Yes, torque v. horsepower is another of the black arts of motorcycling and engines. Personally, I still like my definition because it works best for bikes.
Torque is rotational force OR force applied to rotate the rear wheel (to make it push against the ground and propel us forward).
Lots of low end torque (like HDs have) makes for wonderful launch characteristics...meaning HDs should always have an advantage at takeoff. But HDs run out of horsepower quickly. That's why thier top ends runout, they don't have the horsepower to keep pushing.
A tractor and an v-twin have one important thing in common--lots of low end torque.
Remember a 600cc in line four will run in about a 11 second quarter mile. Partly because it's power to wieght is better than a v-twin but also because is makes lots more horsepower. Torque (when used in talking about bikes) is the engines ability to turn the rear wheel quickly. Once it's moving...well that's where horsepower pushes it.
There's a reason that a ZX10R will do a clean ton in first gear...and it's horsepower.
Again, when I speak to folks about torque and horsepower and bikes:
Torque is how fast you spin up, horsepower is how fast you can go. That's why you need 200+HP to be over 200mph--torque at that point means nothing to bikes. And that's why when one single slug the size of a coffee can fires the torque spins the rear wheel with so much more torque.
One of the intersting features of most scooter mag articles is the torque AND horsepower charts. They are interwined and make a big difference on how a bike rides. A bike with big low end torque goes as soon as you turn the throttle--but if it has no high end horsepower it just kinda runs out of oomph. A bike with little low end torque but tons of topend ponies will lag off the start and then turn on like it's turbocharged.
A bike like a Suzuki Hayabusa (and yes I was in possession of one for a time) makes 100ftlbs of torque and 160bhp. And my friends, it was a mind bending experience. The power is just all there all the time and...it's hard to describe.
So that's why I say: Horsepower is how much you can lift (top end) and Torque is how fast you can lift it (launching).
Personally that's why I would suggest a newbie rider try to find a bike with modest torque and horsepower. Too much torque and the bike is 'lurchy', too much horsepower and bike 'takes off at speed'.
Feel free to disagree. It's OK.
