What is bore? What do they mean by V-twin? If you are unaware of the very basic bike terminology, this article will help you understand the fundamentals the next time you read any motorcycle’s spec sheet…

You often come across terms which are almost used everytime someone describes a motorcycle, which you do not understand. Terms in a motorcycle’s specification that is listed on company’s pages, websites, may seem a little complex for a person who is not well versed with motorcycles, or engines, in general! In this article I am posting about the very basic understanding of bike stuff. Time to learn!

Definition of some of these terms can be as exhaustive as a thick book but as the heading infers, here I am trying to only give you the very basic understanding. These definitions of the terms used in the motorcycle specifications are intended to help you to learn more about bikes in general. The more you understand about your bike there is a likelihood that you will treat it better.

Bike Jargon Explained

No. of Strokes: Do note that we are discussing only four-stroke motorcycle engines and not two-stroke motors. I also urge you not to get confused between four-strokes and four-cylinders or two-strokes with two-cylinders because they are completely different from each other.

The definition of the four strokes in a four-stroke engine is as follows:

  • Stroke 1– Intake valve(s) open, piston moves down and the air/fuel mixture is sucked inside
  • Stroke 2– All of the valves are closed, piston moves up squeezing the mixture.
  • Stroke 3– All of the valves are closed and a spark plug ignites the fuel/air mixture, pushing the piston down.
  • Stroke 4– All but the exhaust valve(s) are open, piston moves up, blowing the old charge out of the exhaust valves.

A short version is Suck, Squeeze, Bang and Blow.

Cooling: By running a coolant through the engine the heat generated can be exchanged through the radiator just like in a car (for liquid-cooling). Air For air-cooling, regular air flows on the fins of the engine to cool it down. Another method of engine cooling is oil-cooling wherein the circulation of engine oil takes place in a small jacket ahead of the engine. In this process the engine oil is cooled by air and this cooled engine oil is what gets circulated inside the engine.

Air Cooled vs Oil Cooled vs Liquid Cooled Engines – Explained in Simple Terms

Valves: The use of the valves is as mentioned above. For the purpose of intake and exhaust; however, there maybe use of one or more valves. The number of valves used per cylinder or for the whole engine maybe indicated by bike manufacturers. As the indication of closed and opened valves, terms such as SOHC (Single OverHead Cam) or a DOHC (Double OverHead Cam) etc., are also used. To operate the valves, there are other methods as well.

Bike Jargon

Number of Cylinders: There will be as many as 1 to 6 cylinders in the engines. Small bikes which we get in India traditionally use a single-cylinder engine. Engines with two-cylinders arranged in several configurations can be seen in many bikes that include:

  • V-twin – Here the cylinders are spaced at a particular angle looking like a V to the onlooker.
  • Parallel twin – In this, the two cylinders are right next to each other in a vertical position.
  • Flat-twins – Here the two cylinders are opposed as seen in the BMW Boxers.

There are many engines that come with more than two cylinders. They include:

  • Triples – three cylinders are lined up next to each other in a vertical position, say the parallel triples.
  • In-line fours – this is similar to a triple except with another cylinder added to it.
  • V-4 engines – four cylinders and placed as V, like the one used in Ducati Panigale V4.
  • V-6 engines – six cylinders as V, like the ones used in Boss Hoss.
  • Flat-6 engines – six cylinders like the one used in Honda Gold Wing 1500/1800s.

There are other engines as well but right now let us keep it limited to these only.

Displacement:
The volume displaced as the pistons move from their bottom position to their highest position inside the cylinders of an engine is called as displacement. Measurement of displacement is either in cubic centimeters (CC) or cubic inches (CI), although, in India cc is the more frequently used term.

Bore and Stroke: Diameter of the cylinder in the engine in which a piston moves up and down is bore and the distance which the piston moves up and down in the cylinders is known as stroke.

