How does an elliptical machine measure speed?

Ellipitcals measure flywheel rotations, not distance, but there is a rough way to estimate distance as if walking.

1. Rotate one pedal until it has achieved its most rearward position without starting forward again. Do use the pedal and not the flywheel. The wheel rotates in a circle, but the pedals rotate in an elipse with a greater maximum change in forward/backward distanc than the diameter of the flywheel.
2. Position a ruler or stick vertically at the pedal's front, the bottom of hte ruler/stick marking a place on the floor.
3. Rotate the pedal until it reaches its most forward position, and mark that point as well.
4. Measure the distance, which is actually the estimated distance travelled in on half of a flywheel rotation.
5. Multiply the figure by two to get the distance for a full rotation.

Now you have a ROUGH estimate of linear distance traveled in one rotation -- but at WALKING SPEED (more on this later). You can use this to calculate how many rotations are necessary to travel say a mile. Example: my elipical has a linear distance per "step" of 17.5 inches, which means 35 inches per two steps or one rotation of the flywheel. A mile has 63,360 inches.(1 mile = 63,360 inches) hence: 63,360 / 35 = 1810 rotations = 1 mile

(1 km = 39,370 inches) hence: 39,370 / 35 = 1125 rotations = 1 km

The Problems of Thrust/Inertia and SpeedWhen actually jogging or running, your stride length elongates and your thrust and/or interia increases. There are split second instances where both feet are off the ground while running, and you travel forward a little farther than your actual stride length. This cannot be accounted for on an ellipical. There are complicated equations that can estimate this, but they aren't really necessary. Rough judgment will be adequate and give you fewer headaches. I use the following to modify Rotations per Target Distance at subjectively labelled speeds.Walking: 100% x rotations

Jogging: 90-95% x rotations

Running: 80-85% x rotations

Sprinting: 65-70% x rotations

Other people may have different opinions on change of stride length and interia/thrust. The two points relevant here are:

1. there's no way to be certain.
2. we're only looking for an estimate.

With these figures, you can even break down your target rotations (estimated distance) by how much time you spend at particular subjective speeds. You can use this to plan out a regime of speed changes after a certain number of rotations given a target distance you wish to "travel." Or, if you can remember the rotations per speed change you made in a session, you can back track through an figure the rough overall distance you travelled.

In the end, it doesn't really matter that much. Putting in the time at your own pace for your health is what it's all about.

--J.C. Hendee