Originally Posted by
greybum
Just wondering if it affected hill-climbing?
[Sitting] DF riders "rock" while doing hills - I think "rocking" allows them to keep a more constant velocity between pedal-strokes - improving their efficiency during the climb. Going up hill, if we slow-down between strokes, we speed-up (accelerate) on the next, and energy is required - lost - just to accelerate,
in addition to the work required to go a few feet up hill. Does an elliptical chain-ring help keep a constant velocity going up hills?
"Rocking" example:
http://www.youtube.com/watch?v=OzIxObE2A0U
The "rocking" of any sort or direction on a DF is to try to use more gravity and less leg muscle. The more tired the rider's legs are, the more creative ways you're going to see of them trying to keep the pedals going around.
Elliptical rings increase the chainring size when you have the most power, and decrease it when you have the least. That's their purpose. The most important part of this effect is that the ellipticals make it easier to get through the dead spot. There is no quantitative data for this, but I believe the biggest gear you can turn over is what you can get through the dead spot. When the dead spot gear inches are reduced, you can turn a higher than normal gear through the power spot.
Ellipticals don't smooth out the stroke, in fact, they do the exact opposite. For the same ground speed, when the elliptical approaches the large diameter of the ring, the crank speed slows down. As the ring then passes the large diameter and rotates toward the smallest diameter, the crank speed increases. For the entire pedal rotation, the foot speed is constantly slowing and speeding up. It's noticeable at first, but you quickly get used to it. The more exaggerated the ellipse, the more of the change in pedal speed. Some people have knee problems if the pedal speed change is too much because as the pedalsslow for the high spot, the loading also increases, which can be too much for some knees. The ellipticals are most noticeable for people with bad technique who grind because the acceleration and easing through the dead spot is most noticeable. Ellipticals can help anyone though and the benefits are not diminished with proper pedal technique. While the power output using round rings during a complete pedal rotation would produce something like a sine wave with the actual pedal speed looking like a relatively flat/straight line, using elliptical rings would still produce a power sine wave but the peaks would be longer while the valleys would be shorter. At the same time, it would change the pedal speed line from pretty much flat, to a sine wave also.