eccentric cranks ?

avronb

Pedelecer
Oct 8, 2011
97
0
Watching the Tour De France i noticed some of the cranks appeared to be not round,if so what are the advantages of this set up.
 

flecc

Member
Oct 25, 2006
53,128
30,555
It's the chainwheel that is eccentric, Bradley Wiggins being one who likes them.

The purpose is simple, the small diameter sections are with the cranks at the top and bottom which means the chainwheel and cranks are taken rapidly through those non-productive parts of the rotation at a given road speed. i.e. lower geared so higher cadence at those points.

That also means the larger diameter chainwheel sections are at the top (and bottom) of rotation when the cranks are horizontal. Since that's where the rider exerts the maximum leverage, the advantage is effectively a momentary higher gear at the point of maximum leverage in each crank stroke, imcreasing rider strength utilisation.

The disadvantage is the irregular speed of rotation within each revolution, something only some riders get on with.
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jazper53

Esteemed Pedelecer
Jan 20, 2012
890
18
Brighton
It was a Shimano invention 'back in the day'..

Biopace - Wikipedia, the free encyclopedia

was also on the first bike that I imported from Canada when I first got into MTB's. I was fit then so not sure it made a whole heap of difference ;-) Still have some spares in the toolbox ;-)
It seems a great idea, giving a slight relief on higher gears, without having to change down so much.
 

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