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Old 05-22-2006, 1:16 AM   #1
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What’s the difference between torque and power?

This has been posted as an article at CongSoft's invitation.

What’s the difference between torque and power?

Torque is a measure of the twisting force an engine can generate. Essentially torque is what you feel when you open the throttle on your bike and accelerate. Torque is not a fixed figure and in fact, the published torque of an engine (as measured at the crankshaft) is really quite meaningless unless you take gearing into consideration. For example, many bikes have enough torque to power wheelie in 1st gear but few can power wheelie in 6th gear. Put simply, we can either have a lot of torque at the rear wheel or a lot of rpm — but not both. Every time we change up a gear, we are trading torque for rpm.

This is where power comes in. Power is a combination of torque and rpm. An engine can produce little torque at the crankshaft but if it revs high enough can still produce a lot of power. Conversly, an engine might not rev very high but if it has a lot of torque it can produce a lot of power.

This may be easier to understand if we compare a 1200cc Harley-engined Buell XB12 and a 600cc Yamaha R6. The 1203cc XB12 engine produces 111Nm crankshaft torque at 6,000rpm and the 599cc R6 engine, 66Nm crankshaft torque at 12,000rpm.

Despite the fact that XB12 produces double the torque of the R6, due to gearing differences, maximum acceleration in top gear at the bikes’ respective torque peaks is roughly the same. The big difference however is that the Buell only revs to 7000rpm whereas the R6 redlines at 17,500rpm (although apparently this figure is a little optimistic!).

High rpm equates to high horsepower, consequently, the Buell only makes 74.6kW, while the R6 makes an amazing (for a 600) 93.4kW. Hence while the Buell runs out of puff at 230kmh in top gear the R6 will pull to around 265kmh.

One thing that is worth bearing in mind is that with the R6, as with many other bikes that claim high max hp ratings, unless you are riding above 11,000 rpm, you will never get to experience most of that power. This is because even in 1st gear 11,000rpm on bikes like the R6 equates to about 100kph. So if you regularly experience life above 11,000 on city streets, it is only a matter of time before you get arrested!

Truth be known, a low revving, high torque bike has much more accessible power for the street and is therefore a lot more practical in the real world than a highly strung, high revving 600cc race-replica. But then again, who ever said motorcycles had to be practical?!

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Old 05-22-2006, 7:16 AM   #2
 
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Re: What’s the difference between torque and power?

HP is measured by how fast you hit the wall

Torque is measured by how far you move the wall when you hit it.
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Old 05-22-2006, 7:25 AM   #3
 
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Re: What’s the difference between torque and power?

Nice read...also it should be noted that if your torque curve is decreasing at a slower rate than your RPMS are rising you will increase your horsepower.
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Old 05-22-2006, 10:04 AM   #4
 
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Re: What’s the difference between torque and power?

http://vmaxoutlaw.com/tech/torque_hp.htm

See what you all think of this...
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Old 05-22-2006, 10:11 AM   #5
 
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Re: What’s the difference between torque and power?

Your article looks like an argument for your bike more than an explanation of torque.
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Old 05-22-2006, 11:02 AM   #6
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Re: What’s the difference between torque and power?

Originally Posted by luvtolean
Your article looks like an argument for your bike more than an explanation of torque.
The fact is I do prefer the low rpm torque of the Buell XB12 over a high revving 600 inline 4. Sorry if some bias crept into the article as a result.

I don't believe however that using the specs of a bike I own changes the usefulness or validity of that example. The fact is that coincidentally, the Yamaha R6 and Buell XB12 have similar drive at the rear wheel in top gear - one at 12,000rpm and the other at 6000rpm. It boils down to what you like and how you ride.

(Of course I could have used the example of my Powercommander and Akrapovic-full-system equipped 954 Fireblade vs. the Buell - in which case the 954 would have proved the "superior" bike. Despite this, I enjoy riding both bikes equally.)

Last edited by ndj; 05-22-2006 at 9:05 PM.
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Old 05-22-2006, 11:16 AM   #7
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Re: What’s the difference between torque and power?

For a better, less bias understanding look here. Also check out the related articals at the bottom.
http://auto.howstuffworks.com/question622.htm
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Old 05-22-2006, 11:19 AM   #8
 
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Re: What’s the difference between torque and power?

Quick question...if your motor makes 78 HP at 5,252 rpm...what is it's torque....
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Old 05-22-2006, 11:22 AM   #9
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Re: What’s the difference between torque and power?

Originally Posted by Baketech
Quick question...if your motor makes 78 HP at 5,252 rpm...what is it's torque....
I don't actually read the links I submit.
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Old 05-22-2006, 11:55 AM   #10
 
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Re: What’s the difference between torque and power?

Originally Posted by Baketech
Quick question...if your motor makes 78 HP at 5,252 rpm...what is it's torque....
If it's -40ºF...what is it in ºC?
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Old 05-22-2006, 12:02 PM   #11
 
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Re: What’s the difference between torque and power?

That pitch was high and inside...
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Old 05-22-2006, 12:07 PM   #12
 
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Re: What’s the difference between torque and power?

Originally Posted by Baketech
That pitch was high and inside...
Just like I like 'em.
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Old 05-22-2006, 12:16 PM   #13
 
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Re: What’s the difference between torque and power?

Originally Posted by Baketech
Quick question...if your motor makes 78 HP at 5,252 rpm...what is it's torque....
Another question: What is the possessive form of "it"? "its" or "it's"?
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Old 05-22-2006, 12:18 PM   #14
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Re: What’s the difference between torque and power?

Originally Posted by tigerblade
Another question: What is the possessive form of "it"? "its" or "it's"?
MINE!
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Old 05-22-2006, 12:19 PM   #15
 
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Re: What’s the difference between torque and power?

Originally Posted by tigerblade
Another question: What is the possessive form of "it"? "its" or "it's"?
I personally just like using the apostrophe...it's cool. Just say it out loud...even that's cool.
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