Crank Length Question

[paczki]

I have 175 and 177.5 cranks on my road bikes -- I'm 6'3" -- but I love riding the 170s on my fixed gear. Is here a reason why I shouldn't ride 170s on my road bikes if I want to spin more?

[Ti Designs]

Yes.


Grrrrrr, now I have to explain, don't I?

OK, here's the deal, your muscles move a pivot through a range of motion. Take your hip for example, the glutes fire and your femur is driven down from the hip. Muscles aren't on/off switches, muscle fibers are recruited along it's length over time. Example: let's say you're doing a bench press, there's no weight on the bar and you're only trying to move the bar 2" up and down. add 25 pounds per side and do the same thing. If you're not looking at the bar I'll bet it went well past the 2" mark. Add 45 pounds per side and you couldn't fire and shut down your muscles fast enough to control the distance to that tolorance. It's a timing issue. With crank lengths, the crank length and femur length are what sets the starting and ending angle of the hip. Long femurs and short cranks could have you wasting a lot of energy pushing in all the wrong directions. This also depends on how quickly your muscles react. I've worked with riders who can't spin smoothly past 120 RPMs, others could go over 200.

The rest of this explaination takes place in person with you on the bike - when is that???

[paczki]

We're waiting for your email, Coach!

[Marcusaurelius]

Well I found short cranks don't offer much advantage over longer cranks when I'm climbing hills or when I feel like hammering on the pedals for a bit. I also found shorter cranks just never quite felt right.