Unit-III:Vehicles and their Specifications 

Classification of automobile. Vehicle specifications of two/three wheeler, light motor vehicles, trucks, buses and multi-axle vehicles. Engine components (Introduction). Study of engine specifications, comparison of specifications of vehicles. Introduction of Electric and Hybrid Vehicles. Cost analysis of the Vehicle.

Introduction to Automobiles

Common Specification Terminology

A.Dimensional Attributes

A.1 Length

"This defines the length of the car from end to end. it is commonly denoted in millimetres ". 

The length of the car majorly affects the handling and stability.  As the length increases the straight line stability of the car goes up but the cornering agility decreases. Keep in mind, more length need not necessarily translate to leg room on the interior

A.2 Width

Tthe width simply denotes the dimensions of the car measured cross-sectionally. Unlike the length, more width does translate to more cabin room and more comfortable seating, especially for the rear passengers. Apart from that increasing the width also increases the straight line stability similar to the length. More width also means more frontal area which increases the level of air resistance thus decreasing the overall top speed.

 It is also denoted in millimetres and the spec sheet will usually specify if the mirrors are included in the measurement.

A.3 Height

The height of the car is defined as the height measured from its lowest point (i.e. the point where the tyres touch the road) to the tallest point on the car’s roof. Leaving aside the headroom, the height of the car has a direct effect on the car’s handling. A taller car will have a higher centre of gravity, lesser down-force and will experience more body-roll. Due to this, a taller car will feel very unsettled when pushed through corners. This is why all sports cars have low-slung body constructions which make them very agile through turns.

A.4 Wheelbase

Now we commence with the more technical terms seen on the car spec sheet. The wheelbase is defined as the distance between the centres of the car’s front wheel and rear wheel. Unlike the length, the wheelbase can be used as an indicator for interior room. A car with a longer wheelbase will feel more planted on straight roads but will move slower through the turns. Shorter wheelbase cars will have quicker handling but won’t feel as firm-footed on the straights. The wheelbase influences these factors since it has a direct effect on turning radius which we will understand in the next point.

B. Engine Terminologies

Engine Configuration

Now we move on to the car spec sheet terms pertaining to the heart of your vehicle, the engine. The first aspect we will discuss here is the engine configuration. The configuration broadly describes the layout and orientation of the primary components present in the engine.  It is mostly divided into three attributes namely:

B.1 Number of Cylinders 

This refers to the number of combustion chambers present inside the engine. A majority of the cars in India are either 3-cylinder or 4-cylinder engines. 4 cylinder engines are smoother, have better performance and usually cost more. 3 cylinder engines are more fuel efficient, have lower running costs but aren’t as refined as 4 cylinder engines.

B.2 Number of Valves 

The number of valves refers to the number of openings present on the top of each cylinder to induce air or remove exhaust gases. Nowadays almost all cars come with a 4 valve arrangement (2 for intake and 2 for exhaust). In the previous decade, 2 valve configurations were very popular but have been replaced almost entirely by their modern 4 valve counterparts. A few high-performance cars come with 5-valve (3 intake and 2 exhaust) engines as well.

B.3 Valvetrain Type 

The Valvetrain refers to the orientation of the camshafts present inside the engine head.

They are of two types, SOHC( Single Overhead Camshaft) and DOHC (Dual Overhead Camshafts). 

In the case of an SOHC valvetrain, a single camshaft is used to actuate both the intake and exhaust valves. This is achieved with the help of rocker arms linked to the valves on either side of the camshaft. 

A DOHC valvetrain contains two camshafts, one for the intake valves and one for the exhaust valves. In general, a DOHC arrangement is more superior to the SOHC arrangement. With a DOHC, the contact is directly between the cam and valves which increases precision, proper timing and performance as well. 

