My inseam is around 31.5, what crank length would work for me? For those of you who have a similar inseam as me, what crank length do you use?

You're likely splitting hairs over 5mm or so.

All of them.









Seriously though for a fixed gear 165's are the best idea but in the end its personal preference.

165's or 170's

not much of a difference.

I like 172.5 the best, but run 170s. I have 32.5" cycling inseam.

175 on SS MTB.

How long is your femur. Measure it and we can dial you in perfectly.

I have a bigger inseam than you (85cm) and ride 165mm cranks.

Depends on which bike I'm riding - the cranks are 165mm, 170mm (twice), and 175mm. They all feel fine but I wouldn't recommend the 175s for a fixed gear unless you have a really high bottom bracket.

I'd say it's around 14 inches give or take

I'm going to be using a cinelli vigorelli, the bb drop is 58mm. I'm not sure about how high that is with the wheels on (700c x 25c) but if you know that would be a great help!

Cranks come in 2.5mm increments for a reason.

In terms of impact, that's like the difference between a 48x18 and 48x16. "It's only two teeth", right?

Bingo!

It depends on everyone's unique combination of:
- Femur length
- Terrain (hilly vs flat)
- Riding style (spin vs mash)
- Gear choice
- What feels right

Again, cranks come in 2.5mm increments for a reason...just like frames come in 2cm increments for a reason.

About 5

I did the math in another thread long ago, and it came out to be a 3% difference in cadence gained/leverage lost when using 165's over 170's.
48/16 vs 48/18 is something like a 12% gear inch increase, so that's quite a bit more drastic.

Your point comes across, although in this case, it's definitely splitting hairs. I doubt OP could notice the difference between 165's and 170's. I bet very few could actually.

Leverage is one thing, but there is also footspeed.

Footspeed is the speed at which your foot is traveling in a circle. For a given cadence (say 100RPM) the foot must travel faster using longer cranks because the circumference of the pedal stroke is bigger. It will require less torque in the process, but the foot must travel faster.

I'll try to do the math...one sec...

That was the cadence difference I was referring to. Now that I know the term for it, I can better put it in words.

Given a the same footspeed on 170's, and applying it to 165's, it results in a ~3% faster cadence.

165mm
Circumference = 1037mm = 1.037m
Cadence = 100RPM
Time = 1min = 60s
Speed = 100 * 1.037m/60s = 1.728m/s


170mm
Circumference = 1068mm = 1.068m
Cadence = 100RPM
Time = 1min = 60s
Speed = 100 * 1.068m/60s = 1.78m/s

(1.78 - 1.728) / 1.728 * 100 = 3%

So, to keep the same cadence using 170mm cranks that you would using 165mm cranks, you'd have to move your feet 3% faster.


Oh wait...you just did that.

At least we got the same results.

For each 2.5mm increment there is a 1.5% difference in footspeed and mechanical leverage. So if you aren't using 150's or 200's, it's definitely negligible on the street.

Stick to your 165's and 170's op.

I guess my point is that it's not negligible.

It all depends on the factors that I listed above. Given a choice (which the OP has decided to make) those factors should be considered. If needed, it may have to come down to terrain. If it's flat, go 165. If it's hilly, go 170. Still can't decide? Go 165. "Spin to Win".

+1

It has been a few weeks and I still feel weird getting back on 170 cranks. I need some 175s on here. But I dont count.

You're 9 feet tall.

jk, I have 175's on my roadie, and 165's on the kilo.

You forgot the most important two (in my opinion):

- the ground clearance of your bottom bracket
- how much you want to lean over in the corners

I'm used to my motorbike where I can (and do) almost lean 90 degrees before it hits the road, and even then the footpegs just fold up to give you a few more inches of clearance.

If I haven't ridden a bicycle for a while, I almost always strike a peddle to the ground within the first few minutes.

I have a feeling you have no understanding of angles.

I agree that a 5mm difference is big. Finding the best length can only be done through trial and error, though. As far as terrain is concerned, it's basically a wash. Shorter cranks = harder going up, longer cranks = harder going down. 58mm drop is a high BB. Pedal strike shouldn't be an issue.

Get the best of both worlds and go 167.5's