I'm not sure I have anything intelligent to add to this discussion of physics and bio-mechanics in cycling, other than to say that my cranks are longer than I thought.....and my wife says my cranky moods are longer too...
Seriously, I actually measured the cranks on my 29er, and found them to be about 178, center pedal axle to center spindle. The shop must have put on longer ones than stock, to make them fit me better. I am grateful for that, as it seems I've hit the sweet spot in seat position, bar reach and height, and crank length. Since I made the adjustments last week, the knee pain is all but gone. Pedaling is MUCH smoother and more powerful, stability is better, and most importantly, the stress on the knees is noticeably diminished. I think I will move my shoe cleats back to bring my feet more inward again, but that is all I will do for now. May play around with bar position at some point, but just want to enjoy the riding for a while and not make too many changes at once.
I went on my first single track ride tonight, and the bike just felt great. So stable and smooth, steering was spot on -- agile, yet not squirrely -- and hill climbing was great with the new alignment. It's all good.
LP and JR: as for your discussion of crank length, it seems you are both coming to the same point from a different direction -- it is true that a longer crank creates more turning force (torque) than a shorter one for a given force on the pedal; and conversely, it is also true that a longer crank requires less force on the pedal to create the same amount of torque as a shorter crank. For a taller rider, having a good geometric fit that a longer crank provides seems (logically) to have the added benefit of making pedaling easier. OTOH, does that mean a shorter rider has to work that much harder? Not sure about that one, as, like Jim said, smaller riders weigh less (usually), and the geometry of the bike frame is totally different for the smaller size. Seat tube angles, wheelbase, etc., are different for smaller frames, but I really have no idea what effect that has on pedaling efficiency.
Interesting discussion, and having made some minor tweaks to the alignment of my bike, I am amazed at how much benefit (or loss) can be had from just a few centimeters adjustment. Kinda like skis and boots too......same analogy. A small change can translate into big gains.
Home
Login
Register