Feb 14, 2010

21 What is the difference between Power and Torque of a motorcycle?

An attempt to demystify the two terms that puzzles most of us.. which one should we use to compare bikes?

"Power' and "Torque" are two terms very often used to describe and compare the (engine) performance of motorcycles. Even if I have always had an idea of what these two terms meant, I have so far struggled to put it in simple words which any layman could understand.

Harley Davidson doesn’t even bother to mention the Power figures of its bikes in its tech specs..!!

A google search for these two terms will land you on numerous of web pages, each trying to explain in detail the definition and the difference between them. But as the definition often gets into the scientific equations and technical nitty gritties, I have always invariably ended up closing the web pages.

Recently I found a very simple explanation for the difference and explanation of Power and Torque on this site (www.HowStuffWorks.com)

"Power" and "Torque" demystified in 4 sentences in simple English (courtesy the above mentioned site)


    [1] Both Power and Torque are responsible for acceleration (which most of us also call as Pickup)

    [2] Power affects acceleration (pickup) at high speeds (higher engine speeds)

    [3] Whereas Torque aids acceleration (pickup) when the vehicle has to move from standstill or has to pull a heavy load (lower engine speeds)

    [4] Torque lets the engine to do the work (of moving the motorcycle), but Power lets it do the work quickly when you're already moving and pulling something heavy behind you





Which suits you better? A bike high on Power, or a bike rich in Torque?

To put things into perspective.. For Super Sports bikes like the Yamaha R1, Honda CBR1000RR, Ducati 1198, the talk always revolves around the Power figures.. rightly so as racy bikes need more engine grunt at higher engine revs.

Power

Power

On the other extreme, Harley Davidson, the maker of heavy cruiser bikes doesn’t even bother to mention the power figures of its bikes in its tech specs (Check out the Harley Davison site if you don’t believe me)..!!

Torque

Torque




To sum it up,

If you are inclined towards words like Sporty and Racy, "Power" should satisfy your need for speed.

If you don’t like to rev up the engine and want to take things at a leisurely pace, or if you have a heavy girlfriend/wife as pillion, you should probably talk more about "Torque".










Disclaimer:

This is to remind that the Views or Opinions in the blog are entirely mine unless explicitly stated. The Views and Opinions published in this blog should in no way be related to any other person or organization associated -- directly or indirectly -- with me.







21 Comments:

Sajal said...

As I understand it... and as you put it initially, the Power comes when you actually rev up the engine and the tach is reaching the read line...

It's like two bikes can reach 100kmph, but which bikes reaches 100kmph faster is a matter of Power... sheer raw Power.

Now, my bike can do a 100kmph @ say 7k rpm @ 5th gear, but can it do 25kmph at arround 2.5-3k rpm @ 5th clog and pull cleanly from there??? That's were the Torque of the bike kicks in...

Be it any bike, a bike is more and more fun, when the engine is designed to strike a more and more subtle balance between it's Torque and Power figures.... say for example the Ducati... killer Torque with all the required Power you need and the result is you have bike which can pop up the front wheel towards towards the sky even when you are on the 3rd clog.. :)

Payeng said...

@Sajal,

righly said. The above post is actually a very simplistic explanation for Power and Torque..

as you must be aware, there are many other aspects which determine the engine character like.. how the engine is tuned to deliver the peak power/torque (at what particular rpm), the number of valves per cylinder and also for multicylinder engines the cylinder layout ("V" vs "Inline")..

Ducati bikes sport the "V" configuration, which produces good torque compared to inline engines.

Sajal said...

yeah exactly!! It's the L-Twin of the Ducati Sports that does the magic... be it the 1098 series (848,1098 and 1198) or the Desmocedici.... amazing... they are all L-Twins with 2 or 3 valve configuration and look what they are capable of doing....

Not that zippy to begin with as compared to their inline cousines... but once these machines get going.... they go a long way!! No wonder Yamaha and Ducatis always make a close finish at the MotoGP scene :)

Anonymous said...

Your explanations (both of you) are effective in a simple manner. But i still do not understand the term BHP, which i suppose should stand for Breaking Horse Power. But i dont understand what it means.

Please shine some light through!!!

Nilkanth said...

I am a 1982 Graduate from V.J.T.I. in Mechanical Engg.
Please don't get confused with BHP , SHP & FHP
I will try to explain without getting into much detail.The basic relation between HP & Torque is given by the equation

HP = 2 x 3.14 x N x T
__________________ here N = RPM & T = Torque in kg-m
4500

The relation between peak power & peak torque depends on the Engine Tuning

Nilkanth said...

I am a 1982 Graduate from V.J.T.I. in Mechanical Engg.
Please don't get confused with BHP , SHP & FHP
I will try to explain without getting into much detail.The basic relation between HP & Torque is given by the equation

HP = 2 x 3.14 x N x T
__________________ here N = RPM & T = Torque in kg-m
4500

The relation between peak power & peak torque depends on the Engine Tuning

Anonymous said...

