Originally Posted by
Leisesturm
Leverage is leverage. Torque is torque. A longer lever will allow the same rider to push the same gear through TDC with greater perceived "ease" than a shorter lever. This is not debatable. It is why you use a 14" crescent wrench on a frozen bolt and not an 8". If you just want to spin a bolt around then the 14" is going to be unwieldy and you will get much better results twirling a loose bolt with a much shorter wrench. When using shorter cranks you must gear down, and when you do so, of course the gears will be easier to spin, they are lower gears. And you seem to think that shortening cranks raises cadence in and of itself. They do not. They require increased cadence if you are going to keep up with your riding buddies. A cadence of 100RPM will be easier to maintain with shorter cranks than longer ones but you still have to be willing to go there. Also there are plenty of riders, this one included. That are well able to spin "normal" cranks well in excess of 100RPM. And 100RPM is still 100RPM. Just because the cranks are shorter doesn't make it the same thing as a longer crank at 60RPM. Its still a big deal.
Leisesturm, where are you coming from?
Are you an industry insider?
I'm 5'2" with a long torso and short legs. I have owned and ride many km's on bikes with, 110mm cranks, 125mm cranks, 135mm cranks, 140mm cranks, 152mm (6") cranks, 165mm cranks and 170mm cranks. I've ridden bikes that have seat tube angles from 69 degrees to 78 degrees.
When I say that I haven't lost power from shorter cranks, this isn't just theory to me. 110mm cranks probably are a little short, but still WAY better for me than 170mm cranks. When I say that longer cranks make it harder to get through top dead centre, I know from personal experience that this is so. My torque delivery with 165mm and 170mm cranks is VERY choppy. With 125mm and 135mm cranks I can feel the extra torque that I can deliver through the whole stoke.
When I was riding on 165mm cranks and a seat tube angle of 75-78 degrees I couldn't use the drops to save myself. My knees rose into my chest and I couldn't bear my weight on my hands (I do have weak arms and hands). With 125-135mm cranks and a seat tube angle of 70 degrees or so I have NO problems riding along in the drops. in fact I find it comfortable.
And the cold hard truth is, I haven't developed anything new at all. I've owned and seen numerous small vintage bikes that are EXACTLY the same as what I recommend. Short cranks, relaxed seat tube angles, small wheels and short front centre distances.
The knowledge has been around a LONG time. In modern times the knowledge has been deliberately forgotten.
Anthony