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Crank Lenth ?(12 posts)

Crank Lenth ?Steve A
Dec 28, 2001 5:27 AM
I picked up a new bike for winter training. I noticed it had 170mm cranks and I use 175 mm will there be a problem. I raised the seat to compensate but now all my setting seem off? 5mm is so small of an amount can this make a difference? any input would be good.
re: Crank Length ?CT1 Guy
Dec 28, 2001 6:40 AM
Running a shorter crank over the winter will help you to spin better (like Lance)and smooth out your pedal stroke. Strangely, many bikes now come with increasingly longer cranks - must be a carry over from MTB's - which only places more strain on the knees and is more likely to lead to injury.
re: Crank Length ?Steve A
Dec 28, 2001 7:07 AM
Thanks that may make some sense.
big differencemorrison
Dec 28, 2001 7:36 AM
5 mm is a big change. A lot, though, depends on your size. I am 5'5", with an inseam just under 29 inches. I rotate between 172.5 and 170s, depending on what it is I am trying to accomplish. I notice a big difference between these sizes. (I use 170s for spinning, and the larger sizes if I am working on sprints, intervals, or hard climbs.)

If you are interested in going down in size, see if you can swap out the 170s for 172.5s.

Good luck
big difference?Leg Man
Dec 28, 2001 10:18 AM
I bet if you had a 170mm crank on one side and a 175mm crank on the other (and you didn't know which side was which), you would not be able to tell the difference.
funny story about thisCT1
Dec 28, 2001 10:31 AM
I built my TCR a while back and I just grabbed a new Record crank out of my stash.

About a month later I'm sitting next to by bike and casually noticed that my crank had 172.5 marked on the arms. Holy Cow...... I had mistakenly mounted the "wrong" size on my bike. In the mean time I had mounted another set of new cranks from my same stash on my brothers new bike. Well guess what.... I had put the 170's on his bike.

NEITHER of us had noticed this for over a month!!! Get this.... my brother has and still does maintain that there is "a big difference" between 170's and 172.5's. Go figure!!!

Oh.... I did swap the cranks and now I'm at least 1 MPH faster.... ;)

YMMV
JohnG
funny story about thisDave Hickey
Dec 28, 2001 11:47 AM
I did the same sort of thing but with two different sizes. I had Shimano 600 172.5 and 170 arms. I unknowingly put 172.5 on the drive side and 170 on the left side. It took me a month to notice.
maybe, maybe notgtx
Dec 28, 2001 10:47 AM
when I started riding mtbs more frequently, switching between the 170s on my road bikes and 175 on my mtbs drove me nuts. I also started liking the feel of the longer cranks. I switched my road bikes to 172.5 and am happier.
Interesting pointmorrison
Dec 28, 2001 10:56 AM
and one that I never thought of. I wonder how much of the 'differences' that we notice in changes we make are attributable to the fact that we know we made the changes (and hence believe we feel the results)?

Regardless, I still BELIEVE there is a difference, and I would wager that the shorter a person's legs, the more pronounced that difference would be. Of course, I say this with absolutely no foundation.
big difference?Bernie
Dec 28, 2001 1:23 PM
Oh really? and you've tried this? I think not.
The difference in 170 and 172.5Ian
Dec 28, 2001 7:50 PM
If we put 100 riders on 100 bikes, 50 with 170 and 50 with 172.5 and asked them to identify the crank length, I would bet nearly my entire net worth that only 50 would get the length correct. And 50 would get it right because that is the chance they would have when guessing.

Someone on this board once said, "Stack two credit cards on top of each other, that is 2.5 mm". Once I actually did that, I realized that losing sleep over the 170 vs. 172.5 vs. 175 crank debate was worthless.
maybe for some, but not allTig
Dec 29, 2001 10:02 AM
The more you ride over the years, the more sensitive you are to minute changes in bike fit and positioning. Having ridden 170's for track, 172.5's for road, and 175's for MTB throughout several years, it was quite noticeable when switching between the 3 different bikes that had very similar positions.