Motorcycle specs – Demystified

“Four strokes”, “Single Cylinder”, “Cubic capacity”, “BHP” are some of the terms we bikers use in our daily lingo. Some of the moto-geeks as explained in one of our previous articles will laugh at the silliness of my writing up this one. For them, talking about these terms comes as naturally as breathing. However, majority of us surprisingly have no to little knowledge about these terms. To be honest, I had average knowledge of all these terms till about 11 pm last night after which I read through whatever I could find on the internet for the next 4 hours and now I feel like a Zen master ready to preach all his learning.


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Note – This article is aimed at laymen and beginners and I have attempted to explain the terms in the most easy to understand way. The whole idea is that by the end of this article a statement like “The KTM RC 390 is a single cylinder, 373 cc bike which produces maximum power of 43 bhp @ 9000 rpm and maximum torque of 35Nm @ 7000 rpm, having a liquid cooled engine, with four valves and fuel injection, which is powered by a 6-speed manual gear box having inverted telescopic fork front suspension and a swing arm mono rear suspension with disc brakes on both wheels ” does not sound gibberish to the average person.

Let’s start by understanding how a motorcycle works in the most basic of ways. As we all know that there is an engine which runs on some kind of a fuel (mostly petrol), the fuel creates a kind of a combustion in the engine which results in the rotation of something called a crankshaft with the help of pistons (more on crankshafts and pistons later), the power created by the rotation of the crankshaft is transferred to the real wheel of a motorcycle usually by a chain or a belt. This propels the motorcycle forward. The direction of the motorcycles is controlled by the movement of the front wheel and brakes made out of rubber or discs helps you in slowing or stopping the motion of the motorcycle. To make this whole process more efficient, we have gears and a clutch.


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It is time to get down to demystifying the specs, starting with the engine.

Types of engines – There are primarily three ways to classify engines, by the capacity of their combustion chamber (cc), the number of cylinders it consists of and the number of strokes in their power cycle. Most of the motorcycles today run on four stroke engines. We also have some bikes running on two stroke engines. One should not confuse a two stroke bike with a two cylinder bike. They both are entirely different concepts which I will explain shortly. The four strokes in a four-stroke engine are defined as follows:

Stroke 1 – Intake valve(s) open, piston moves down, sucking in the air/fuel mixture.
Stroke 2 – All valves closed, piston moves up, squeezing the mixture.
Stroke 3 – All valves still closed, spark plug ignites the fuel/air mixture, pushing the piston down.
Stroke 4 – Exhaust valve(s) open, piston moves up, blowing the old charge out the exhaust valves.
A short version is Suck, Squeeze, BANG, and Blow.


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Displacement – The most common term to identify motorcycles is by its cubic capacity or cc or its displacement. Basically, a motorcycle engine consists of pistons which move up and down driven by explosions of fuel-air mixture which is ignited by a spark. This movement of the pistons make the crankshaft to move in a rotary action which then powers the rear wheel as mentioned earlier.  Cubic capacity basically refers to the volume displaced in the cylinder of an engine as the pistons move from their bottom position to their highest position in the cylinders. In other words, cubic capacity is the volume swept by the piston in a cylinder from top to bottom. The higher the volume, the more movement for the piston which will further make the crankshaft rotate more which will directly affect the movement of the rear wheel.

Cylinders – The cylinder is basically the chamber where the piston moves up and down. Most bikes in India have single cylinders. However there are bikes which have up to six cylinders too. Bikes can also be classified by the way the cylinders are placed in an engine. For example, a V-Twin engine has two cylinders placed in a “V” shape usually at an angle of 45 degree.


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Valves – valves are basically components in an engine which control the passage of the fluid or air in the engine in a single direction by closing or opening. Different makes of motorcycles have different number of valves based upon their engines. A bike with more valves will not mean a bike with more power or vice-versa. It will only mean more inlets and outlets for the movement of the fluid or air in the engine.