Fuel System:
To control the mixture of air and fuel, carburettors or fuel injectors are used. During Stroke 1, the mixture of air and fuel get prepared to be sucked through the intake valves and in through the cylinders. The carburettor name and the number of carburettors used are usually identified by the specifications. Fuel injection (FI), Digital Fuel Injection (DFI), Programmed Fuel Injection (PGM-FI), Electronic Sequential Port Fuel Injection (ESPFI) etc are the different names used by different bike manufacturers for the same tech of fuel injection.

Compression Ratio: Compression Ratio could be explained like this: Take some 100 cc water and pour it through the sparkplug hole when the valves are closed and also when the piston lies at the cylinder bottom. Then, it is like full. And, you can at the most pour only 10cc of water in to the hole to fill it, when the piston comes at the top of its stroke, then the ratio for compression is 100 to 10 or simply 10 to 1. Engines make more power when there is a higher compression ratio also implying that they require more fuel.

Maximum Torque: Torque is the maximum amount of twisting force given by the engine and at certain value of engine revolutions per minute (RPM). It can be simply explained as the pulling power of an engine. The lower the engine rpm, the easier it is for a motorcycle to push load. As a very basic example, Royal Enfield’s, owing to their higher torque are good at ‘pulling’.

Maximum Horsepower: It is simply the power produced by an engine and occurs at a particular engine speed. It can be derived through the formula : Horsepower = Torque × RPM/5252. This also tells us that both the horsepower as well as torque are interrelated.

As we said, this is just the very basic definition of these terms. You can head to our ‘Informative’ section to read more such stories…

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22 COMMENTS

  1. nice one here deepak…

    @balu…
    torque is the rotating power…the ablity to turn… the initial pull the the engine generates… the straight motion of the cylinder of the piston is converted to rotating motion using a shaft or a lever… Torque is the force that tends to rotate or turn the shaft..

    horse power is something that keeps the torque goin… sustain the torque generated…

  2. Can u please tell me how Shhort Handles Effect the Bike
    Does bike with short handle is safer to drive at high speed or not

    Also tell that what is Tachometer

  3. The pictures seem to be apt for this piece of article! I liked it. Waiting for more information on short-handled bars! Would you mind explaining how a fuel mixture is ignited inside a cylinder and how can a mileage of say 35-40 kmpl is achieved and what will be the difference in the engine if the fuel is different. Any thoughts appreciated!

  4. Hi
    could you explain some smoe more on how rpm/torque/horsepower works and how they are inter rellated to each other
    some specifications are in the terms of NM/PS/BHP/ etc
    why different notations ?
    what are the significances ?

    Thanks in advance
    Sudhir Sangwan

  5. some specifications are in the terms of NM/PS/BHP/ et

    Dear all

    BHP = Breaking Horse Power

    the formula for the BHP is bhp = torque * rpm/5252

    PS = Power to Shaft

    It is german word which use to judge the power of Engine. It is mostly used in Eurpoe & south America. The only difference is BHP takes 746 watts while PS takes 736 Watts.

    NM = Newton meter

    The definition for the same is

    One newton metre is equal to the torque resulting from a force of one newton applied perpendicularly to a moment arm which is one metre long.

  6. Dear Seeram,

    Fuel quality is judged by Octane. Higher octane means lesser carbon ppm (Parts per million. As we know carbon is the biggest enemy of engine. Lesser amount of carbon ensure healthy engine life and result into better fuel efficiency.

    Moreover engine compression ratio is directly related the octane of fuel. The higher the compression ratio the higher octane to be used.

    One hidden fact is that most of new engines require better quality octane But in India we have only 87 and 91 octane max to max 93.5 octane petrol but which is available to very few people.

