Thoughts On Dynos…
A chassis dyno is used to produce a report of horsepower and torque. It consists of a load device, a set of rollers in contact with the vehicle drive wheel, and several measuring and control mechanisms.
They are generally of two types: An Inertia dyno, which utilizes the inertia of a rotating drum of known mass to resist the force of the engine being measured, and a Load-Control dyno, which uses a precisely-variable mechanism to apply the resistive force.
That’s what it is and does, but how does a dyno actually work? How can it measure engine horsepower without knowing the final drive ratio, for instance? And tire diameter? And how can it determine engine horsepower unless it also can determine drivetrain losses? The more I thought about that, the more confused I became. So I thought about it some more.
Here’s where I am now.
NOTE: I've attached a couple of additional files that I thought might be of interest. "True Horsepower" was created by a dyno vendor, and could therefore considered to be somewhat biased, but it is also informative, in a pissed-off sorta way. The "Cycle Canada" article addresses some of the same issues. Both of them contain some answers to some of the questions I posed in "How Dynos Work". For those who still believe the "back-to-back" tests in Harley magazines and the power numbers quoted on internet forums, they may also be informative (?)