Touring Tip: Motorcycle Performance Metrics

Jun 05, 2015 View Comments by

Touring Tip: Motorcycle Performance MetricsPart 1: What’s Horsepower Got To Do With It? 

It seems that almost every month or so a new motorcycle model is crowned king of the horsepower hill. For many years, manufacturers have been competing for consumer dollars based on the published performance statistics of their various models. In addition, consumers are bombarded with a dizzying array of performance metrics, including wet weight, dry weight, torque, 0-60 and quarter mile elapsed times, etc.—but the most prominent statistic usually quoted is horsepower. But what are horsepower and its performance sibling torque, how much power does a touring bike need, and what other performance criteria are important for touring?

Touring Tip: Motorcycle Performance MetricsWhat are Horsepower and Torque?

In the early days of automobiles—or horseless carriages as they were initially called—it seemed only natural that the power output of these new fangled machines would be expressed in relation to the amount of work that the most commonly known and used source of motive power was back then—a horse. The generally accepted definition of one horsepower is the energy it takes to move a 330-pound object 100 feet in one minute.

Torque, which is a component in the horsepower formula, is the twisting force that rotates an object (e.g., a crankshaft). Torque is usually quoted in pounds-feet, which is the force measured in pounds pushing on the end of a lever measured in feet.

Horsepower is calculated by a formula that includes units of force produced (torque) and how fast that force is applied (RPM). As a result the amount of torque and horsepower produced by an engine varies, depending on the RPM at which the engine is spinning. Single horsepower and torque specifications quoted for motorcycles are usually the maximum amounts produced over the motor’s entire RPM range. (OK, I know this is getting a little technical and if your eyes are starting to glaze over, feel free to skip the next two paragraphs.)

Generally there are two ways of measuring horsepower and torque: at the crankshaft (aka “brake horsepower”) or at the motorcycle’s rear wheel. The difference in the two measurements is the amount of power lost through the primary drive mechanism, which can be a chain, belt or driveshaft. Different bikes will vary, but horsepower loss of around 10-percent is a rough rule of thumb. A bike with a driveshaft, though, usually will lose more power between the crankshaft and the rear wheel than one with a chain drive. Manufacturers usually quote horsepower and torque figures measured at the crankshaft. Independent bike tests, however, usually report power output measured at the rear wheel on a dynamometer. Obviously, power delivered to a bike’s rear wheel is what really counts out on the road.

Some motors are designed to produce their maximum power at high RPMs (e.g., sport bikes with in-line four-cylinder engines), while others reach their peak power at lower RPMs (cruiser V-twins) and still other engine designs are usually somewhere in-between. From a seat-of-the-pants perspective, a rider feels power building as RPMs increase, but the motive force of engines with a high level of torque at low RPMs will be felt almost immediately, with a twist of the wrist, but then may quickly drop off.

How Much Power is Enough or Too Much?

The level of power a motorcyclist needs for his or her mount is a function of the vehicle’s total weight (motorcycle, rider, passenger, riding gear, and luggage) and the cruising speed and acceleration capabilities desired. The more weight there is to be pushed down the road means that more power will be required. But a touring bike may perform best with a different power delivery profile than some other types of bikes. For a heavily loaded, full-on touring bike, torque may be more important than total horsepower.

With manufacturers posting higher and higher power ratings for bikes across their product lines, riders may wonder if there is ever such a thing as having too much power. I define too much power (at least for me) as a level that is substantially in excess of that needed for riding safely on streets and highways. Perhaps most riders would say that their mount can never have too much power, but this is a question each rider will have to answer for himself or herself.

Next month we’ll focus on the important performance parameters for touring motorcycles.

 

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