Crank Length

Frinton said:

Hello everyone,
I have been riding road for about 4-5 years now. I ride a size small Giant that came with 170mm cranks. I upgraded all of the components on the bike several years ago to Ultegra-Dura-Ace mix. I have covered 25-30k in the last several years. My cycling inseam is about 30 inches. I still run 170mm cranks and want to know your opinions on what cranks you are running proportional to your inseam. I am trying to figure if I should change crank length to a shorter or keep my 170's. It would be great if I could see people that have around my inseam length and what crank size they are running. Maybe helpful also what saddle height as well..........

A 170 mm sound to be about right for you. Your saddle should be adjusted about level and when you sit square on it your heel should reach the the pedal.
This is a good starting point but after that many mile I assume you know whether you are comfortable or not.

I use 180 mm and my inseam is 36.6 in.

Some info on crank lengths, and the UCI Hour Record holders problems regarding crank lengths.

I have found myself most comfortable on 175's. My inseam is about 30 inches.

The point is that the formula doesn't provide one with the only possible answer.

You should see if you can borrow some 172.5 and just see how they feel. I think that would be more beneficial than going shorter.

POGATA said:

I use 180 mm and my inseam is 36.6 in.

Some info on crank lengths, and the UCI Hour Record holders problems regarding crank lengths.

hmmm, interesting about Sosenka. I didn't know he had to fight to use the cranks he wanted. That's an old article; does anyone know what's happened since then?

I've gotta say, I'm not shooting the messenger, but I farkin hate that 21.6% of inseam formula, and I wish it would just blow up or just go away. The guy who came up with it (Kirby Palm) basically just pulled it out of his [censored] to suit his 'theory', then Zinn and a couple fo other guys jumped on it to suit theirs.

He (Palm) reckoned that because a whole bunch of guys in the old days with 31" inseams used 170mm cranks, then that was the 'best' relative length. He found a length he liked, then found some data to suit his idea. There were a million different guys with a zillion different leg lengths in the old days using 170, 172.5 and 175mm cranks, but he just 'decided' that is his 'opinion', a 31" inseam with 170mm cranks was best.

What would the inseam be on a 6ft7 guy like Sosenka? I'm 182cm, and mine is 89.5cm (35.2"😉. I'd still bet his cranks aren't near 21% of his inseam

The 3 main advocates of long cranks on the 'net are all tall guys who were frustrated at the lack of availability of cranks longer than 175mm in the old days when they raced, then they eventually got 180s (and longer), liked them, so they've generalized from their preferences.