Torque vs HP | GTAMotorcycle.com

Torque vs HP

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Basketcase

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It seems that all of the 600 - 650 cc bikes have very similar torque figures - 45 ft-lbs +/-. However the horsepower numbers vary quit a bit.
If i have two bikes with the same weight and gearing and the same torque would they have similar roll-on power. From 100 - 120 kph would they give the same kick in the pants? Would the main difference be in the top end speed? What about 0 - 60 mph times?
 
The simplest way of comparing performance of one motor to another - look at a graph of HP over RPM, preferably where the different motors/bikes are overlaid on the same chart. If you're worried about having the fastest 600 in a straight line, don't - there are only very minor differences between bikes of the same generation.
 
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Basketcase said:
It seems that all of the 600 - 650 cc bikes have very similar torque figures - 45 ft-lbs +/-. However the horsepower numbers vary quit a bit.
If i have two bikes with the same weight and gearing and the same torque would they have similar roll-on power. From 100 - 120 kph would they give the same kick in the pants? Would the main difference be in the top end speed? What about 0 - 60 mph times?
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Torque is a measure of force, how hard the engine can turn. Horsepower is a measure of work, force applied over a period of time. Generally, the absolute torque value of an engine of a given displacement is similar among engine layouts. The presentation or characteristics of the power curve can be affected by the engine layout however. Low-revving twins, which have a reputation of "lots of torque", don't really have more torque. It's just more accessible at a lower rpm. Bikes with a lower rev ceiling are generally geared higher to take advantage of the torque at lower rpms. Conversely, bikes with more revs generate more horsepower. They have to be geared lower to get up to the power peak for that type of engine.

In general, a bike of equal displacement that makes more horsepower and is geared for the type of race in question will be faster than a bike that makes less horsepower, regardless of whether the torque number is equal.
 
Someone told me horsepower was how hard you hit the wall and torque was how far the wall moved. :)
 
It is simple... HP = (Torque*RPM)/5252 (formula is for imperial units...).

The HP numbers just relate to how much torque is being made at what RPM. Another interesting point, all motors make exactly the same "number" HP and Torque @ 5252 RPM. Below 5252 the motor will always have a higher torque number, above 5252 the motor will always have a higher HP number.

In drag racing (although not entirely true) the generalization was your ET had a strong relationship to torque, the trap speed to HP.
 
Basketcase said:
It seems that all of the 600 - 650 cc bikes have very similar torque figures - 45 ft-lbs +/-. However the horsepower numbers vary quit a bit.
If i have two bikes with the same weight and gearing and the same torque would they have similar roll-on power. From 100 - 120 kph would they give the same kick in the pants? Would the main difference be in the top end speed? What about 0 - 60 mph times?
Click to expand...
That is the biggest problem nowdays. Manufacturers just post the max figures, such as max torque. The problem with this approach is that it tells you very little about the engine. They key is the torque curve.

Once you see the torque in relation to the RPM for the entire RPM range then you can truly compare performance of engines. The HP rating of the engine is the highest potential it has for producing power. So say you look at your torque curve and it peaks at 12,500 RPM. You will then take that RPM and that torque, plug it into a formula and you will get yourself HP value.

Now you may wonder why the max torque and max HP are not always at the same RPM. Well that has to do with how quickly the torque decreases after you hit the maximum. Say you hit the max of 48ftlb @12,500 RPM. But you still get 44ftlbs @15,200 RPM.

For the first set of numbers you get (48X12500)/5252 = 114
For the second set you get (44X15200)/5252 = 127

So your torque is no longer at it's max, but it is still high enough at that RPM to produce a higher horsepower rating.

The way engines work is higher displacement produces higher torque because you get more fuel+air into the cylinder, which means bigger explosion, which means more power. But the tradeoff with higher displacement is that they are unable to achieve RPMs as high as engines with smaller displacements. At the end manufacturers try to balance these characteristics with gearing to achieve the smoothest power delivery (or at least power delivery adequate for intended application of the vehicle).
 
Basketcase said:
It seems that all of the 600 - 650 cc bikes have very similar torque figures - 45 ft-lbs +/-. However the horsepower numbers vary quit a bit.
If i have two bikes with the same weight and gearing and the same torque would they have similar roll-on power. From 100 - 120 kph would they give the same kick in the pants? Would the main difference be in the top end speed? What about 0 - 60 mph times?
Click to expand...

With the same gearing they would not perform the same. You'll notice that the higher HP bike will produce it's torque peak at higher RPM, so with the same gearing, at least one of the bikes will be outside it's ideal power band when you roll on the throttle. So no, you won't get the same kick in the pants in the scenario you offered.

The main differences will be the availability of power at low RPM with the 650 and the ability to acheive greater acceleration and greater top speed with the 600 (since each one has gear ratios suited to the power profile of each engine).
 
HP sells bikes.
Torque wins races.

:)
 
Another variation is "people buy horsepower, but they drive torque".

Few people drive their vehicles with the engine high enough in the rev range to be in the peak power range a lot of the time (and if they do, their driver's license won't be long for this world, and they'll get lousy fuel consumption).

An engine tuned to make peak torque in the same RPM range where most people spend a lot of the time, and in an RPM range that coincides with normal highway speed, will feel more pleasant and not have to downshift at the sight of a slight uphill, even if when pushed to the limit it isn't ultimately as fast as one tuned for maximum horsepower. (The VW diesels are a good example of this - really good daily-driver engine, even if it won't win too many drag races).
 
Brian P said:
Few people drive their vehicles with the engine high enough in the rev range to be in the peak power range a lot of the time
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Funny....I hear them cruising through town in low gear/high rpms all the time.

Their pipes are too loud to hear me yelling "Shift you idiots!!"
 
Horsepower is a unit of measurement designed to show whether the person explaining it has any background in physics whatsoever. They teach this in high school.
 
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