crank size and freemounting

is it easier to freemount with short or long cranks? and if the answer is ‘it depends on what you’re used to’, then which are easier to freemount with?

Longer: you have more control.

That is my .02 cents worth. --chirokid–

I agree with the 'kid. I’ve used different crank lengths on my 24x3 Muni and my 28’er and it is definately easier for me to freemount using the longer cranks. I believe it is because of the added leverage supplied by the longer crank, making it easier to get the wheel rolling from a stop

i was asking cause i just bought some 102mm cranks and was wondering if i should wait to replace my 150’s with them until i got better at freemounting. so it’s easier with longer cranks, but since i won’t be using them (the long ones) after i learn, should i put the 102’s on soon as i get them?

That is a big jump. Maybe try 127’s. If you are worried, practice the rollback mount, and then rollback mount to idle. Rollback is easier than the regular static mount. But I doubt you are going to fail badly based on crank length, it will feel really weird.

actually, static mount is easier for me than rollback. and my 150’s are too long for me to idle with

i just reread my original post. i meant the second ‘which is easier…’ to have ‘learn’ somewhere in it. i feel silly now

I have an easier time mounting on my 20" with 127s than with my 24 with 158s. I guess it’s because I’m short.

I have ridden unicycles with wheel sizes 16, 20, 24, 26, 28 and 36, and with crank sizes 89, 102, 110, 125 / 127, 150 / 152, and 170 mm although not all 48 possible combinations…

There are two things to consider: absolute crank length, and relative crank length.

Absolute crank length: if you have very short cranks, your feet move in a smaller circle. This circle can be divided into sections - for example, the ‘power stroke’ is from around 1 or 2 on the clock face down to around 5 or 6; the position for the pedal during a static freemount is between about 7 or 8 on the clock face and about 9 or 10.

So, if your style of freemount requires the pedal to be between, say, 7 and 9, then those two positions are about 108mm apart on 102s, and 181mm apart on 170s.

Conclusion, the shorter cranks need you to be a little more precise in the setting upof the position of the unicycle before starting to mount. An ‘error’ of a few mm is more significant on shorter cranks than on longer ones.

Now relative crank length. 150mm cranks are about 6 inches long. The radius of a 24 inch wheel is 12 inches. This can be expressed as a crank:wheel radius ratio of 1:2, or 50%.

Put those same 150mm cranks on a Coker, and you produce a ratio of approximately 1:3, or 33%.

What this means is that with the lower number, a small movement of the pedal produces a large movement of the unicycle. That’s why you can go fater with short cranks, or with a larger wheel - within certain limits.

This is all to do with leverage, which means it isn’t just distance and speed which are affected. There is also a difference in ‘torque’. That means that with short cranks, you need more pressure on the pedal to turn the wheel, or that the wheel can exert more ‘back pressure’ on your pedal. So the lower the ratio (as a %) the less fine control you have.

In practice, what this means is that there is a ‘double effect’ if you try to freemount with very short cranks (102 or less on a 24 or smaller; 110 or less on a 26 or bigger - approximate guidelines only).

First, you have to be a bit more precise setting up the position of the unicycle for the mount; second, you have to be much more precise about the amount of pressure you put on the pedal, and when during the mount.

Very short cranks combined with a large wheel can produce at least two freemounting problems:

  1. If you position the wheel badly, a slight push as you launch yourself can allow the pedal to move up slightly and pass the point of no return, and the unicycle scoots forwards away from you.
  2. or you can do a rollback mount, and the uni passes under you and you don’t have enough leverage to stop it and it scoots away behind you.

Conversely, if you use very long cranks, especially on a smallish wheel (say 170s on a 26) then the leverage is so great that if you try a static mount, with the pedal at about 8 on the clock face, it can be difficult to keep your weight off the pedal enough to perevent an unwanted rollback. A tiny mistake with your weight distribution can be magnified by the massive leverage of a long crank and a small wheel.

Now moving back towards the original question:
Freemounting with a static mount is easier than a rollback unless you can idle confidently. A rollback is part of an idle movement.

Freemounting a 20 with 125s, or a 24 with 125s or 150s is probably easiest. 150s on a 26 or bigger.

110s on a 20 are very manageable. 110s on a 28 require a little care.

102s on a 24 require care and practice. Smaller than 102 is starting to get extreme.

Lots of practice enables you to make the transition fairly easily.
The other day I took the following fleet out:

That’s a range of wheel sizes and crank sizes, and some very different ratios. I was able to freemount one after the other and ride them to the car. Adjusting takes a moment, but it’s no big thing.

Useful hint from when I was still learning, and from later when I’ve been teaching: if you’re struggling to freemount a new wheel size, new crank size or a new ‘combination’, then mount against a wall, and ride the uni for a while to get used to the pedal response. Then freemounting will be easier.

So, practise practise practise. ;0)