and the combination of foot and pedal operated are used in bikes.
• Hand/Parking Brakes: It is the emergency brake as it is independent of the main service brake, it consists of hand operated brake lever that is connected through the metallic cable to the brake drum or disc rotor.

4. **Based on Brake Force Distribution**
• Single Acting Brakes: Braking force is transferred either to a pair of wheels(4wheeler) or to a single wheel(2wheeler) by means of single actuator.
• Dual Acting Brakes: Here dual actuator mechanism is used. It is used in all 4-wheel cars and trucks.

### 1.2.4 Suspension System

Suspension is the term given to the system of springs, shocks absorbers and linkages which link a vehicle to its wheels.This acts as a dual purpose, helping to carry and improve the stability of the vehicle. Suspension protects and defends the body and any load or cargo from injury and tear.
Source: https://www.kylinmotors.com/wp-content/uploads/2016/04/suspension-repair.jpg

#### Purpose of suspension system

1.Offers smooth ride
2.Insures weight support
3.Enables fast cornering without intense body rolling
4.Holds the tires firmly in contact with the road
5.Lets front wheels turn side by side while steering
6.Works with a steering mechanism to keep the wheels balanced correctly
7.Isolate passengers and freight from vibration and shock

Video Link: https://youtu.be/DKql4Is8Pas

#### Types of Suspension Systems

Suspension systems are divided into three categories

* Dependent
* Semi Independent and
* Independent suspension system.

#### Dependent suspension systems

The network of linkages used to locate them that distinguish dependent systems, both longitudinal direction and transversally. Both functions are often merged in a series of linkages.
Both wheels on the same axle are rigidly attached to the same suspension mechanism in this type on suspension system. The force acting on one wheel impact another wheel's motion. The key benefit of this type of suspension system is greater than other types of suspension system, the weight carrying ability of it. Therefore this type of suspension is mostly used in heavy duty vehicles such as trucks, buses and commercial vehicles.

**Leaf springs**

Source: https://i.imgur.com/nTVbBv2.jpg

It takes the shape of an arc-shaped length of rectangular cross-section spring steel. The center of the arc provides location for the axle in the most common configuration, while loops formed on either end provide for connection to the chassis of the vehicle.

A leaf spring can be either attached directly to the frame at both ends, or directly connected to one end, normally the front, with a short swinging arm attached to the other end via a shackle. The shackle takes up the leaf spring 's tendency to elongate when compressed and thus makes it shock absorbent.

This ensures a constant camber, dependent suspension is most common in vehicles which have to bear large loads as a proportion of vehicle weight, have relatively soft springs and do not use active suspensions. The use of dependent front suspension has restricted itself to heavier commercial vehicles.

#### Semi Independent suspension system

In a semi-independent suspension, an axle 's wheels can shift relative to each other as in an independent suspension because one wheel 's position has an influence on the other wheel's location and attitude. This effect is achieved by twisting or deflecting the load-bearing suspension sections. torsion bar is the most common form of semi-independent suspension.

The torsion bar is essentially a metal rod length attached at one end of the car frame, and the lower connection at the other end of the suspension. As the wheel passes the bar twists over a bump. When the bump is passed it returns to its original position, restoring the car to its normal drive height. The bar's resistance to twisting has the same effect as the spring used in more standard suspension systems. To maintain the ride height of the car a certain amount of load is applied permanently to the bar. In the system, the torsion bar can either be mounted longitudinally or transversally. One of the most useful aspects in this device is the adjustable torsion bars.

Source: https://encrypted-tbn0.gstatic.com/images?q=tbn%3AANd9GcTq-H9BQRRWfo-d6Uy_1h2jAZhXKUAvl74KJA&usqp=CAU

#### Independent suspension System

in this type of suspension system Both wheels of the same axle connected to separate suspension system  so the force acting on one wheel does not impact the movement of another wheel. Compared with dependent suspension system, this type of suspension system provides more comfort. It provides improved handling and comfort for riding so it is used in cars and Volvo bus etc.

**Types of independent suspension systems :**

* MacPherson strut/Chapman strut
https://i.pinimg.com/736x/a7/b7/b1/a7b7b12838023b83cf0e2359bce8f97b.jpg

* Upper and lower A-arm (double wishbone)
https://www.moogparts.eu/content/dam/marketing/emea/moog/blog/double-suspension-wishbone.png

* Multi-link suspension
https://img.favpng.com/0/16/23/car-audi-multi-link-suspension-control-arm-png-favpng-W0Li4acMXp41YyH8hwk9FqxMp.jpg

* Semi-trailing arm suspension
https://qph.fs.quoracdn.net/main-qimg-b49df0edf46a0598778a42a54027a91f

* Transverse leaf spring
https://www.howacarworks.com/illustration/1341/checking-a-transverse-leaf-spring-for-wear.png

#### Suspension Components

There are three basic types of suspension components: linkages, springs, and
shock absorbers.

