I was rereading this article about bike fitting.

https://www.peterwhitecycles.com/fitting.htm

Under the Crank Length section, he talks about using a formula, which involves taking 18.5% of a measured length.

According to that measurement, I'm suppose to be using 162-163mm cranks. Is this right? At 5' 7" with a 30" pant inseam (32" cycling inseam), I think I've got pretty normal proportions.

My current cranks are 172.5mm.

I have two sets of cranks, 170mm and 175mm.

The shorter ones are probably lighter than yours, and the longer ones are just longer.

Either way, mine are better. HA HA.

I have the same as you--5' 7", 30" pant inseam. I've switched--about three months now--back to a crank that has a length of 165mm and it seems to feel pretty good to me. The crank is a Shimano FC-R700 that I acquired years ago, but stopped using for a while.

I've had my eye on a few online sites and it seems like hardly anyone carries anything shorter than 170s these days. I have a new crank coming--the shortest they had was 170mm.

5'6" 32.5" cycling inseam.
I currently have 172.5 on the road bike, 170 on one MTB and 175 on the other MTB.

I love 172.5 on the road. There are a couple of hills in my neighborhood I would dread having 165s for, 170s aren't bad though.

I really dislike these kinds of things where you put in dimensions and it spits out what you "should" be riding. That might give you a good starting point for something like frame size, but to me the rest is up to how you feel.

It would be interesting to see what would trump what between the leverage of 5-7mm more crank length vs. gearing that allows one to spin a shorter crank faster.

+1

In my own unscientific tests riding up a short 30 degree slope on my MTBs, I've still yet to conquer it on 170s even though I never felt like I was running out of gear necessarily. It's a piece of cake to crawl up it on 175s, however.

Maybe someday I'll get some 165 road cranks and do some testing on steep asphalt with those and my current 172.5s. 39x28 on the short cranks, 39x25 on the long cranks.

He even states that there is no magical number for everyone. Cadence preference, femur/calf ratio, etc. all influence it as well. I have long femurs and short calves, but I like to spin, so I stick with 170mm and seem to be happy with them. My mountain bike has 175, which is fine because I don't spin as much.

Please tell me you mean 30 percent. I wouldn't be able to ride up a 30 degree slope with any cranks!

Take a ruler and measure 2.5mm. I doubt that I could tell the difference between 170mm and 172.5mm cranks.

exceptions arise when the person is small and just outside the range of 172.5mm, but 170mm could work depending on preference.
I just don't see a 5'4 person using 170mm cranks, yet that's what many of the bikes in that size are equipped with.

Although you might be correct, I can also believe that someone might be sensitive to such a difference, considering I have a firm preference in trumpet mouthpieces where the differences are far smaller than 1mm.

Crank length is probably one of the least predictable fit options made by measurement. Go with feel every time.

Is it that fine a line between music and fart noises?

Only PCAD knows the difference.

That has me at about 185mm. On one bike I ride 165s and the other I use 175s. I don't like how high my legs come up with the 175s, I'm sure I'd hate anything longer. I don't want cycling to feel like leg pressing

arbitrary pseudoscience

I dont care about scientific measurement... if I am comfortable riding that's all that matters to me. An extra 1%-2% wont matter much if I ever ride in a large group

Wouldn't the difference in pedal stroke be 5mm? Since the crank length is the radius of the pedal circle.

Although I know you meant it as a joke, you could say that. When the wrong mouthpiece might kill my endurance, I would most definitely be making farting noises near the end of a 2+ hour gig!

Pretty sure I'm not... 172.5 and I'm 5'4", but I don't have the money to experiment and don't feel like it's a huge problem or anything. When it's time to replace parts from wear, I'll probably go with 170.

I am about exactly the same body size as the OP. I have 2 bikes that I ride regularly (i.e. each about 2-3 times per week--Bike 1 when it rains, Bike 2 when it doesn't).

Bike 1 has 172.5mm cranks because that's what came with it. Bike 2 was a custom build so I thought, what the hell, I'll give the crank proportional theory a shot and so it has 165mm cranks.

I "think" I prefer the way the 165mm cranks feel, but that bike is newer and fits me better in other ways, so who knows if I'm being completely objective. What is noticeable is my ability to pedal through corners without clipping a pedal so much.

Bottom line is that even a 7.25mm difference is almost imperceptible. FWIW, I'm also a high cadence spinner. Also FWIW, Cavendish rides 170's.

correct

172.5mm i was hitting my chest while pedaling in the drops. 170mm and im fine.