View Full Version : crank size and freemounting

August 23rd 03, 01:52 AM
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?

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August 23rd 03, 03:32 AM
ubersquish wrote:
> *i was asking cause i just bought some 102mm cranks and was wondering
> if i should wait to replace my 150's with 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.

iunicycle - Old back, new cricks
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August 23rd 03, 03:58 AM
i just reread my original post. i meant the second 'which is easier...'
to have 'learn' somewhere in it. i feel silly now

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August 23rd 03, 09:20 AM
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

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

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

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)

Mikefule - Roland Hope School of Unicycling

"Our greatest glory is not in never falling, but in rising every time we
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