Dynamometer Myths, Facts, and Frequently Asked Questions

What is a dynamometer?
*A dynamometer, or dyno as it's normally called, is a machine used for testing of vehicles in exacting and repeatable conditions.
*With a dyno you can run a motorcycle at nearly any speed and measure the computed horsepower by how hard or fast it spins the drum inside the dyno.

What is tuning?
*An engine runs best with a correct ratio of air to fuel called stoichmiometric mixture.
*That mixture is generally between 13.2 through 14.7 parts air to 1 part fuel.
*When the motorcycle is running on the dyno the exhaust gas is analyzed to determine if the mixture is correct.
*Too much fuel and the mixture is "rich" and too much air and the mixture is "lean".
*A motorcycle can be lean at some RPMs and /or throttle positions and too rich in others.
*Changes are then made to the motorcycle's fuel injection or carburetors to correct the fuel ratio and thus obtain the most potential from the engine.

Why is the air/fuel ratio so important?
*Your engine is essentially an "air pump".
*Ideal and theoretical numbers are derived for your bike for it to run its best.
*If your bike is running too lean or rich, you risk not only poor fuel mileage, but catastrophic and costly motor damage.

How is the motorcycle tuned?
*On a carburetor, changes are made by replacing or adjusting parts of the carb.
* Parts like jets and needles that control the flow of fuel can be replaced or modified with a "jet kit".
*Fuel injected bikes can be modified with a Power Commander (or similar) or replacing the stock computer.

How does a Power Commander work?
*Inside the computer of fuel injected motorcycles is a "fuel map".
*At given throttle positions, RPMs and other factors like air density and temperature the computer uses the fuel map to tell the fuel injectors how much fuel to spray into the engine.
*When changes are made to the motorcycle that effect the amount of air the engine uses (like an aftermarket exhaust or air filter) then changes to the fuel map need to also be made.
*A Power Commander intercepts the signal going from the computer to the injector and modifies it to add or subtract the right amount of fuel to make the appropriate air / fuel ratio.

Do I need a custom map?
*There are a lot of downloadable Power Commander maps that will allow your bike to run fine - but they are designed in a laboratory in Arizona - "close" isn't the same as "best".
*Just as off-the-rack clothing of the same size may not fit just right, custom tailored clothing is made exactly to your size.
*Every bike is a bit different so not every map fits every bike.

Does dynoing hurt the motorcycle?
*No more than riding it on the road does.
*In fact, if something is wrong with your bike, it is safer and easier to diagnose on the dyno.
*Be sure your bike is in good working order: recent service, no oil leaks, no fuel leaks, everything is securely mounted, etc.
*We inspect the chain / belt and tires in addition to an overall inspection-
*If we feel it’s unsafe, or a hazard to run on the Dyno we won’t run it. Safety first.

Will my bike overheat on the dyno?
* No. Cycle Stop boasts an extremely well force-ventilated space and high-powered fans to keep your bike cool.
*We also monitor your bike's engine temperature closely.

Will the Power Commander void my warranty?
*In most cases, in order for the manufacturer to deny warranty for a failed component, they must prove that the aftermarket part caused the component to fail.
*As the Power Commander cannot send current to the stock ECU, it is highly unlikely that it could damage the stock system in any way.

My dealer says my warranty is void because because I installed aftermarket parts on my bike. What can I do?
*Consumers have specific rights on any product they purchase.
*SEMA (Specialty Equipment Market Association) helps protect these rights
and has a web page with a list of what to do if your warranty is denied. For more information please visit:

Crank hp vs Rear wheel hp.
*Many people are confused between the two methods of reading hp.
*Crank hp is what most manufacturers state in specifications. It is derived with a motor bolted directly to a dynamometer.
*Rear wheel hp (rwhp) is what most dynos read.
*rwhp is lower than crank hp due to drivetrain loss from transmission gears, chains, tires and wheels.
*Drivetrain loss usually is about 15% but can vary from bike to bike.
*Cycle Stop dyno maps show rear wheel horsepower.

Why are dyno readings between dynos different?
*Horsepower is a computed figure based upon how much torque an engine produces.
*The torque of the motor is measured on a dyno by how quickly it can rotate a drum of a given weight.
*Several variables like bearing wear, lubrication, temperature, etc can effect how easily or hard the drum can be rotated thus skewing the torque reading of different dynos or even the same dyno on different days.
*An eddy current dyno produces more repeatable and consistent results by controlling the speed of the drum that the motorcycle is turning.
*The DynoJet 250i also samples air pressure, temerature and humidity within the room.
*It uses this data to apply a "correction factor" to the computed data.
*Since engines generally run better in cooler air with less humidity the motorcycle run at different times could show different output readings.
*The correction factor ensure that the operator is comparing "apples to apples" when looking at runs from different times.

Tim Miles
Knoxville, TN