What's a Compact Crank, anyway?

[DebW]

but why are we calling a chainring or gears a crank? I am confused.

A crank consists of chainrings, spider, and pedal arms. Because you need different spider arms with a different bolt circle diameter for a triple, double, or compact double, the chainrings aren't interchangeable. And the right pedal arm attaches to the spider. So you need the whole shooting match to switch from one to the other, ie, you have to replace the crank.

[mimitabby]

so the gizmo that the pedal sits on is NOT a crank, it's a pedal arm?

[DebW]

so the gizmo that the pedal sits on is NOT a crank, it's a pedal arm?

You can say that the pedals are attached to the crank, because the pedal arm is part of the crank. The arm, spider, and chainrings go on and off the bike in one unit, collectively called "the crank".

[mimitabby]

You can say that the pedals are attached to the crank, because the pedal arm is part of the crank. The arm, spider, and chainrings go on and off the bike in one unit, collectively called "the crank".

Thank you Deb, you are making sense to me. So what about a short crank?
there was a thread just a little while ago about a short woman wanting a short crank. for that matter, the average woman IS shorter, should women's bikes have shorter cranks, and is that a big problem?
(Do they sell them?)

[DebW]

Thank you Deb, you are making sense to me. So what about a short crank?
there was a thread just a little while ago about a short woman wanting a short crank. for that matter, the average woman IS shorter, should women's bikes have shorter cranks, and is that a big problem?
(Do they sell them?)

You are full of questions today, Mimi. I suppose I should add that a crankset includes the left crank arm as well. A short crank means that the arms are short, sized to match a smaller person's leg length. Crank arms come in 165, 170, and 175 mm and maybe some in-between lengths. So yes, a well-designed woman's bike would have 165 mm arms matched with smaller frame sizes, 170 mm arms for larger sizes. A good fitter would determine the proper crank arm length independent of frame size. Crank arm length has nothing to do with the chainring size or gearing per se, but of course a longer crank arm gives you more leverage for turning over a bigger gear.