B.5 Displacement

In physical terms, the engine displacement simply refers to the total available volume in the engine cylinders. It is the summation of the individual air volume of each combustion chamber. It is measured in cubic centimetres or cubic capacity (cc) as we commonly know. The displacement has a very direct effect on the performance of your car. More displacement means more space for the engine to burn fuel which in turn gives more performance. Lesser displacement engines draw in a lesser quantity of fuel which means lesser performance but better fuel efficiency. Displacement is sometimes listed on the car spec sheet in terms of litres (1000cc = 1 litre).

B.6 Max Torque

Torque is defined as the total rotational force being exerted by the engine on the wheels of your car. Max torque refers to the maximum amount of torque that can be produced by the engine. This peak value is developed only at a certain RPM so it is usually mentioned as “X” Nm at “Y” RPM (eg- 233Nm at 3400RPM). The torque defines the pulling capacity and versatility of the engine’s powerband.  More torque means the engine operates at lower RPM and has great pulling power regardless of the RPM you are in.

Hence you won’t have to perform frequent downshifts to stay in the correct powerband. The high torque present will allow the car to accelerate comfortably with its pulling power even if you are a gear or two higher. This is why diesel powered cars or SUVs are better suited for highway driving and long runs. Torque-packed cars generally prefer the lower end of the RPM range. Torque is measured in Nm or Newton-Metres.

B.7 Max Power

Power is the sister function of torque. Power and torque the two primary parameters measuring engine performance on the car spec sheet. Technically speaking, power and torque are both derived from the same process. Power is equal to (Torque*RPM)/5252. Max power is again the maximum amount of power that the engine is capable of producing at a certain RPM. When we are talking power we are talking performance.

Engines designed to put out high levels of power are the ones which have high top speed, high acceleration and give that gut-wrenching sense of adrenaline. They might not be very good with the pulling capacity and could very well struggle with a lot of luggage or many occupants. But under normal conditions, a car with more power will always run faster. Such cars will feel at home in the upper end of the RPM range and not so much in the lower end. Power is measured in BHP or Brake Horse Power.

B.9 Drivetrain Type

The system that transfers power from the gearbox to the car axles is referred to as the drivetrain. There are 4 common types of drivetrains available in today’s market namely, Front Wheel Drive (FWD), Rear Wheel Drive (RWD), All Wheel Drive (AWD) and 4-Wheel Drive (4WD). Here AWD and 4WD are the confusing terms since in both cases power is transferred to all 4 wheels. The difference here is that AWD is locked into this mode all the time. 4WD is more commonly offered on rugged SUVs and has to be toggled by the user. In case you find yourself in a stuck in mud or slush while off-roading, you can switch into the 4WD mode to help you get out of it.

B.10 Transmission (Type and Speed)

Your car’s transmission or gearbox as it is commonly known is one of the most important components in the engine. The gearbox is of two primary types, automatic and manual as most of you are probably familiar with. The Speed number of the gearbox denotes the number of gears available to shift into (e.g. a 4-Speed gearbox means the car has 4 gears). The only exceptional case here is the CVT type automatic transmission. A CVT has infinitely variable gears and no defined fixed gear ratio. This is the same type of transmission used on the majority of the automatic scooters as well

C. Chassis Terminologies

Front Suspension

For the final section of this article, we start with the car spec sheet terms pertaining to the chassis section. The front suspension denotes the type of spring and control arm arrangement present on the front wheels of the car. The most commonly used front suspension arrangement is the MacPherson Strut.

Rear Suspension

The rear suspension denotes the type of spring and control arrangement present on the rear wheels of the car. The most popular configuration here is the Torsion Beam type.

Tyre Size

The Tyre size simply denotes the dimensions of the tyre. However, understanding what the dimension means is something that not a lot of people know. Usually, the size is denoted in this format, “Tyre Width in mm/Aspect Ratio-Rim Diameter in inches”. So if the size says 245/55-R15, this means the tyre has a width of 245 mm. The aspect ratio of 55% means that 55% of the width is used up as the side wall. R-15 means the steel/alloy rim has a diameter of 15 inches.

