Torque vs Horsepower

[Hossamania]

All true; but do a top gear roll-on at 55-65 and the equation isn't nearly so lopsided... The Big Twins,especially heavy ones, will never outrun the crotch-rockets; however, for geriatrics like me who don't really like rowing the gearbox, torque is a big deal...

Oh hell yes, you'll get no argument from me about that! I much prefer a motor with lots of bottom end, not picky about what gear it's in, and not having to be run at it's power peak in order to move the bike. Just twist the throttle from low rpm and go, that's the way I like it. I wouldn't be riding HD's if I felt otherwise, believe me.

My whole point is that when it comes to maximum acceleration, it's the power number that matters, not the torque number.

Just to make it even more complicated than it is already, it's actually "applied force" at the contact patch that matters. The components of that are engine torque at a given RPM, final drive ratio, and drive-wheel radius. By the way, I spent a lot of time developing and playing with a calculator that determined best shift RPM for a given setup (based on applied force as mentioned above, and assuming no tire slippage). Turns out, it's almost always at or very near redline, contrary to what many think.

I knew a guy that thought he was pretty savvy with motors, tuning, and racing. He wasn't. He had an '01 twin cam built to 95", and set his shift light at 5250 rpm's, even though it made good power to 6200, because he thought that was the best shift point, since that is where horsepower and torque crossed on the dyno. He figured the motor would produce the best power into the next gear. I started explaining that that was just a reference point for power to be measured and compared, not necessarily where the most power was made. I then explained that crotch rockets make max horsepower at about 14,000 rpm's, but that their dyno graph also crosses at 5250 rpm's. Did he think that was an optimal shift point for that motor also, leaving 7000 rpm's of power on the table? He really didn't have an answer for that one.
So, I said let's go test your theory. We'll roll 2nd gear, both engines will be pretty even at that point, both being 95" and built similarly. He can shift at 5250 rpm, I will go to 6100, and let's see.
Well, of course you know what happened. I pulled away from him hard, let him catch me in 3rd, then just wailed on it and never let up.
I still don't think he got it. But he didn't like me much after that, and I was quite ok with that.
He did have a tach the size of a dinner plate on his Heritage Springer, with the shift light. Looked dopey as hell.