Todd,

I'm sorry, but you're wrong. Not all dynos measure torque. Inertia dynos cannot measure torque, as they are not equipped with with a strain gauge (which is the device that actually measures the torque). Inertia dynos simply measure the rate of acceleration of the roller, and calculate the rest.

This will likely explain things better than I ever could. This is from Dynojet's WinPEP7 software:

*Power*

*Power, in mechanical terms, is the ability to accomplish a specified amount of work in a given amount of time. By definition, one horsepower (HP) is equal to applying a 550 pound force through a distance of one foot in one second. In real terms, it would take one HP to raise a 550 pound weight up one foot in one second. So to measure horsepower, we need to know force (in pounds) and velocity (in feet per second). Our Dynojet inertia dynamometer measures power according to the terms just described. The dynamometer measures velocity by measuring the time it takes to rotate a heavy steel drum one turn. The dyno measures force at the surface of the drum by indirectly measuring its acceleration. Acceleration is simply the difference in velocity at the surface of the drum from one revolution to the next. The force applied to the drum is calculated from acceleration using Newton’s 2nd law, (F)orce equals (M)ass times (A)cceleration. Power is coupled to the drum by friction developed between the driving tire of the vehicle and the knurled (diamond shaped) steel surface on the drum of the dynamometer.*

*Torque*

*When an object rotates around a point, the object’s speed of rotation depends on both an applied force and the moment arm. The moment arm is the distance from the point of rotation to where the force is being applied. Torque is the product of the force and the moment arm. For example, if a rope, wrapped around a drum of one foot radius, is pulled with 550 pounds of force, the resulting force is 550 foot-pounds. The Torque on the dyno’s drum can be calculated by multiplying the force applied by the drum’s radius. However, engine torque is not equal to drum torque because the gearing through the drive train changes the moment arm. The change in the moment arm is proportional to the ratio of engine speed to drum speed. Therefore, tachometer readings are necessary to calculate and display engine torque.*

Please don't misunderstand my position here. I didn't intend for my statements here to be argumentative. I was just contributing some facts on the function and operation of different dynos. When the public understands how these dynos function, they can better interpret the results that they are given.

Harry