RaWarrior
Well-Known Member
This seems to be a topic that springs up fairly often around here and can be sort of tough to explain, in terms of how it relates to actual performance. I've heard some good explanations and some lousy ones and there tends to be a lot of misconceptions about it. From hanging around go-fast types for a while, as well as college mechanical engineering classes, I think I've got a pretty good grasp on it and an explanation that's easy to digest, so to speak.
First, freshman physics lesson. Torque is a measure of rotational force. 10 ft/lbs is equal to the force applied to a pivot with a 10ft pole with a 1lb weight hanging at the end, or a 10lb weight on a 1ft pole. Torque is equal to the force times the length of the lever...you can trace it back to the pin's offset of the crank(the "lever", or moment arm) and the "force" is the compressive force in the rod, to put it simply. Torque can be multiplied through gearing. Work is a function of a force times displacement(distance).
Power is the derivative function dw/dt, or "change in work over change in time". Since time is the denominator, lower times and/or higher work result in more power. Horsepower is a unit of power, or about 33,000 ft/lb/min (displacement*force(gravity)*time). As such, power cannot be multiplied. Gearing alters the balance between displacement and time. Using a low gear increases force, but also decreases displacement(revolutions) and time by a proportional amount, so overall output is unaffected. Transmissions are just to cater to the internal combustion motor's natural shortfalls, limited RPM and a rising power curve, why most electric vehicles don't have transmissions....they don't need them.
Think of torque as "how much work a motor can do", and horsepower as "how quickly it can do it". Motor 1 has 50hp and 25 ft/lbs of torque. Suppose motor 2 has 25hp, but 50 ft/lbs. Let's say motor 1 lifts 500lbs a certain distance in 10 seconds. Then motor 2 lifts 1000lbs in 20 seconds. Without gearing, #1 could not lift #2's load. In order to, it would need a 2:1 reduction, to output 50lbs at half the speed. So now it can lift twice as much, but in twice the time. Suppose a third engine, with 25hp and 25 ft/lbs of torque. It would also need a 2:1 reduction, but due to it's lower power, would need 40 seconds to lift 1000lbs. And a fourth, with 50hp and 50 ft/lbs of torque. It can lift 1000lbs without reduction, but since it has twice the horsepower of #2, it can do it twice as quickly, lifting it in 10 seconds.
Now that's a very simplified example but it gives you the idea of the relationship. Imagine the "weight" is your bike, and the "lift" is acceleration.
So how's that translate to bike performance? Again, to make things simple, lets take three general examples.
A 600 class sportbike puts out 100hp and 40 ft/lbs of torque
A Vmax puts out 120hp and 80 ft/lbs of torque.
A M109 puts out 100hp and 125 ft/lbs of torque.
Now if you lined those three up, which would win? Torque or HP? Most likely, it would be that torque wins off the line, but horsepower runs away with it. From experience, that's the case taking my Vmax against a M109. It gets the jump right off the line(I have a Venture diff), but I reel it in by the end of second and walking by it in third. The reverse is true from experience with an R6. It doesn't have a whole lot of torque, and isn't that quick off the line. I'll gain a decent lead, but by 60 or so it's closing the gap, and by 80-90 it goes by me. While that doesn't totally fit with the example, it's lighter weight and better aerodynamics make it happen. But the trend is clear....torque gets things moving, and horsepower keeps it going. Of course there's a lot of other factors...weight namely, but also power curves of the motor, gearing, traction, ect. But boiled down to just output, that's the general trend.
Why is that? Since torque can be multiplied through gearing, motors that start with more torque have more to be multiplied, so the transmission can be more of an advantage, at least initially. This makes them very quick off the line, while this advantage lasts. After a couple shifts, the mechanical advantage diminishes. Now it's up to the power "do the work quickly" instead. The Vmax has more power, so even with considerably less torque, it pulls ahead. The Vmax can't do as much work as the cruiser, but what it can do, it does faster.
