(Dave) said:I was just thinking about drivetrain ideas and was wondering why
ratcheting cranks are not seen in use.
There are multiple answers to this. First, however, you are laboring
under a false impression. They've been tried.
Quoted message said:Yes it would cost you some
weight and reliability and you would give up the ability to easily
jump the bike but I am almost sure it would improve power delivery.
How?
Bear in mind that this has been hashed out here before; claims of
benefit by the proponents of the extant variations notwithstanding,
there's never been any acceptably verifiable and validated evidence
that conclusively supports the contention that they produce any
significant benefit.
Quoted message said:I
can think of two schemes, one employing a simple independant ratchet
on each crank, and the second having a further embellishment so that
each pedal would be independently disengaged during the least
effective portion of the rotation (perhaps eight O'Clock to twelve
O'Clock ?) so that it could immediately and effortlessly be moved to
the top of the powerstroke.
Oh, bloody.
First, a ratchet mechanism allows free movement in one direction and
not in the other. Think about that for a moment. An independent
ratchet on each crank would simply allow the rider to desynchronize
the pedals, which isn't all that great of an idea. It's been tried.
The bits to do it still languish in the bottoms of junk bins at some
older packrat-owned bike shops scattered around the world. The
principal problem with the concept is that the ider must *always* lift
the crank through the non-power portion of the cycle; such an
arrangement must be used with clips or cleats, as the foot must be
able to propel the crank through the entire 360 degrees. This
eliminates the option of standing on the pedals without them both
being at the bottom of the stroke as well. Trackstanding becomes
usless to attempt.
A variation on the second idea is currently in production and under
patent, and while there is some basis for contending that the idea is,
in fact, not new (and that the patent would be indefensible if
challenged), there is zero likelihood that it will, in fact, be the
subject of any attempt to copy the device. If you *really* want one,
you can get them from the Powercranks people; www.powercranks.com, but
be prepared to pay $800 or more for the privilege of making your bike
a lot less pleasant to ride.
A third and less abusive concept which doesn't use ratcheting
mechanisms but which does speed the pedal's return to the top of the
stroke is the Rotor Crank (www.rotorcranks.com), which while not
objectionable, doesn't really seem to be much more than a fancy
gimmick in my estimation. At least is doesn't render the bike
unpleasant or infuriating to ride, as the PowerCranks or the simple
ratcheting concept does.
Quoted message said:This has all no doubt been prototyped,
tried, and abandoned back in the 60's or 70's, but what were the
results? Thanks...
The results should be obvious from the lack of them as a common
feature on the bikes in your area. In point of fact, precisely the
opposite idea, the fixed-gear bike which does not freewheel *at all*
and maintains the regular synchronized motion of the pedals, is far
more common and popular, though still far from universally adored.
--
Typoes are a feature, not a bug.
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