Join Date: Apr 2011
Location: Baltimore, MD
Bikes: 2010 GT Tachyon 3.0
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Bike fit question: Crank size
So I was contemplating going from 30-42-52 to a 28-38-48 earlier.
My current crank is a 175mm crank.
Now, my seat's a bit higher because of the seat post. I changed it out, and now when I push all the way down I feel like I lose power. At BDC, my leg is just barely not bent; I come 1/2cm or less off the seat straightening it, but just the natural spring in my heel can let me straighten my leg fully without lifting. It's a natural shift; my heel isn't flexing enough for me to notice, much less care, that it's not straight.
That's easy, right? Cut the bottom 2cm off the post (it bottoms out in the seat tube), slide the seat down.
Well, my knees are pretty high at TDC too. It's not a stretch for me, but I think it's sub-optimal. The knee itself is closed at around a 60-70 degree angle, and of course my femur is not parallel to the ground at all. Angled up from hip to knee.
I've seen 170mm and 173mm cranks. Does it really make that much of a difference? I'm thinking I don't want another 175 ... a bit smaller seems better for me. Not sure though. I might have to poke around a bike shop I guess.