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Crankarm length 175 vs. 172.5 Pros and Cons ?(5 posts)

Crankarm length 175 vs. 172.5 Pros and Cons ?eayste
Aug 14, 2003 9:58 PM
I currently have 172.5mm crankarms on my Road bike and
175mm on my mtn bikes.
Would I be gaining or losing anything by making them the same on both bikes ?
I know I get slightly more leverage with the 175's and a slightly lower gear according to some info I found on
But other than that what am I gaining or losing with each ?
Any comments ?
Thickness of a nickel...OffTheBack
Aug 15, 2003 4:11 AM
Theoretically you get more leverage from the longer crank, but lower cadence since the pedaling circle is bigger (your foot has to travel farther with each rotation). Also theoretically, there might be some "muscle memory" effect that would make it better to have the same length on both bikes. However, in reality, I'm not sure you will really notice either effect. 2.5mm is about the thickness of a nickel and that aint much.
Thickness of a nickel...eayste
Aug 15, 2003 11:30 AM
I was thinking along the same lines last night on my ride home from work.
My Commuter has 175mm .
When I got home I jumped on my Road bike with the 172.5mm.
And even thought the 2.5mm is the length , it is effectivly 5mm small circle to rotate though.
While it isnt much on the leverage side.
that 5mm is alot within the range your knee has to move through the circle.
That motion seems to make a difference that I have noticed that my knees are more achy on my bikes with 175mm crankarms vs my road bike with 172.5 .
So it does seem to make a difference. Even with the 2.5mm.
Thickness of a nickel...M_Currie
Aug 15, 2003 7:55 PM
If your knees notice the difference, you've kind of answered your own question. Different knees have different tolerances. Don't forget that if you alter your seat height by the thickness of that nickel to get your seat-to-pedal distance the same as before, you'll feel both nickels' worth at the top of the stroke. I'd listen to the knees.
My $.02...MShaw
Aug 16, 2003 8:56 PM
...I have a mtn bike with some really old Specialized cranks that are 175mm. I normally ride 170s on my road bikes and 165 on my track bike.

Going from 165 to 170 doesn't feel too strange to me (it does feel like it takes more strength to really hammer the 165s, but they spin a lot faster), but the jump from 170 to 175 is funky. The 175s feel like I'm pedaling my old Biopace rings. Go figure.

I found some 172.5mm XTR cranks for my new mtn bike, so I'll let y'all know how they feel in comparison.