**Links:** The linkages are the bars and brackets that aid the wheels, springs and shock absorbers. There are a variety of varying shaped links that are used by the different forms of suspension systems. They range from straight bars to crafted, cast, or stamped metal forms that fit better on vehicle frames or body frameworks to support the springs, shocks, and wheels. The shortest linkage is a straight bar on the opposite side of the vehicle, linking one wheel to the other. As explained later, some can be intricately designed to link springs, shock absorbers, and wheels to automobiles.

**Springs:** Springs support the vehicle by dampening the shock loads in the roadway such as bumps and gaps. There are generally three types of springs used in suspension systems: coil, leaf and torsion bar. Coil springs are merely wound torsion bars.
They are widely used because they are compact, easy to install and have
Excellent properties for life durability. Leaf springs are long , thin members loaded in bending. They are used as an assembly consisting of many thin metal layers to achieve the proper spring rate. Leaf springs act as both the part of the damping and linkage.Torsion bars depend on a long bar twist to provide a spring rate to dampen the loading of car shocks. Torsion bars mount over a vehicle's exterior and are more difficult to carry than others.

**Shock Absorbers:** Shock absorbers use hydraulic pistons and cylinders to cushion also the vehicle from shock loads. They also serve to dampen spring oscillations, thus bring the vehicle back to a neutral position soon after being shock loaded by a road obstruction. Shock absorbers use a piston and cylinder along with adjustable valves to control the flow of hydraulic fluid to set the damping force in both the retract (jounce) and extend (rebound) positions. Shock absorbers are set to retract under a lower force than to extend. This action absorbs road bump forces
and dampens spring oscillations resulting in better vehicle ride and control.

#### The basic components of a suspension system are as follows

* **CONTROL ARM** : A movable lever that fastens the steering knuckle to the vehicle frame or body).
* **CONTROL ARM BUSHING** : A sleeve, which allows the control arm to move up and down on the frame.
* **STRUT ROD** : Prevents the control arm from swinging to the front or rear of the vehicle.
* **BALL JOINTS** : A swivel joint that allows the control arm and steering knuckle to move up and down, as well as side to side.
* **SHOCK ABSORBER or STRUT** : Keeps the suspension from continuing to bounce after spring compression and extension.
* **STABILIZER BAR** : Limits body roll of the vehicle during cornering.
* **SPRING** : Supports the weight of the vehicle; permits the control arm and wheel to move up and down.

## 1.3 Parameters in automobile ride and handling

### Centre of Gravity

The Centre of gravity plays an important role in vehicle dynamics. CG is a point at which a system or body behaves as if all its mass were centered at that point. Where the weight, and also all accelerative forces of acceleration, braking, and cornering act through it. When analyzing the forces applied to the car, the CG is the point to place the car weight, and the centrifugal forces when the car is turning or when accelerating or decelerating. Any force that acts through the CG does not tend to make the car rotate.
The center of mass height, relative to the track, determines load transfer from side to side and causes body lean. When tires of a vehicle provide a centripetal force to pull it around a turn, the momentum of the vehicle actuates load transfer in a direction going from the vehicle's current position to a point on a path tangent to the vehicle's path. This load transfer presents itself in the form of body lean. Body lean can be controlled by lowering the center of weight or widening the car track, it can also be controlled by the springs, anti-roll bars, or the roll center heights.

source: https://tse3.mm.bing.net/th?id=OIP.uEQh7grHFtDEyFPGsPXtVQHaHa&pid=Api&P=0&w=300&h=300

To calculate the CG point we consider the hub heights( RF, RR), and weighing the car on level ground (W). Knowing the wheelbase (ℓ) and weight distribution, we can calculate the longitudinal location (a and b) of the center of gravity (CG). Then we lift the vehicle to set the rear wheels onto platforms and weigh the front axle (WF) in this tilted position. The angle (θ) can be computed using the triangle formed by the wheelbase and the height the rear wheels are raised. Plugging all of this into the following formula spits out CG height:


The ride comfort of a vehicle depends on the static deflection of suspension spring. Static deflection is the rate at which the suspension compresses in response to weight. The rate of static defection with time is a natural frequency of a suspension which can be determined by a simple formula expressed as follows:


NF = Natural Frequency in Cycles Per Minute (divided by 60=Hz).
SD = Static Deflection in Inches.