Brakes (Type and Size)

Finally, we reach the last characteristic on our list of car spec sheet terms. The brakes section denotes the type and size of the brakes used in the car. Brake types are divided into two broad categories, drum, and disc. Drum brakes are the basic types which are only found on the lower variants of C-segment and below vehicles only. Over the past 8-10 years, the more technologically advanced disc brakes have increasingly taken over their primitive counterparts and should replace them altogether soon. The size of the brake is measured through its diameter. The larger the diameter, the more the stopping power you have.

Types of Vehicles – Car Body Styles

1. Microcar

These are tiny cars that often come with an engine size of less than one liter and 700c. They come in various unusual designs and are ideal for city traffic due to their fuel efficiency and parking ease.

The microcar is most often a two-passenger vehicle. Examples of microcars include cyclecars, bubble cars, and the Tata Nano car. Modern microcars are most often electrically powered.

2. Sedan

A sedan has four doors and a separate boot. The difference between a hatchback and a sedan is that the rear trunk door does not include the rear window. The door hinges are installed under the window.

Sedan cars are often quite limited of space in the trunk, but they often have a little bit sportier look if you are looking for it.

they're available in a range of sizes from small (subcompact vehicles like Nissan Versa and Kia Rio) to compacts (Honda Civic, Toyota Corolla) to mid-size (Honda Accord, Nissan Altima), and full-size (Toyota Avalon, Dodge Charger). Luxury brands like Mercedes-Benz and Lexus have sedans in similar sizes as well. 

3. CUV (Crossover)

A crossover is often confused with an SUV. The crossover is a light off-road car with some SUV features. A crossover does often come with a two-wheel drive but can also come with 4-wheel-drive. It is basically an off-road car chassis but more built for city traffic.

A key differentiating factor is a chassis – the crossover uses a light monochrome while the SUV utilizes a ladder frame chassis. Basically, it means that a CUV shares the frame of a car, and the SUV shares the frame of a truck. It can often be referred to as a mix of an SUV and a hatchback.

4. SPORT-UTILITY VEHICLE(SUV)

The SUV is a large car that can carry five to seven passengers. They are basically the same as a crossover, except they are built on a body-on-frame chassis. They are often 4wd and have good off-road capabilities.

They often come armed with the latest electronics and are very comfortable to ride in. They also often come with off-road accessories like enhanced suspension and large wheels. 

You can have SUVs in varying sizes – compact, mid-size, and full-size. 

A good example of an SUV is the range rover, Jeep Cherokee or Suzuki Vitara. Sizes start at subcompact (Hyundai Kona, Nissan Kicks), mid-size, and go all the way to full-size (Ford Expedition, Chevrolet Tahoe). Luxury brands offer many SUV models in most of the same size categories. 

5. Hatchback

A Hatchback car is basically a mix of a sedan and a combi car. They often come in a 5 door setup and have a trunk door that opens upward. Like the combi, a hatchback has door hinges above the rear window. The difference between a combi and a hatchback is often the size and the fact that the combi often has a much steeper angle on the trunk door. The Volkswagen Golf and Kia Rio are two typical hatchbacks. More recently, rear hatches have found their way on to some larger cars, like the Audi A7 and Kia Stinger. They look like sedans, but they actually have a steeply raked hatchback that affords easier accessibility to the cargo area and greater carrying capacity than a traditional trunk would. 

6. Station Wagon

A Station Wagon is not a very common car model type, but they do absolutely exist. They are basically a combi car, but they are often very long with more angle on the trunk.

A good example of a station wagon is the volvo v90.

7. Pickup

Pickup cars have become very common in recent years. A pickup has an enclosed cab with an open cargo area. They can either be two passengers or four.

Pickups are ideal for farmers and transporting goods due to their large cargo areas. They do come in both 2WD and 4WD.Currently, pickup trucks come in two size categories: full-size and mid-size.

