shorter cranks = higher seat?

I’ve been experimenting with different crank lengths on my 24" muni, and have come to believe that I need to change the seat height whenever I change crank lengths. Is this a normal thing? Do you do this? It makes sense (to keep leg extension roughly the same), but it just never occurred to me before.

Here’s the rub: Say you go to shorter cranks and raise your seat proportionately. If you’re not highly skilled, this makes mounting noticeably harder, raises your center of gravity, throws off your balance, and generally makes makes you fall on your face a lot more often.

So… any tips? Or rules of thumb?

You are correct. If you change (for example) from 150mm to 125mm, you will need to raise your seat approx 1 inch to make up for it (to keep your riding rotation the same). Yes, this affects other aspects of riding as well. Takes a little getting used to. This is one thing that has kept me from getting dual-hole cranks – I don’t relish the idea of changing my seat height all the time.

Very true i just put 125mm on my 36er and had the seat post cut down to 130mm when i had 150s on it. Had to raise seatpost about 2cm when i did the change :slight_smile:

Yup. My seat height change is generally slightly greater than the change in crank length. I make graduated markings on my seatposts to make it easier to know how far to raise/lower the seat when changing the cranks.

with short cranks, I don’t compensate all the difference, for exemple I compensate around 20mm from 150 to 125mm cranks in order to get a proper leg angle at maximum force down point

Did the same, marked the seat post with a couple of marks for the different cranks I have.
But I never change during a ride.

Good idea on the seatpost marks :wink:

I recently went from 145mm to 125mm Qu-Ax cranks (on a 29er) and yeah, I had to raise the seatpost up about an inch. At first I was worried I’d notice the difference when mounting, but well, I didn’t :smiley: I noticed the weirdness of having no leverage to control the wheel more.

Fantastic. Thanks for the confirmation and tips everyone. I’ll mark the post to make the transitions easier – that should make sorting out this whole ‘ideal crank length’ a lot easier.

Side note: Having people chime in from countries all over the world still amazes me. What a great time we live in.

Should I do this?

Oh hell, why not.

It was a fun topic of discussion quite some time ago and it centered on the concept of the “Constant Footspeed Hypothesis”.

It’s a fun read, we had some fun minds on this forum in times of yore.