Crankarm - 170mm vs 172.5mm

[nscrbug]

Ok...as some of you may know, I am in the process of shopping for a new bike. I am selling my Cervelo Carbon Soloist (51cm) and in the interim, I am currently back to riding my old Trek 2100 WSD (54cm). Problem is...the Trek is a triple, and I don't like it. I stumbled upon a used 105 double crankset with BB and attached pedals (Shimano 105's SPD-SL) for a really good price. The only thing holding me back is...the crankarm length is 172.5mm...whereas on both my Cervelo and Trek bikes, the crankarm length is 170mm. If I were to go ahead and swap out the 170mm triple for the 172.5mm double...will I notice a huge difference??? I really hate to pass up the opportunity to swap my triple for a double at a really cheap price. Yes, I know I would also need to swap out the front derailleur too...and I'm already searching eBay for a used one. If I could make this swap happen for under $100, I'd be a happy camper. But that crankarm discrepancy has me a bit concerned. Would appreciate any feedback. Thanks!

Linda

[arielmoon]

I have had a discussion with several people about crank length and the answers are so varied. One lbs mechanic insists the difference between a 172.5 and 170 is minimal while my bike friend with tons of racing experience says it is a pretty big difference.


My 54" Trek came with a 172.5 while the 56" does as well. When I was having knee issues (that probably are more quadriceps) I wanted to try the shorter crank but I never did. One reason I am hesitant is I feel like I am going to loose the torch I get from the longer crank. Right now its not broke so I am trying not to fix it! LOL

So... to sum up... I think it could be different for you, especially going up and not going down in size.

Btw I have a triple and I have no complaints whatsoever!

[maillotpois]

You will probably notice more of a difference in the change from triple to double (is it compact or standard?) than the crank arm length. I have one bike with 170 (my old bike) and the rest have been 172.5. I really don't notice much of a difference between the two in terms of how they fit.

[TsPoet]

2.5 mm is less than 0.1 inches.
I've gone from 170mm to 155 mm cranks, when I went from 170 to 165, I could tell no difference.
Unless you have knee issues, I doubt you'll be able to tell any difference at all.
The other changes you are thinking of will make much more of an impact.

[OakLeaf]

I think it depends on your legs. Is there any way you can test ride a bike with 172.5mm cranks to see how it feels?

I can ride 165, but if I'm on 167.5, I have to compromise on seat height to avoid knee issues (and wind up with calf issues instead).

[Pedal Wench]

My BF and I just bought new cranks and with the arms laying side by side, it was hard to eyeball the difference between my 170 and his 175. I think different thicknesses of socks might have more of an effect than crankarm length!