I found that using 152mm cranks on my 24" unicycle is causing knee friction with the frame especially on the left. When I changed it back to the original 124mm cranks the knee friction stopped.
It is a feature of my particular anatomy that when I bring my feet next to each other, my knees touch each other slightly (2-3 cm) before my feet do. Could this kind of anatomic characteristic inevitably require me to use shorter cranks? Or could it be a particular characteristic of the way I am riding (I am a beginner) or of my unicycle? Has anyone had similar experiences?
More generally, does the unicycle require one to meet certain anatomic proportions (within a range)? What are your ideas and opinions?
You may want to pay attention to what is called “Q” factor. It has to do with the distance that you would consider the width between the pedals. The 2007 Holm unicycles had pretty wide Q factor, some hubs have cranks that come off the axle at 90 degrees resulting in less Q factor. I find myself to be most comfortable with some Q factor–that would allow you to ride a unicycle with your feet (and hence your knees) farther apart.
Think it might have to do with the fact that your knees go higher with 152s than they do with 124s. Are your knees naturally bent inwards when you walk?
If it’s causing you stress, try correcting your riding gait - you might want to get used to gripping your seat with your thighs less so you can move your knees further apart.
Thanks Carey for explaining this concept of the Q factor. I never knew about it. It sure helps to know about it. Indeed my cranks come off the axle at 90 degrees. Had I known earlier, I would have ordered ones with wide Q factor. I might still order them.
Do your knees touch the frame at the bottom of your stroke? If so, maybe the difference is simply that with 152’s your foot goes down further and therefore the knee gets closer to the crown of your frame. The 125’s would keep your foot higher and your knee wouldn’t touch the frame. Keep your legs straight when pedaling and it shouldn’t happen with either cranks.