Difficulties With Our "Drum"

Our trusty SuperFlow Cycledyn dynometer – the one we run all our testbikes on to determine rear wheel horsepower and torque – has started acting up. In an effort to locate the problem we pealed the panels off, revealing the dyno’s internals. Ever wondered how one of these machines works? Here’s a summary.

The bike’s rear wheel spins a large drum (bottom right), which is coupled to an electromagnetic brake (left) that measures and matches the output of the motor being tested. A strain gauge mounted to the brake measures torque, while a pickup on the bike’s ignition system measures engine RPM. Those numbers are then crunched to determine horsepower using the equation torque x rpm / 5250.

Our dyno calculates data every 100 rpm from a point just above idle all the way to the rev limiter. That info is then plotted in a graph for quick comparisons and also populates a chart that we use for more careful analysis of a bike’s power output.