Tech Talk: What’s a Dyno?

What is a Dyno?

Short for Dynamometer, a dyno is any device used for measuring force and power. Dynos can work in very different ways, but TTRNO’s Dynojet Dynamometer determines horsepower (HP) by calculating a motorcycle’s rate of acceleration as the motorcycle’s rear wheel spins a 500 lb roller. After the HP of the motorcycle has been determined, the dyno’s computer can measure the RPM of the engine and use the equation, HP = (torque x engine RPM)/5252, to determine the torque.

What is Horsepower?

Okay, let’s backtrack. It was the late 1700s when James Watt needed a way to express how powerful his new steam engine invention was. Because the steam engine was a replacement for horses, it was a no-brainer to use them as a benchmark. Mr. Watt observed that horses would walk 144 revolutions/hour in the typical mill-grinding, 24 foot circle, pulling a force of 180 lbs. This meant that a horse was traveling roughly 181 feet per minute, multiplied by 180 lbs of force, and rounded a bit… TaDaa we have our calculation: 1 HP = 33,000 ft-lb/min.

What is Torque?

Now that we have horsepower down, let’s take things further. Horsepower is a product of torque. Say your TTRNO Master Technician, Guy Hayes, is installing the rear axle nut on your motorbike to 170 ft-lbs of torque. If Guy is putting pressure on the wrench but it is not moving, he is not producing horsepower but he is producing torque. Need another example? If Sisyphus was pushing a boulder up a hill and wanted to take a break, he would have to produce torque to hold it in place but not horsepower.

Essentially horsepower is torque with motion which explains the use of engine RPM and our constant (5252) in the HP calculation: HP = (torque x engine RPM)/5252. Now some people may be thinking, “what the heck is this 5252?” This number is a constant determined by one revolution of a circle or 2-pi radians. Divide 1 HP (33,000 ft-lb/min) by 2-pi radians (6.28318 radians) and we get our 5252. As we can see, this number provides the movement we need to produce a horsepower number using force determined by torque.

Our next tech talk will be explaining the specific tests that can be performed on the dyno.

To see a dynamometer in action, stop by TTRNO and let us put your bike on it!

Questions?