Cranks: 172.5mm or 175mm?



CycleFast

New Member
Nov 12, 2005
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I'm 178cm tall with an 86.2cm inseam. I've been riding with 172.5mm cranks up until now. My cadence i usually 70-105rpm.

I sometimes feel that I don't have enough strength (I know... I've read all the strength/weight threads, and I buy all of that ;) ) when I'm riding hard while sitting. If I stand up (using identical power) I feel that I have much more "snap" in my legs and I feel stronger. When I sit I feel I'm lacking the "snap" and I have to struggle more to keep the intensity up.

So... I've been wondering if maybe 175mm cranks could help me get down my perceived exertion (for the same power) while sitting and working on high intensity, since I get more momentum when pushing on the pedals.

Is this a good idea?
Would 175mm fit someone with my inseam length?
Anything else I haven't thought of?

Thanks!

_________
CycleFast
 
Oh, I and just wanted to add that the reason this question ended up this forum (and not the Cycling Equipment forum) is that it's not 175mm cranks per se I'm interested in, it's the "training effects" (consequenses for force requirements, cadencde, etc) I'm interested in.

_________
CycleFast
 
I don't think that extra 2.5mm of torque arm (1.4% increase) is going to give you the "snap" you're looking for. Have you tried using a slightly lower gear?
 
frenchyge said:
I don't think that extra 2.5mm of torque arm (1.4% increase) is going to give you the "snap" you're looking for. Have you tried using a slightly lower gear?
I switched from 175's to 172.5's a few days after getting my road bike. I was used to riding 170's on my mountain bike and I found that 5mm difference quite uncomfortable. It seemed like my knee was coming up too high at the top of the pedal stroke and I was losing power. I guess it all depends on how you've developed over time. Oh, and by the way, I'm 190cm. I guess I should be riding 185's or something.:rolleyes:
 
I think you just have to test them out. There's really no simple way to know if you 'should' have them on your bike. Give 'em a shot. If they don't work, they don't work. :)
 
CycleFast said:
I'm 178cm tall with an 86.2cm inseam. I've been riding with 172.5mm cranks up until now. My cadence i usually 70-105rpm.

I sometimes feel that I don't have enough strength (I know... I've read all the strength/weight threads, and I buy all of that ;) ) when I'm riding hard while sitting. If I stand up (using identical power) I feel that I have much more "snap" in my legs and I feel stronger. When I sit I feel I'm lacking the "snap" and I have to struggle more to keep the intensity up.

So... I've been wondering if maybe 175mm cranks could help me get down my perceived exertion (for the same power) while sitting and working on high intensity, since I get more momentum when pushing on the pedals.

Is this a good idea?
Would 175mm fit someone with my inseam length?
Anything else I haven't thought of?

Thanks!
_________
CycleFast
i believe crank length has something to do with the femur bone length i cant remember why, i am 1cm shorter than you but my inseam is only 80 so you have longer legs
 
I'm 185 cm (6'2") and ride 170's. I used to ride 180's and have had everything in between. All I know is that my ability to spin up quickly or accelerate with snap, has dramatically increased since I lowered my saddle drastically and got 170's. Not sure the crank length had too much to do with it, but I like the idea of shorter cranks for higher rpms and cornering clearance.
 
grom said:
i believe crank length has something to do with the femur bone length i cant remember why, i am 1cm shorter than you but my inseam is only 80 so you have longer legs
Pant inseam or floor to crutch?