It happens over and over again, in garages, shops, dealerships, and bars-guys going back and forth with each other, bragging about how much horsepower their bike just put out on the dyno. People are always telling me how their bike just gained 2-3 hp by a simple tweak, or more often than not, the addition of new components to the motor. Quite often when I hear a conversation such as this I might fire a few questions back at the perpetrator, inquiring about things such as engine size and type, what kind of bike the motor's in, and what type of riding they normally do.
While these questions might seem inconsequential at first, they certainly shed some light as to how those horsepower numbers equate to performance for a particular type of motorcycle. In many cases these big numbers seem to be impressive when taken out of context, but when looked at in the bigger picture they may only tell part of the story. When it comes to performance, so many riders are concerned with horsepower that they often overlook the torque curve generated by the dyno's software. Know it or not, torque is the main reason Harley-Davidsons are so much fun to ride. In a properly set-up motor the torque curve should be tall and linear, delivering the majority of torque in the rpm range in which you do most of your riding.
Many (if not all) Harley riders began on a motorcycle other than a 45-degree V-Twin. Riding a motorcycle of a different persuasion can certainly be a lot of fun as you pull long and hard on the throttle, getting the motor to spin in the vicinity of the redline-usually somewhere in excess of the 10,000-rpm range. Well, that's a perfect illustration of horsepower: running a motor right up to its limits, flat-out. The problem with many of these types of motors is that they generate much less torque as a percentage when compared to the horsepower numbers. While it's fun to be riding on the edge now and then, it seems Harley's approach makes much more sense-come up with a motor that will create relatively equal torque and horsepower numbers.
Who can forget the very first time they rode a Harley? The feeling is like nothing else. Grabbing lots of throttle in pretty much any gear launches the bike forward over a broad rpm range-now, that's torque. There's no reason to constantly bang the shift lever up and down through the gears to keep the bike accelerating to your liking.
If you ride a street bike as most of us do, you should look for a combination of components that will give you a good, strong torque curve in the middle of the rpm range. Not at the top, not at the bottom, but in the area where you do the majority of your riding. Building or modifying a motor to suit your particular needs should be done with reality in mind, not superficial numbers. These days baggers are very popular motorcycles. They weigh in at somewhere between 730 to 800-plus pounds dry. Add to that a full fuel load, a couple of passengers, and some gear, and you're tipping the scales to the tune of 1,100-1,200 lbs. That's a whole lot of weight. You're not going to move that with horsepower alone; you'll need the low-end grunt provided by the torque characteristics of the motor. When was the last time you tried to pass a line of cars with the motor bouncing off the rev limiter? Not lately, I'll bet. Chances are far better your tach was hanging in the 2,800-4,800-rpm range as it should be.
Now, don't get me wrong here-I like busting my buddies' chops about how much horsepower my motor puts out as much as the next guy. But when it comes right down to it, unless I'm looking for a dyno crown or racing down a dragstrip, these high horsepower numbers are just numbers, and nothing more.Be well.Steve