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BHP = Break horse power. It says that it is breaking horse power but it is generally relates with high pick up (your bikes reaches top speed in lesser time). So what does this actually mean?.

Torque = vertical distance x FsinΘ , how is that related to bikes and how does it affect performance?

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We just talked about this over here: mechanics.stackexchange.com/q/7922/57 –  Bob Cross Dec 20 '13 at 12:42

4 Answers 4

From Wikipedia:

Brake horsepower (bhp) is the measure of an engine's horsepower before the loss in power caused by the gearbox, alternator, differential, water pump, and other auxiliary components such as power steering pump, muffled exhaust system, etc. Brake refers to a device which was used to load an engine and hold it at a desired rotational speed. During testing, the output torque and rotational speed were measured to determine the brake horsepower. Horsepower was originally measured and calculated by use of the "indicator" (a James Watt invention of the late 18th century), and later by means of a De Prony brake connected to the engine's output shaft.

In the US, car's HP is rated at SAE net so as to give a truer value of HP available at the crankshaft. SAE net is the HP output of the engine after the alternator, waterpump, power steering, etc., are added to the vehicle. Automotive manufacturers used to use SAE gross, which is BHP equivalent. This gave a misrepresentation of what the owner could expect from the vehicle as far as performance. This all came about during the HP wars of the 60's and 70's.

EDIT: (realized I didn't answer the second part of your question)

Also, from Wikipedia:

Torque, moment or moment of force, is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist to an object. Mathematically, torque is defined as the cross product of the lever-arm distance and force, which tends to produce rotation.

In the automotive world (or bike world in your case), torque is the force which gets your bike moving. The more torque, the quicker the bike can move. You will usually hear two different terms: torque and horsepower. Torque is the twisting force; mechanical horsepower is a number derived from the equation

  • HP=(RPM * T) / 5252

Where -

  • HP = Horsepower
  • RPM = Rotations Per Minute (engine speed)
  • T = Torque

HP is usually considered the force which keeps the vehicle moving. HP the rate at which work is done.

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You wrote that torque is the twisting force "What it twists?". "It keeps it moving"; so torque is there when engine is off and bike downwards from a hill top? Then whats difference when bike moving when engine is off/on? –  paul Dec 17 '13 at 13:37
    
@paul ... The engine produces the TQ. When the engine is off, nothing. You have inertia (ie: mass in motions stays in motion). If going downhill, you have gravity. If you want to learn A LOT about torque, go to the Wiki page I posted. Since you posted about bikes, I will assume you have ridden one. When you apply the throttle, the front of the bike will come up. This is an application of torque. The engine revs, the torque is transmitted through the transmission, through the chain, to the rear wheel. The tire grips the road and the twisting force brings the front of the bike upwards. –  Paulster2 Dec 17 '13 at 13:44
    
When I give throttle in first gear bike's front tire jumps up(wheelie and stoppie)is this torque? But I can do that in my 125 CC Honda Stunner and 600 CC Honda CBR, so whats the difference? –  paul Dec 17 '13 at 13:53
    
@paul ... Larger engine, usually more HP/TQ. Part of the equation is transmission gearing. With a smaller engine, the lower gears of the transmission will have a numerically higher ratio to compensate for the lesser amount of HP/TQ. A transmission works on the principle of torque multiplication. If the first gear is 4:1, torque is multiplied by four times. If the engine has a TQ rating of 50 ft/lbs, the output would then be 200 ft/lbs. This enables a vehicle to start moving easier. As the vehicle continues moving, it takes less HP/TQ to keep it moving. –  Paulster2 Dec 17 '13 at 14:52
    
@paul ... The above examples are just numbers shown to help ease understanding. As for the two bikes mentioned, you'll have to look up what their HP/TQ ratings are as well as their transmission ratios to tell exactly what the differences are. Hopefully this helps a little in understanding how TQ works in a vehicle. And yes, when your front tire jumps up, this is torque at work. –  Paulster2 Dec 17 '13 at 14:54

BHP(Brake Horse Power) is the common rating that we consider while measuring the power of a bike. Technically it is the maximum power produced before it is delivered to the drive train. Torque is the turning effect produced by the engine. Peak Torque is available in lower RPM's. The naive categorization is :

In lower gears we get more torque. In higher gears torque decreases and power increases. When go uphill we require torque. HP is the other way. But an engine has different sweet points(RPM's). The one where it gains maximum power and the other where it gains maximum torque.

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Torque is how strong your engine is and Horsepower is a measure of how fast it can use that power.

That is why a Diesel engine with 400Nm of Torque cannot out-accellerate a petrol car with 400Nm of Torque. Horsepower is calculated by multiplying the amount of torque by the RPM of the engine (and dividing by 5,252. But that's not important here). Because a Diesel produces its power at say 2000 RPM, it's BHP figure would be rated at 152BHP, meaning that although it's a very strong engine, it cannot use that power very quickly. The petrol engine makes 400Nm at 6000RPM so the formula gives us 456BHP.

Both cars can pull a fair amount of weight, but only the petrol engined car can do so quickly.

I don't know anything about bikes or what is considered a "strong and quick" bike engine, but the facts remain the same.

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Torque is a turning moment. In an engine this moment is available at it's flywheel. Brake Horse power is the rate at which torque is applied.

An increase in engine speed implies a decrease in torque.

The faster your engine turns from rest, the greater the torque is applied, and so has greater HP. This applies only up to a point. As engine speed increases the torque will begin to drop off. Its HP output will become less efficient with further speed increases.

For most road going vehicles torque begins to drop off at around 2000 rpm, but HP at 3500 rpm. These fiqures can be manipulated by engine design according to what service the engine will be put to.

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