More power - a look at horsepower and torque

What is horsepower, torque and what's the difference between them? What does it mean when talking about motorcycles?
HORSEPOWER
Horsepower is abbreviated HP. It's an old measurement from the times when the biggest equipment humanity had were horses and oxen.
So what is a horsepower? That depends on whom you ask and how it's being used.
Horsepower, in a motorcycle, is in several areas:
  • Brake HP. The net mechanical energy put out by the crankshaft.
  • Effective HP. This is how much of the power is turned into actual work. Some power is lost to friction, heat and our inability to make anything 100 percent efficient.
  • Nominal HP. Engine size, piston speed measured at 7 psi.
  • Indicated HP. How much power the engine can put out when losses to friction are figured.
  • SAE. This is an American measurement of just a running motor. Nothing attached to it.
  • HP DEFINED

    The Machinists' Month Journal Vol. 22 from 1910, took a serious look at HP. The author compared HP to the amount of work an average horse can do. Then, the Journal compared that to what a mechanical horsepower does. "A standard horse-power is the amount of energy that will raise a weight of 33,000 pounds one foot high in a minute or 550 pounds one foot high in one second."
    Putting that in motor terms, the Journal says, "An engine or motor exerting one actual horse-power will raise a weight of 10 pounds 3,300 feet in one minute, but will require 10 minutes to raise 330,00 pounds one foot high." So when a motor's HP is figured, "one mechanical horse-power is therefore equivalent to the work of four horses," according to the publication.
    Whew.

    WHAT DOES HP MEAN TO A BIKE

    What does this mean to a motorcycle? Not much. All the HP definitions above really don't matter because they leave out so much where a motorcycle is concerned. The first, and literally the biggest factor left out is the weight of the motorcycle. That engine and drive train first has to push the bike. That's tires, a gas tank, exhaust, forks and everything else. The second biggest factor is the person in the saddle. More weight to be pushed.
    A 10 HP motor, when geared right, is enough to move a 110-pound person and a 250-pound person. The 110-pounder is going to move faster than the 250-pounder when the same gearing ratio is used.
    HP does not tell you how fast a bike can go. It's only a rough guide to how much it can do depending on the weight load.

    TORQUE MATTERS

    On a motorcycle, power is best described in torque. What is torque? Specifically, it measures how much power is used to twist something. Think torque wrench.
    Twist is important. Wheels have to spin, which is twist. The motor converts the up and down action of the pistons to twist, turning the various parts that turn. Here's a cool gif showing the twist that pistons generate.
    In this regard, HP is important. More horses mean the twisting can be done faster, depending on the gears, and more can be twisted.
    Most bikers look at torque in terms of speed. With that as the criteria, torque in a motorcycle is how fast it accelerates. So, think of torque as RPMs.

    FAST ACCELERATION

    So why do sport bikes, with smaller motors, accelerate faster than cruisers or street bikes with bigger motors? Certainly weight is a factor. But the biggest difference is the RPMs. Sport bikes have a short stroke of the piston. Things turn (twist) faster. These short strokers do sacrifice brute power for acceleration. That's why you never see the fast sport bikes pulling trailers.
    We can measure our rides in all kinds of ways. The only measurement that really matters is - do you like your ride? Get on it and ride.

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