### 1.4 Cornering Dynamics

According to Newton’s First Law, a moving body will continue moving in a straight line until it is acted upon by a disturbing force. Newton’s Second Law refers to the balance that exists between the disturbing force and the reaction of the moving body. In the case of the automobile, whether the disturbing force is in the form of an incline in the roadway, or the cornering forces produced by tires, the force causing the turn and the force resisting the turn will always be in balance.

In a turn, angular acceleration results in a force that is centered at the vehicle center of gravity and acts in a direction away from the turn center. The ability to overcome these forces and produce a controlled, stable turn depends upon the combined characteristics of the suspension and tires. The job of the suspension system is to support, turn, tilt and otherwise manage the tires and their relationship to the vehicle and the ground in a way that will maximize their capabilities.

At relatively low speeds the vehicle turns according to the geometric alignment of the wheels. The wheels roll in the direction they are heading, and the vehicle turns about the point established by a projection of the front axles intersecting a projection of the rear axle. As speed increases, the actual turn center moves forward due to the slip angle of the tires.

source: https://tse3.mm.bing.net/th?id=OIP.wwKcvbhIqfcNAfINunXGpwHaC0&pid=Api&P=0&w=481&h=184

## 1.5 Oversteer and Understeer

The weight bias of the vehicle determines its inherent oversteer and understeer characteristics. A vehicle that is heavier at the front will tend to understeer and one that is heavier at the rear will oversteer. A vehicle in which the weight is equally distributed between the front and rear axles tends to exhibit neutral steer characteristics. Although the inherent understeer and oversteer characteristics of a vehicle are determined by its weight distribution, the design of the suspension and the selection of wheel and tire size can enhance or moderate those characteristics.

Understeer and oversteer do not occur under normal conditions and such behaviour is observed under certain conditions and around curves. Understeer generally occurs when the front tyres start slipping while you go around the curve. The slip occurs due to great amount of lateral acceleration that car is experiencing while tyres are simultaneously handling the engine torque or braking force. This generally overwhelms the tyres and causes understeer.
Oversteer generally occurs in case the rear wheel drive cars, where the power applied to the rear wheels exceed than what they can handle and this makes the rear spin out of the intended driving curve. Oversteer can also occur when you brake hard or if you suddenly remove your foot from the accelerator.

source: https://tse1.mm.bing.net/th?id=OIP.aoIXFWFBHI9nBESBt9IeaQHaC3&pid=Api&P=0&w=443&h=172

In case of understeer, the behaviour can be easily corrected by taking your foot off the accelerator pedal as this transfers some weight to the front wheels and increases available traction. Since this is the most natural reaction car that understeer are considered easier to drive. Oversteer is generally not easy to recover from and can be really dangerous though it requires the same reaction, easing the throttle gently and brake input. The behaviour is greatly affected by rainy weather and tyres condition and pressure.

### 1.6 Rollover threshold

At the most fundamental level, a vehicle’s rollover threshold is established by the simple relationship between the height of the center of gravity and the maximum lateral forces capable of being transferred by the tires.

Modern tires can develop a friction coefficient as high as 0.8, which means that the vehicle can negotiate turns that produce lateral forces equal to 80 percent of its own weight (0.8 g) before the tires loose adhesion. As long as the side-force capability of the tires is less than the side-force required for overturn, the vehicle will slide before it overturns.

Rapid onset turns impart a roll acceleration to the body that can cause the body to overshoot its steady-state roll angle. This happens with sudden steering inputs, it occurs when a skidding vehicle suddenly regains traction and begins to turn again, and it occurs when a hard turn in one direction is followed by an equally hard turn in the opposite direction (slalom turns). The vehicle’s roll moment depends on the vertical displacement of the center of gravity above its roll center.

Source: https://tse3.mm.bing.net/th?id=OIP.zT0GEfXefIMcpFP&pid&P=0&w=218&h=155

Overshooting the steady-state roll angle can lift the inside wheels off the ground, even though the vehicle has a high static margin of safety against rollover. Once lift-off occurs, the vehicle’s resistance to rollover rapidly diminishes, which results in a condition that quickly becomes irretrievable.

The roll moment of inertia reaches much greater values during slalom turns wherein the forces of suspension rebound and the opposing turn combine to throw the body through its roll limits from one extreme to the other. The inertial forces involved in overshooting the steady-state roll angle can exceed those produced by the turn-rate itself.

Tripping is another cause of rollover in an otherwise rollover-resistant vehicle. Tripping occurs when a vehicle skids against an obstacle, such as a curb. In this case, the lateral speed of the vehicle is suddenly arrested and extremely high momentary loads are imposed across the vehicle’s center of gravity. If the load spike exceeds the vehicle’s rollover threshold, rollover will occur.