Join Date: May 2004
Location: Toronto, Canada
Oh boy ...
This is something that engineers understand intuitively, but non-technical people cannot seem to grasp at all.
Fundamental equation of physics: F = m A
(Force = Mass x Acceleration) - if all of the measurements are in SI units then no conversion factors are necessary. This can be rearranged:
A = F / m
Acceleration = Force divided by mass. The mass "is what it is", this equation shows that the acceleration depends on the force applied.
The equation above implies "linear" geometry; motion in a straight line. Many mechanical things, including engines and wheels, operate in a rotary fashion. Torque is a force applied in a rotary manner.
The engine makes a certain amount of torque. The torque is multiplied through the gearbox and final drive ratios (what is lost in speed is gained in force - that is how gear ratios work - if you look at maximum power output condition, the engine speed of 12,000 rpm is reduced by a factor of about 8 through the gearbox and final drive to around 1500 rpm rotation of the rear wheel - but the torque is multiplied by 8 times excluding the frictional losses).
The rear wheel converts that final output torque into a straight line force of you accelerating forward, and that is what you feel when you open the throttle.
We have not said a word about horsepower yet.
Power = Force x Speed
You can apply a torque equivalent to the engine output torque, by applying a torque wrench to the crankshaft with the transmission in gear. Of course, you cannot do this with any great *speed*. Whatever acceleration you could generate by doing this, would be over in a heartbeat.
Torque is what you feel when you open the throttle. Horsepower is what it takes to do that simultaneously with moving fast to begin with.
Torque is what it takes to get a huge load moving. A tractor-trailer, for example, has an engine with enormous torque, and it has an enormous gearbox after that, in order to be capable of getting a huge load moving. But it cannot accelerate much *at speed*.
Your bike has an engine with relatively little torque (on the automotive scale; for example my VW diesel has twice as much). But it can make that torque when travelling at a high speed, and it is in a light vehicle.
Is this understandable, or is it as clear as mud at this point?
Helibars, MRA screen, Ohlins damper, reversed shift pattern, sorted suspension, braided lines, Michelin Pilot Power, all else stock 'coz it's fast enough!