So ideally you want both....to be able to do a lot of work very quickly....but that isn't always the case. So pick your races accordingly. The Vmax is a good balance of a V's torque and a four cylinder's horsepower, so to a point you get the best of both worlds.
I dunno...hope this helped people understand the relationship.
First, freshman physics lesson. Torque is a measure of rotational force. 10 ft/lbs is equal to the force applied to a pivot with a 10ft pole with a 1lb weight hanging at the end, or a 10lb weight on a 1ft pole. Torque is equal to the force times the length of the lever...you can trace it back to the pin's offset of the crank(the "lever", or moment arm) and the "force" is the compressive force in the rod, to put it simply. Torque can be multiplied through gearing. Work is a function of a force times displacement(distance).
Power is the derivative function dw/dt, or "change in work over change in time". Since time is the denominator, lower times and/or higher work result in more power. Horsepower is a unit of power, or about 33,000 ft/lb/min (displacement*force(gravity)*time). As such, power cannot be multiplied. Gearing alters the balance between displacement and time. Using a low gear increases force, but also decreases displacement(revolutions) and time by a proportional amount, so overall output is unaffected. Transmissions are just to cater to the internal combustion motor's natural shortfalls, limited RPM and a rising power curve, why most electric vehicles don't have transmissions....they don't need them.
Think of torque as "how much work a motor can do", and horsepower as "how quickly it can do it". Motor 1 has 50hp and 25 ft/lbs of torque. Suppose motor 2 has 25hp, but 50 ft/lbs. Let's say motor 1 lifts 500lbs a certain distance in 10 seconds. Then motor 2 lifts 1000lbs in 20 seconds. Without gearing, #1 could not lift #2's load. In order to, it would need a 2:1 reduction, to output 50lbs at half the speed. So now it can lift twice as much, but in twice the time. Suppose a third engine, with 25hp and 25 ft/lbs of torque. It would also need a 2:1 reduction, but due to it's lower power, would need 40 seconds to lift 1000lbs. And a fourth, with 50hp and 50 ft/lbs of torque. It can lift 1000lbs without reduction, but since it has twice the horsepower of #2, it can do it twice as quickly, lifting it in 10 seconds.
Now that's a very simplified example but it gives you the idea of the relationship. Imagine the "weight" is your bike, and the "lift" is acceleration.
So how's that translate to bike performance? Again, to make things simple, lets take three general examples.
A 600 class sportbike puts out 100hp and 40 ft/lbs of torque
A Vmax puts out 120hp and 80 ft/lbs of torque.
A M109 puts out 100hp and 125 ft/lbs of torque.
Now if you lined those three up, which would win? Torque or HP? Most likely, it would be that torque wins off the line, but horsepower runs away with it. From experience, that's the case taking my Vmax against a M109. It gets the jump right off the line(I have a Venture diff), but I reel it in by the end of second and walking by it in third. The reverse is true from experience with an R6. It doesn't have a whole lot of torque, and isn't that quick off the line. I'll gain a decent lead, but by 60 or so it's closing the gap, and by 80-90 it goes by me. While that doesn't totally fit with the example, it's lighter weight and better aerodynamics make it happen. But the trend is clear....torque gets things moving, and horsepower keeps it going. Of course there's a lot of other factors...weight namely, but also power curves of the motor, gearing, traction, ect. But boiled down to just output, that's the general trend.
Why is that? Since torque can be multiplied through gearing, motors that start with more torque have more to be multiplied, so the transmission can be more of an advantage, at least initially. This makes them very quick off the line, while this advantage lasts. After a couple shifts, the mechanical advantage diminishes. Now it's up to the power "do the work quickly" instead. The Vmax has more power, so even with considerably less torque, it pulls ahead. The Vmax can't do as much work as the cruiser, but what it can do, it does faster.
So ideally you want both....to be able to do a lot of work very quickly....but that isn't always the case. So pick your races accordingly. The Vmax is a good balance of a V's torque and a four cylinder's horsepower, so to a point you get the best of both worlds.
I dunno...hope this helped people understand the relationship.
