I remember having this argument on this board before.

Few people understood that torque and horspeower are different words for ways of expressing the same thing.

Power, and power over time.

This guy thinks he's right because most american (read: harley) v-twins don't do well over 5252 RPM. They become inefficient at higher RPM, so their dyno sheets show crap above that, so they make the assumption that 'torque' is more important than 'hp'.

Easy mistake for people who don't like to think very hard.

Torque and HP are different but related. Torque is a force. Horsepower is power. Torque over distance produces work. Work over time is power.

A force over a given distance always does the same amount of work. However, the power produced depends on the time required to do that work.

Torque is work, and hp is how fast you can do the work. (simply)

I'm not exactly sure what you guys were trying to say, but I don't entirely agree with the parts I marked in red.

Torque is not exactly a force, it is the normal component of a force multiplied by the distance from the point of rotation to the point where the force is applied. The torque acts in such a way so as to produce a rotation.

The statements in red about torque's relation to work are not entirely correct. Torque is not work. Torque and work have the same units (Force * distance), but in the case of work, the force is applied

*in the direction of distance*, while in the case of torque, the force is applied

*perpendicular* to the 'distance'. Since they have the same units they are easy to confuse.

As far as the original question (torque vs. hp), I would think that it's the

*power* that gets you down the road. Since motorcycles are wheel-driven, torque plays a role. But, for example, a jet's capacity to 'go' is thought of in terms of

*thrust*, which is a force. For the jet (or rocket),

horsepower = thrust (lb) * speed (ft/sec) / 550

In the case of the jet, torque doesn't factor in.

It is the

*power* that is dominant in enabling you to 'go'. In other words, your bike has the greatest capacity for acceleration when the horsepower is peaked,

*not* when the torque alone is peaked. For a wheel-driven vehicle, it's the

*combination* of torque and RPM that gives you that power.

Let's try this with your friend Paulages...

Going strictly from definitions:

acceleration = force/mass (Newton's second law)

Since the mass of your bike doesn't change (neglecting fuel consumption), we see that you get the greatest acceleration when the force is greatest. But force is related to work which is related to power via P=W/t=F*d/t. Using this, force can be written in terms of power like so; F=P*t/d.

So acceleration = power*time/(distance*mass). In terms of mathematics, "time" is 'unit time' and "distance" is 'unit distance,' mass doesn't change, so it's the

*power* that governs the acceleration of the bike. Sure, power is proportional to torque*RPM, but it has to be the

combination of torque and RPM (i.e.,

power) that governs your acceleration. (Your friend can have all the torque in the universe, but your friend ain't goin' nowhere if his RPM is zero! Thus, it's the combination that counts, i.e.,

**power**.)

(To be fair, at low RPMs, well... it's the high-torque engine that will produce the better acceleration, but only because the combination of high torque at the low RPM produces more

*power* than the lower torque engine at the same RPM.)

The following is for those who are curious where this equation comes from.

******************************************************************

The following equation (which was previously mentioned) relates hp to torque:

hp = torque*RPM/5252

Here is the derivation:

First some definitions: (

** means 'times', or in other words, multiply, / means divide.*)

work = force*distance : (the force in the direction of the distance)

torque = force*radius : (the force perpendicular to the radius)

power = work/time

hp = 550 lb*ft /s : (1 hp is moving 550 lbs 1 foot in 1 second)

circumference of a circle = 2*pi*radius

RPM = 60*RPS : (conversion between rounds per minute and rounds per second)

Here we go...

power = work/time : start with the definition

= force*distance/time : replace work with its definition

= force*(2*pi*radius)*RPS : distance is the circumference of our wheel, time in RPS

= force*(2*pi*radius)*(RPM/60) : convert RPS to RPM

= force*radius*RPM*(2*pi/60) : rearrange

= torque*RPM*(2*pi/60) : torque=force*radius

We are almost done. The above equation has the units [ft*lb/time]. But horsepower is

*550* ft*lb/sec. So we must divide what we have above by 550, and we get

**hp = torque*RPM*(2*pi/60*550) ≈ torque*RPM/5252********************************************************************