BEST NEW TRUCKS

8. Van

A Van is a two or three seated car model that is often used to transport goods. They often have a sealed cabin from the cargo area. They most often do not have windows to the cargo area, but there are glass windows at the rear doors in some models.

9. Coupe

A coupe car is basically a sedan but with two doors instead of four. Coupe cars often have a back seat for two or three more passengers, but you often have to fold any of the front seats to get there. A little bit of sportier car models mostly uses coupe cars

A coupe has historically been considered a two-door car with a trunk and a solid roof. This would include cars like a Ford Mustang or Audi A5—or even two-seat sports cars like the Chevrolet Corvette and Porsche Boxster. Recently, however, car companies have started to apply the word "coupe" to four-door cars or crossovers with low, sleek rooflines that they deem "coupe-like." This includes vehicles as disparate as a Mercedes-Benz CLS sedan and BMW X6 SUV. At Car and Driver, we still consider a coupe to be a two-door car. 

10. Mini Truck

A mini truck is exactly what it sounds like – a small truck. It is a mix of a Pickup truck and a truck. They often have two or three seats and an open cargo area but can also come with a closed area. They are often built on a truck chassis and are often pretty strong built for heavy loading.

11. Truck

Most people know what a truck is. It is a two or three seated vehicle type, sometimes equipped with a bed behind the seats. It has a large cargo area and is primarily used for transporting goods by companies

DISPLACEMENT (LITERS AND CUBIC INCHES)

Engines are measured by displacement, usually expressed in liters (L) or cubic centimeters (cc). Displacement is the total volume of all the cylinders in an engine. An engine with four cylinders of 569cc each totals 2276cc, and will be rounder off and referred to as a 2.3 liter engine. Larger engines tend to produce more power — specifically more torque (see below) — but use more fuel.

Up until the early 1980s, engines were measured in cubic inches. One liter equals about 61 cubic inches, so a 350 cubic inch engine is about 5.7 liters.

TURBOCHARGERS

A turbocharger is a device that is used to boost the power of an engine. A four-cylinder engine with a turbocharger can produce as much power as a six-cylinder engine, but uses less fuel when driven gently. (For more information, see How Turbochargers and Superchargers Work.) Engines with a turbo sometimes get a T after their displacement; “2.0T” denotes a 2-liter engine with a turbocharger.

HORSEPOWER AND TORQUE

Horsepower and torque measure the amount of power an engine develops, with horsepower being the most commonly-used measurement. The difference between horsepower and torque is widely misunderstood (and difficult to explain).

Torque, which is measured in pound-feet (lb-ft or ft-lbs), measures pulling power; when you step on the gas pedal and the seat pushes into your back, you are feeling torque. Trucks need lots of torque to get their heavy loads moving. Horsepower is a function of torque and engine speed (RPM), and indicates how much sustained work the car can do. Racing cars need high horsepower to maintain high speeds. Generally, bigger-displacement engines develop more torque, but small engines can spin faster, which increases their horsepower output.

A car with high horsepower but low torque may feel sluggish from a stop, but will feel stronger as the engine spins faster and faster. A high-torque, low-hp engine will accelerate strongly from a stop, but will trail off as the engine speeds up (until the transmission shifts gears).

Horsepower and torque measurements are “peak” numbers; a 180 horsepower engine will only produce 180 horsepower at a certain engine speed — say, 6,000 RPM. At other speeds, the engine develops less horsepower. The same goes for torque, although some engines (especially those with turbochargers) have a sustained peak-torque range, developing their rated torque between, say, 1,800 and 4,000 RPM. An engine with strong mid-range torque (peaking between 2,000 and 4,000 RPM) will have good passing acceleration, while lot of low-end torque (below 1,500 RPM) is useful for towing trailers or driving off-road. However, cars with high-torque engines are more likely to slip and slide in rain and snow.

All that said, other factors, such as how much the car weighs, will affect acceleration. How the vehicle feels when you drive it is more important than the horsepower and torque ratings.