    Thanks

  7. EXAMPLE

    2009 Yamaha MT-01 – Candian Specifications
    MSRP: C$16,099

    Engine Air-cooled, OHV, 8-valve, 48 degree, V-twin
    Displacement 1670 cc
    Bore and Stroke 97 x 113 mm
    Compression Ratio 8.4:1
    Maximum Torque 15.3 kg-m (110.7 ft-lb) @ 3,750 rpm
    Fuel Delivery 40 mm Mikuni throttle body F.I.
    Lubrication Dry sump
    Ignition Digital TCI
    Transmission 5-speed
    Final Drive O-ring chain

    Suspension (Front) Fully adjustable 43 mm inverted fork
    Suspension (Rear) Fully adjustable link Monocross
    Brakes (Front) Dual 320 mm discs
    Brakes (Rear) 267 mm disc
    Tires (Front) 120/70ZR17
    Tires (Rear) 190/50ZR17

    Length 2,185 mm (86″)
    Width 800 mm (31.5″)
    Height 1,105 mm (43.5″)
    Wheelbase 1,525 mm (60″)
    Rake / Trail 25° / 103 mm (4.1″)
    Ground Clearance 145 mm (5.7″)
    Seat Height 825 mm (32.5″)
    Fuel Capacity 15 litres (3.3 imp. gallons)
    Wet Weight 260 kg (572 lb.)
    Colour(s) Metallic Black

  8. how do i adjust the valve settings of my discover 125 dts-i i think n feel tht the correct valve settings r 1 of the most importnt factr affecting bikes performance

  9. sir,
    whats the uses of tachometer in a bike. i mean its practical use while driving the bike,when idling, while servicing.

    whats its main purpose? ofcourse it indicates rpm of engine shaft rotations per minute. but how far its useful to a practical rider ih his day to day driving.

  10. How can I install security system in Honda CB Twister? Will it create any problem in the bike as Twister has a small battery?

  11. hi deepak ,
    engine rev per minute must be less or more ? and can u clearly tell me wat that twisting power is (torque) … im a commerce student actually so i cant understand technical english which r used in phyrics n mechanics 🙂

  12. hi deepak….nice one….would appreciate a more eloborate one which could explain in more of layman’s language….explaining the jargon’s in practical riding situations for the newcomers of bikers’ community to read,understand,apply and enjoy riding….for example an explanatyion could be put explaining the methodology and relation between rpm, road speed and gears….what should be the average acceptable gear related to road speed and the corresponding rpm or vice versa….to be more precise: in tvs apache rtr 160 hyper edge rear disc bike: what could be the corresponding/guiding display in the dashboard: driving road speed in km/ph; rpm needle position; and what gear to be engaged….i don’t insist the brand as this is only for explaining purpose as i choose this one because i own one….as you have promised a V.2 of bike jargon in layman’s language would be very helpful for us folks….hope you will be blessed with some quality time and opportunity to do this peace of research……..

  13. hi all. I own a Bajaj Discover DTSsi 125Cc 2005 model. my bike after performing well for 4 year has been creating problems since last 6 months in average area. My bike is not giving mileage more than 25-27 kmpl. I have got the bore and piston changed a new one on recommendation of one of the authorised Bajaj service station but of hardly any use. AFter giving mileage of 40, twice its back to 25-27. I am fed up with this bike. I have changed to better quality of fuel also but still no improvement. Friends any one of u can help please.

  14. HI all

    Can you please tell me the meaning of 13 bhp @ 8500 rpm or 11.1ps @ 7500 _(figures are just for example .)

    more bhp mean more power but what about RPM … ,,,

  15. Dear mayank,.
    13bhp at 8500 rpm.
    First of all BHP means Breaking Horse Power i.e the output power available to the crankshaft.
    RPM MEANS ROUNDS PER MINUTE OR U CAN SAY CYCLES PER MINUTE . fOR A 4 STROKE BIKE THERE ARE 4 STROKES NAMELY –
    1. Intake
    2. Compression
    3.Power stroke
    4.Exhaust stoke
    These 4 strokes ina sequence makes a cycle or a round in a engine . thus 8500 rpm means the engine is making 8500 rounds/cycles per minute to produce 13bhp of power to the shaft

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