Right now I ride a speed concept with 172.5mm cranks. Primarily training for 70.3 and IM distances. Could someone give me the advantages and disadvantages of switching to smaller cranks, say 165mm? I’m 5’9, 155lbs if that matters.
The primary advantage to shorter cranks is that they allow you to lower your cockpit while still keeping your hip angle relatively open. There is not really any reason to switch from what you have currently unless you are having problems or are wanting to go lower in the front.
Right now I ride a speed concept with 172.5mm cranks. Primarily training for 70.3 and IM distances. Could someone give me the advantages and disadvantages of switching to smaller cranks, say 165mm? I’m 5’9, 155lbs if that matters.
As mentioned before, it’ll open up your hips so you can get a bit more aero.
But… smaller cranks lead to higher effective pedal motion ratios. All your gears willl feel “taller” by the ratio 172.5/165. A 39-25 will feel like a 39-24. If you need your largest rear sprocket, then consider swapping more teeth in at the rear.
will smaller cranks give me more power at the top (12 o’clock) position of my stroke? since my knee won’t be as bent, therefore a better muscle length-tension relationship?
They won’t just give you any “free” power, but if your hip angle is currently pinched closed at the top of your stroke, they will open that up and allow you to have a more complete and smooth pedal stroke through the top.
will smaller cranks give me more power at the top (12 o’clock) position of my stroke? since my knee won’t be as bent, therefore a better muscle length-tension relationship?
You develop power not your bike, your bike converts it to forward motion.
A shorter crank will not increase your perception of the power you are putting down are will reduce the torque you are applying (for the same pedal force) think about using a long V’s short tire iron to remove a wheel nut.
Just coz it worked for Crowie, doesn’t mean we all need to do it… 
what I have noticed after about 1 month on a 165 from 172.5 is a smoother pedal stroke.
what I have noticed after about 1 month on a 165 from 172.5 is a smoother pedal stroke.
Which one is smoother?
It’s all about who you know
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what size cranks does Crowie use?
any other pro’s of medium stature riding less than 170’s?
what size cranks does Crowie use?
What others use, be they Pro or otherwise for this discussion is almost completely irrelevant. I know this is hard for people to get their heads around. This like several, other things when it comes to bikes and bike fitting is HIGHLY individual.
Changing crank length should only be considered if you are having “problems” with your current set-up. Consider this, while going shorter seems to be in vogue right now, some will go shorter and be “worse” for it!!
The 165’s.
I’ve switched from 170’s to 165’s for about 5 weeks now and I really don’t notice any difference. I’m going to swich back to see if I can tell any difference.
jaretj
To:… A 39-25 will feel like a 39-24
You are saying you are losing power, will have to “fee” like your pedaling harder…Disagree.
This id the same argument I have had with a guy who on the road wanted a longer crank because it would be easier to pedal, generate more power…No…Pro roadies would be riding 180’s+
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why did you switch? What were you hoping it would change?
I noticed a change in my pedal stroke that appeared this year. I started noticing it in races, then noticed it happening in training as well and it was only on my TT bike; I didn’t have that problem in the past and it doesn’t happen on my road bike. I put on Q rings, that helped little but still had some slop that I wanted to try to fix, the shorter cranks seem to have done that.
To:… A 39-25 will feel like a 39-24
You are saying you are losing power, will have to “fee” like your pedaling harder…Disagree.
This id the same argument I have had with a guy who on the road wanted a longer crank because it would be easier to pedal, generate more power…No…Pro roadies would be riding 180’s+
Ummm… where did I say that he would lose power? Please don’t falsely attribute stuff to me and then compare me to some other guy you had an argument with, ok?
I said that your gears would feel taller. Look:
smaller cranks lead to higher effective pedal motion ratios. All your gears willl feel “taller” by the ratio 172.5/165.
Same torque, same power, but higher pedal force.
If you find that you almost stall on a climb with a 172.5mm cranks, then consider changing the cassette for more teeth when changing to 165mm cranks. That was my message.
Clear enough?
Well we choose to disagree. Cheers …Simce you are saying more pedal force,would not something like a power meter measuring from the pedals measure more power? (vector pedals)
Well we choose to disagree. Cheers
Not sure which part of what I said you’re disagreeing with…
Disagree that smaller cranks lead to higher pedal forces? Disagree that you might have to swap cassettes to preserve motion ratios?
Well you probably missed my edit…But also if stalling on a larger crank thing, I disagree, I do not think the difference would be that great. The opposite would also be true. You could get by with less teeth on the cog by going to bigger cranks…just do not see this as being so. Guys like Obree would of being using 185 cranks for the hour record…So, yes we disagree. I am not flaming, just don’t agree…A pedal measuring system will not read the same power if power, torque is the same but pedal force is different…Seems to me the powere reading would be different if the pedal force is different
Well we choose to disagree. Cheers …Simce you are saying more pedal force,would not something like a power meter measuring from the pedals measure more power? (vector pedals)
No.
Power = Torque x angular velocity.
Torque = L x F, where L is the length of the crank arm.
For the same torque, F needs to be higher. since L is smaller.
Imagine going up a hill at the same speed on a 100mm crank, for example. A lot more force is needed at the pedals to maintain the same climb speed if you don’t change your gearing.
A Vector will need to be configured to know L in order to calculate your power, or will indirectly determine it using an accelerometer.