Cooling – Since so much of action takes place inside an engine, it tends to heat up real fast. There are several ways to cool down a heated engine. An engine can be liquid-cooled by running coolant through the engine and exchanging the heat via a radiator. It can also be air-cooled by airflow over fins on the engine. Another variation is oil-cooling where engine oil is circulated in the engine and its heat exchanged by a small radiator.

Fuel system – There are basically two ways to control the mixture of fuel and air which is sucked inside the first intake valve of an engine. One is the good old carburetted system and the other is new automatic method of fuel injection. The only advantage I can think of a carburetted setup is that it is fairly simple to repair and most mechanics in our country are equipped to do that whereas in case of a problem in a fuel injection system it will have to be replaced more often than not. The fuel injection system is far more advanced and provides much better cold starting, better throttle response, better fuel efficiency and less maintenance.

Torque – Torque is basically a force that tends to cause rotation. Peak torque in a motorcycle will essentially mean the twisting force given by the engine and at what value of engine revolutions per minute (RPM). It can be simply explained as the twisting force. Torque is that quality of the engine that is expressed when you use the throttle aggressively and accelerate hard. It is just the feeling and needless to say will be felt as more forceful when the number is high.

Power – Horsepower is the measurement of power. BHP or brake horse power in motorcycles basically implies the highest amount of horsepower produced by an engine before there is loss in power due to various factors like gearbox, drive train, etc. So the statement “produces maximum power of 43 bhp at 9000 rpm” would mean that the RC 390’s engine would produce maximum power of 43 bhp when the engine is moving at 9000 revolutions per minute.

Note – High power and high torque will not essentially mean a very fast or very good performing bike. The idea is to get a balance between the two. A very simple explanation will be that good torque will help you with faster “of the mark acceleration” but then you will need a healthy bhp curve to carry on the momentum to its top speed.

Transmission – Transmission is the whole process of transferring the power produced in an engine to its real wheel in a controlled manner. The whole process mainly comprises of gear set, clutch and drive system. The set of gears enables the rider to move from a complete stop to the desired speed in a controlled manner. Usually bikes have 4 to 6 gears and the change of gears is manually done by the rider. The job of a clutch is to engage and disengage power from the engine crankshaft to the transmission which ensures smooth gear changing. The drive system forms the link to transfer power from the crankshaft to the rear wheel. The most commonly used drive system is a chain mounted on a sprocket, followed by a belt which is more popular in scooters and the least used system is a drive shaft.

Chassis – The motorcycle chassis consists of the frame, suspension system, wheels and brakes. The frame forms the skeleton of the bike which is made up of hollow tubes of steel, aluminium or alloy. The suspension system is a collection of springs and shock absorbers that helps to keep the wheels in contact with the road and cushions the rider from bumps and jolts. There are various kinds of suspension systems like swing arm, telescopic fork, inverted fork, mono shock, etc. Traditionally, motorcycle wheels were generally made up of aluminium or steel rims with spokes. The alloy wheels are today the most common wheels used in India. The tubeless tyres are fast catching up with conventional tube tyres. One of the oldest forms of brakes are the drum brakes which are being fast replaced by disc brakes. The ABS or Anti-lock Braking system is a computerized method of braking which does not lock the wheels of the bike while braking, making panic braking safer than ever.

1009 Chassis Design Side 040210

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So after all this gyan the bottom-line is that the statement “The KTM RC 390 is a single cylinder, 373 cc bike which produces maximum power of 43 bhp @ 9000 rpm and maximum torque of 35Nm @ 7000 rpm, having a liquid cooled engine, with four valves and fuel injection, which is transmitted by a 6-speed manual gear box having a inverted telescopic fork front suspension and a swing arm mono rear suspension with disc brakes on both wheels” still sounds gibberish to you? Oh well, I wasted a peaceful night’s sleep if it does.

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  • Battu Raju

    Fantastic Specifications
    Superb SpecificationS

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