Doug5150

It's my belief that a system that allows for variable leg-stroke would be at least very much more comfortable to use than conventional pedals, and I intent to build one at some point in the future. It would also be heavier, but that doesn't mean it wouldn't be more useful. A single-speed bike is lighter than the same bike with a geared hub, but most adult bikes bought for recreation (in first-world countries at least) have gears, because people think that the ability to match the pedaling load somewhat to their preferred exertion level is worth hauling around a couple more pounds of metal for.

If you consider the leg extensions people use while jogging, they start out taking rather long strides, then take shorter strides as they get tired. They take moderate strides on level ground, tend to take shorter strides going uphill, and do "lunges" up stairs, skipping one or more stairs. They do not use the same leg extensions all the time, because it's not comfortable or natural to do so. The fact that many bicycles have gears does not address the problem of the same leg extension always being used.

A bicycle with conventional cranks forces you to use the same exact leg extensions all the time. Most casual riders don't tweak their crank lengths to perfection, cranks don't come in a wide-enough variety to even suit the general population and even if you could make adjustable-length cranks that could change length on the fly, you'd still have the problem of the leg-extension to seat distance.

I would also point out that many of these lever-systems are not levers at all but treadles, which are just fixed by connecting rods to a conventional crank setup, and don't benefit from variable-length pedal strokes at all. The only advantage these can claim is a pedal surface that doesn't move fore-and-aft as much as a pedal on conventional cranks would.
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