Crank length thoughts

Just now I have a Size S frame but i’m using 172.5mm cranks (4iii power meter on crank)… with 52/36T.

Since moving down to an size S from an M, I can see that I need to be a bit conscious of toe overlap…

I’m thinking of swapping to 170mm cranks (and sell off my 172.5 stuff).

Do you think there would be a notable difference in how the gearing would feel if I stuck to 52/36T with the shorter cranks?

No. I’ve moved down to 165’s from 172.5’s on 2 bikes. The 3rd has 172.5’s. While I like and think the 165’s are a better option for me personally once seat hight is adjusted correctly I forget about crank length in a few pedal strokes. 2.5mm is very very small. I’d go shorter but, I realize it’s a personal thing not to mention $$.

4 Likes

Recently listened to Colby Pearce’s podcast and he was saying that when fitting a person and going to shorter crank lengths, at a minimum he moves them down 5mm, if not more.

I recently went from 172.5s down to 165s and definitely noticed a difference…if anything I wish I could’ve down to 160s.

2 Likes

@Landis @cnigro are you both talking about road bikes?

I bought a DIY fitting guide and for my height it has me as 170mm, and also my inseam+GT at 170mm

1 Like

Yes.

1 Like

Apart from the crank length debate, I sort of doubt 2.5mm will make a difference with regards to toe overlap. Might be a lot of money to not solve the problem?

1 Like

I just had a fitting on my tri-bike and the fitter wants me to drop from 172.5 to 170.0 or 165.0 to get a more open hip angle at the top of my pedal stroke.

I am 6ft or 182 CM tall

can’t really comment on the 52/36T with any confidence as I haven’t tried the shorter cranks - however I don’t think you would notice the difference

2 Likes

Probably not. When my 52/36t 172.5mm crank failed before Christmas I borrowed a 50/34 172.5mm for a fortnight before using a 50/34 175mm crank for a month or two before getting a new 52/36 172.5mm and never really noticed anything. I do notice my gravel bike with 165mm cranks is a lot more instantaneously spinny but thats maybe its lower gears. I was offered a replacement 165mm crank for the failed one on my road bike and whilst I was tempted with having a 4iii I stayed on 172.5mm rather than buying a new pm.

1 Like

Yeah it doesn’t seem like a lot… but what else could i do?

(I’ve got 170mm on my indoor smart bike and quite like it)

yes…I actually go even smaller on my TT bike

1 Like

If you’d rather have shorter cranks for hip angle / torque reasons, go for it. But I wouldn’t because of toe overlap. You could just as well buy shoes that are 2.5mm shorter.

(Really I think that toe overlap isn’t a problem in most cases when riding, and if, all you have to do is watch your pedalstroke a bit)

2 Likes

I’ve had several different crank lengths over the years and in a blind taste test, I couldn’t tell the difference. That goes for almost any upgrade I do or have done to my bikes. My bike sensibility is about like my food palette, very unrefined.

5 Likes

Did you find your average cadence went up a bit naturally with shorter cranks?

I went from 170mm->165mm and my average cadence went up +2rpm for Z2 endurance pace.

I have +3000hrs of data recorded on my 170mm’s.
About +1000hrs on my 165mm’s.

When I am riding at threshold or VO2max on flats my rpm is maybe +3~5rpm on the shorter cranks.

I notice zero difference with how the gearing feels between the two crank lengths. It comes down to whether you can turn over the pedals. And any time that becomes a problem you shift to your naturally preferred gear ratio.

Maybe there’s a difference on the limits of your gearing (small ring; big cog), and also when you spin up for a sprint. But for me, now that I’m adapted & fitted to both I can ride them interchangeably.

Keywords are adapted and fitted for them.

That all said, I’m faster on 165mm’s because I’m more aero on flats. Most importantly, I can hold the position. Both of these are measurable.

1 Like

Smaller the better. I went from 175mm down to 165mm and then got rid of the cranks entirely.

My pedals are threaded straight into the BB spindle. Threads didn’t match, but a 4 pound sledge and 18" adjustable wrench fixed that problem. If there’s a will, there’s a way.

3 Likes

Sorry my 5 year old version of myself took over my body and made me type that. :point_up_2:

As others said, 2.5mm won’t make much of a difference. I have bikes with 175mm, 172.5mm, 170mm, and 165mm. I think you really need to nerd out on bike fit in order to take advantage of crank length.

1 Like

If you’re on a small frame, you’d likely be better off with 165mm than 172.5mm, regardless of toe overlap. If you care about aerodynamics and don’t have hip dysplasia, the shorter cranks will be advantageous.

4 Likes

My cadence has definitely drifted up a little bit since going shorter. Like the previous poster mentioned my cadence went up a few rpm’s. I actually just looked at the same outdoor workout done before and after the change. Prior to shortening I did threshold efforts around 88-89 rpm. Afterwards the same efforts were done right around 92, so nothing too dramatically different.

1 Like

Don’t intend to hijack but any of y’all run campagnolo? I want to try 160s but campys cranks stop at 165. Wondering if a 3rd party like rotor is compatible

I notice that my cadence is a lot higher on my indoor (smart) bike on 170mm’s. I do have more gears/resistances, 24 I think, and all perfectly lined up (i.e. no chainrings to swap etc), and I use Garmin vector for power.

My indoor cadence is usually around 100rpm which i’m quite comfortable with, but my outdoor on 172.5mm’s I usually average mid 80’s rpm…(I produce slightly more power indoor I think).

As well as reducing toe overlap I had thought I might also see a bump on rpm on the outdoor bike if I reduced to 170mm… but it’s looking unlikely with what I’m reading ^.

I think i’ll try find a 2nd hand lower spec shimano 167.5mm chainset and give it a whirl… and if i like it I can sell my 172.5mm stuff and replace with it with good 167.5mm stuff. I can always fit my Vectors to the 167.5mm stuff to measure power outdoors.