Difference between power and torque

[Minacious]

I say something somewhat close to what Ronin put. The simplest way I look at it - Torque gets you going, Horsepower keeps you moving.

[T-Bird]

exactly Torque moves the car from a stop the best way to back that up is that a Trannsmission is only dealing with Torque in the sense of making the car move same with the gearing in the rear end. Changing your rear end gears and your transmission gearing and Torque converter (if an Automatic) will get you alot more Torque but won't get you anymore HP because HP doesn't make the car move it just keeps it moving once you get it going.

[caneswell]

Torque is what accelerates a car. BUT this is torque at the wheels not flywheel torque. So if an engine has high torque at low rpm the gearing required to make the wheels rotate at a usefull speed, reduces the torque at the wheels dramatically. This is why diesels are slow.

Power is a much better perfomance indicator because it takes engine speed into account. Power = torque x rpm. So power and weight are all you need to give a pretty good indication of a cars performance.

[Pokiou]

torque shows how quickly you get to your peak Horse power...

[Yablokov]

omg, ty so much guys, i was gonna post this same thread few days ago. good thing i got this answered. it took me about 8-9 posts to start understanding the concept lol!

[Blip]

sorry to bump this up but i found another explanation. I copied the entire article here so that it can remain as a reference on JW, in case the original site is gone.

Article from www.flamesonmytank.co.za/Articles/torque.htm

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Torque v Horsepower


While these two topics can get very scientific here is a overview that you will find useful.

Torque

Torque is the ability of the engine to continue to twist (rotate) the rear wheel with great force. Torque has nothing to do with speed. Maximum torque is not to be found at the highest revs but somewhere below that - perhaps as much as 25%. Because lower revs are involved, the rear wheel is less inclined to spin and loose traction - an important issue when riding your bike up a steep gravel road.

Horsepower

Horsepower is the ability of your engine to move your bike forward at a certain speed - the higher the speed, the shorter the time taken, the greater the horsepower needed.
Every engine has its own characteristics of torque and horsepower - something you as the rider can only learn with experience and hopefully, not too much trial and error! In the example below the engine develops the most torque at 4000 rpm before it starts to drop again. By contrast the horsepower available increases steadily all the way to 5000 rpm.



Practically what does this mean for me the rider? Let us take the BMW F650 as an example. The bike's manual gives the following technical specs

. Maximum permissible rpm 7500
. Maximum rated capacity (horsepower) 35 kW at 6500 rpm
. Maximum torque 57 N.M. at 5200 rpm

From this we can see that the difference between max torque and max power is 1300rpm - quite a big gap that we must utilise for different conditions.
Consider these two scenarios below based on the specs in the table above. (Your bike will have its own characteristics - consult your manual)


Scenario One

You are traveling along on your motorcycle on a country road behind a long truck doing about 85km. The oncoming traffic is heavy. Things are going to be tight. You will need maximum torque for fast acceleration and maximum horsepower for the necessary speed to take you past and beyond.

The gap you are waiting for arrives! You check your rev counter and it is sitting around 3000rpm. The specs tell us that 5200rpm delivers the maximum torque. The situation demands the maximum. You change down a gear and the revs shoot up drawing on the torque available. You open the throttle up and gun the bike into the gap.

The bikes speed and revs climb quickly. There is not much point taking the revs past 6500 as the horsepower begins to level off after that (the maximum rated capacity). You change to a higher gear and the revs drop back towards the 5200 mark allowing you to again draw on the torque to give added impetus to the bike's acceleration.

Again the bike's speed and revs climb quickly. As you do not have another gear to change to you keep the throttle wide open gunning for 7000 rpm. Here the bike is using its horsepower to cover greater and greater distance in a shorter and shorter time period (distance over time i.e. speed)

By now the truck is a speck in your mirror and it's time to relax and check to see that your passenger was not left somewhere behind on the tarmac!


Scenario Two

You are travelling up a steep gravel-road mountain pass on a 4 x 4 route. You do not want the motorbike to falter and equally you do not want to go too fast. Thus you change to whatever gear that maintains the revs around 4500rpm and maintains the desired speed. This still gives you some extra torque to use if you need it (from 4500 to 5200 rpm)

If both the speed and revs begin to increase you can change to a higher gear and bring them back down. If the speed and revs begin to drop below 4000rpm it is time to change to a lower gear and bring them back up. At all times the idea is to keep the bike in striking distance of the maximum torque level (sometimes called the powerband - yes, confusing as it has nothing to do with horsepower)

The great thing about this topic is that we naturally know all of this just by doing. Listening to the engine and feeling the amount of power still left untapped is the real teacher in this instance."

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[irrational_i]

There are some good explanations.
Another one I know for the engineers:

Torque is water pressure, Power is water flow.

another:

Torque is how hard you punch a bag, Power is how fast you punch it.

[AlexBlaster]

[quote="Evo"]

Originally Posted by ZfrkS62 a quote i've seen before on some forum "Power sells cars, torque wins races". not sure how true that is, though. Think Henry Ford said that.. I might be wrong though. or was it Shelby

It was Carroll Shelby who said it best: "Horsepower sells cars, torque wins races."

[bullet_1800]

The way i have experienced it so far.... Torque is what makes you think your car is fast. Power is what actually makes it go fast.