Yes, Horsepower is directly proportional to the engine speed(RPM) and Torque. Its how this equation plays the game when it comes to horsepower and torque. E.g., If torque peaks at a specific RPM and then decreases gradually, power can still continue to increase because increasing RPM will compensate for the falling torque; thereby pushing up the HP as a result of the product of RPM and Torque.

Later when the torque falls down substantially, RPM too having a peak cut out will no longer be able to push the horsepower to go up. Resulting in a fall of hp. Its all interrelated.

That said, though it may seem desirable to find a balance between power and torque for an engine. But it is largely practical because it is preceded by the purpose for which the engine will be used for; a litre bike meant for sport may be okay with lower torque at lower RPM but another might demand higher torque at lower RPM.

--biplab

Anonymous said...

There is a typo in my previous post. I meant "impractical".

Sorry, my bad.

--biplab

Anonymous said...

so what is better, honda cbr250r (power - 26.2BHP@8500RPM, torque- 22.9Nm@7000RPM) or kawasaki ninja250R (power- 32BHP@11,000RPM, torque - 22Nm@8200RPM)
nikhil

S.P - Biker Next Door said...

@Nikhil,

one can't just choose a "better" bike between the CBR250R and the Ninja 250R. Both bikes have different character in terms of engine performance.

I have ridden the Ninja 250R and its high revving engine has power/torque distributed till 13,000 RPM and therefore feels like a sporty race bike.

According to reports, the CBR250R has good low and mid range power/torque and is good for everyday + relaxed highway ride.

Abhinav Kumar Singjh said...

i just want 2 know that between honda cbr250r @ kawasaki ninja250R which is more faster in acceleration @ which is more faster in getting top speed

Anonymous said...

Points #2,3,4 are inaccurate. Acceleration at any speed is because of torque, or rather - available torque. Power itself is an illusory number, useful but not in the way depicted by you or how stuff works.

The thing is : talking about power and torque is no use by itself, because it has to be taken in context of something, without that context, it is meaningless.

Using heavy load vs high speed ( truck hauling tons vs F1 car ) is an apples to mango juice comparison.

Anonymous said...

@nikhil
1) CBR with torque 22.9Nm@7000 rpm will give u more pickup than NINJA 22Nm@8200RPM...becuae of more torque at lesser RPM. So CBR will overtake Ninja at the starts (speaking theoretically, but practically pickup matters bike+biker's weight and many other parameters like tyres ,gear ratios)

2) whereas after sometime i.e reaching some speed ninja will overtake CBR back becuz of its higher 32BHP@11,000RPM as compared to CBR's 26.2BHP@8500RPM which is less.

For a same bike power equals its torque around 5500rpm,
becuze of equation power = (torque x rpm )/5500

-vatsa

Anonymous said...

power = (torque x rpm )/5500
i.e. if u plot POWER,TORQUE curves against RPM.
around 5500 rpm POWER,TORQUE curves intersect, and after 5500 rpm magnitude of POWER is more than TORQUE, hence at higher RPMs POWER becomes more significant but is derived from TORQUE...
-vatsa

Nagendra said...

Very informative. It helps me to buy perfect bike. Thanks you.

Anonymous said...

@Anonymous
Thanks for the information. I do not think anyone can give a better explanation than you have.

Anonymous said...

Please check on the internet.. There is a web site that has an article comparing performance of Ninja 250R, CBR 250R and Hyosung GT250 bikes. They have shown graphical illustration of change in the torque and horsepower at particular RPM. And S.P. has already said that one can't just choose a 'better' bike between the CBR250R and the Ninja 250R (and the GT250).
-Shree

abhilash nair said...

its not always 5500rpm.it varies according to make.look at the specs and you will see power/x rpm(eg 25bhp/8500rpm).that is the rpm where you get the most power from the bike.trying to keep the rpm close to that number will give you maximum acceleratiom figures.but till you reach that rpm the torque is important.the gear ratio,torque,power,weight should be taken into account when deciding a better bike.it cannot be decided just by looking at the torque&power values.also how a bike holds up when cornering ,braking etc is also very crucial.

KB said...

That's a really poor explanation of what torque and power are.

Advait said...

Torque is the pulling power, which gives bike the power to reach a speed. That may be from 0 to 20 kmh (potential energy to kinetic energy), and above. This is said on 'Fifth gear' an auto show on discovery turbo.

Power (bhp) is just to maintain speed. Thats why at 3rd and 4 th gear we feel less vibration. And no need to accelerate more at high rpm. Thats why we get mileage at higher gears.

Brake horsepower (bhp) is the power given to wheels by the engine.

Most of people have myth about the term 'cc'. Its not the power, but consumption of fuel to give power. It stands for cubic centimetre. Its a unit of volume. Hence, a 100 cc bike will take 100 cc (0.1 litre) of fuel to complete one cycle of the engine. Hence, a 100 cc bike will give more mileage but less power than 125 cc and 150 cc bikes. Now u can guess the mileage once u know the term 'cc'.

More fuel, more power. Less fuel, more mileage. Many auto makers are trying to balance the power and mileage by introducing new technology in engines.

Anonymous said...

Get the new ninja 300 cheapsters.itz awsum

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