Crank length



R

RichVoice

Guest
I've read so many comments in this forum about what length crank to use
on which type of unicycle. Very informative. . . but also very
confusing!

Since I haven't officially learned how to ride yet, I have no plans on
buying another unicycle, and as far as I can tell, the 152s on my Sun
24" are just fine for me for now. But for future reference (since I'm
pretty sure I'll be interested in a Coker eventually), is there a
general rule of thumb on crank lengths? Like, "get shorter cranks for
trials, longer for distance," or, "get long cranks for more power,
shorter cranks for speed," or, "get cranks that are the same length in
mm as your height in cm," or, well, anything?

I've been a two-wheeled cyclist for many years, but never changed the
lengths of my cranks. Seeing all the comments about crank length makes
me think I should give more thought to them on *all* my wheeled
machines!

Thanks,
Rich


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You don't need to change crank lengths on bicycles because you can
change the gearing. For unicycles, this topic has been covered ad
nauseum for years, so if you want to dig around using the search, you
can find tons of information on this. Even enough to build up general
consensuses on what should work well for the majority of people!
Granted, that's the hard part... :)


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johnfoss wrote:
> You don't need to change crank lengths on bicycles because you can
> change the gearing. For unicycles, this topic has been covered ad
> nauseum for years, so if you want to dig around using the search, you
> can find tons of information on this. Even enough to build up general
> consensuses on what should work well for the majority of people!
> Granted, that's the hard part... :)



i hate the "use the search" reply


ok RichVoice you have it pretty much right, with your cranks for power
= longer, speed = shorter.. etc

id say you dont have to change them if you like them the way they are.

if you wanna have more speed enstead of power(like for a coker) then
get shorter cranks like 140mm or 125mm, if you want more power for
hills then get longer cranks like 165mm or 170mm and up. 152 like on
your sun 24 are pretty much neutral in the crank world. They are on
borderline for speed and power, id say keep with them unless you want
more speed or power.


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musketman wrote:
> i hate the "use the search" reply


should we ignore the wealth of useful info that has accumulated over
the years?


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boo radley

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Right, well, I figured I'd covered why I was posting instead of
searching: I mentioned that I've already read quite a few comments.
But what I've read was more along the lines of what someone uses on
their particular unicycle, rather than why a particular length would be
better for a particular task. Of course, I'm sure there are posts out
there which argue one way or another, so mea culpa for not searching
more, I certainly don't want to ignore information posted previously.

Glad to see you're posting, John, I guess my e-mail got caught in a
spam filter.

Thanks for the general clarification, musketman. If I ever graduate to
a Coker, I'll keep the general rule in mind.

Rich


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The general rule is that shorter cranks let you spin faster and smoother
(your feet inscribe smaller circles), and longer cranks give you more
leverage (important for MUni or climbing/descending very steep hills,
or Coker riding).

In general, I would say that I try to ride with the shortest crank
length at which I can comfortably control the unicycle, given the
equipment and terrain I'm riding on. For road riding on a 24 or 29,
that means 125mm, only because I don't have shorter cranks. For
off-road, 125 is still OK for fire roads that aren't too steep, but 150
is more reasonable in most contexts, and 170 in many. (I'm personally
debating right now between a light 24" MUni with 150mm cranks, and a
heavy 26" MUni with 170mm cranks. I've been riding the XC more often,
if only because walking it up unrideable terrain is a lot less work).


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tholub
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what I've found is that longer cranks are not neccessarily the gateway
to more speed. I can spin about as fast on my 165s as I can on my 110s.
However, the effort required to do so is much less on the 110s. The
'cruising speed' is also higher, I guess. If you think that you might
need more leverage, don't be afraid of long cranks, since they don't
really limit your speed, they moreso limit how long you can keep the
speed up for.

-Dave


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flyer
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There is no single general rule, but there are many rules of thumb.

You have five variables: the diameter of the wheel, the length of the
cranks, the section of the tyre, the skill of the rider, and the
preferred style of riding.

Of these, it is easy to pontificate about the first three, rather than
working on the fourth and developing the fifth!

The benefit of short cranks is that you can spin them faster. Your
feet (and therefore your ankles, shins, knees and thighs) have less
distance to move to complete a revolution of the wheel. That means you
can ride faster, and also more smoothly.

The benefit of longer cranks is that you can apply more toque (turning
force, or "leverage") to the wheel. This is useful on hills -
especially on descents where the extra confidence you get from long
cranks is a real benefit.

However, it is not just a simple matter of choosing a perfect crank
length. The ratio of the length of the crank to the size of the wheel
is also important. Very crudely, a 20 inch wheel with 5 inch cranks
will behave very similarly to a 24 inch wheel with 6 inch cranks.

However, this is only true in "ideal" circumstances on a smooth level
surface such as a gym or hockey court. The big wheel will always be
better on uneven ground and long fast journeys. The small wheel will
always be easier to control in tight manoeuvres.

There is a secondary effect that a large wheel (especially a heavy one)
has a flywheel effect, and will tend to smooth out your pedalling,
meaning you can get away with longer cranks without getting into that
horrible bouncy style that can come with trying to ride too fast on a
smaller wheel.

On the other hand, on a bigger wheel, you "tend" to do faster
straighter riding, so for a lot of the time you can get away with a
shorter crank than you might think. See - conflicting advice already!

Until you can confidently freemount and idle, altering your cranks is
not a brilliant idea. You would be modifying your unicycle to suit an
undeveloped riding style. In turn, this would hamper the development
of your riding style.

As a near beginner, struggling to cope with my 26, I fitted extra-long
cranks. Hey ho, it made it easier for me to freemount, but I later
found I was using a very very poor freemounting technique. Once I
corrected this, I found that not ony could I go back to shorter cranks,
but I preferred them - and they made freemounting easier!

There is a safety element too: a uni at high speed can be difficult to
stop under control with short cranks. A Coker or 28 can take 5 or 10
wheel revolutions or more to stop. Shorten the cranks and this effect
is magnified. It is generally considered a bad thing to fall off the
back of your unicycle at a junction, cracking the back of your head and
firing your unicycle torpedo-like at another vehicle.

Many people fit short cranks to achieve speed, but what is speed? It
could be:
1) Top speed on the flat.
2) Average speed over a ride with obstacles and changes of terrain.
3) Cruising speed on average terrain.

Fit super short cranks and you could find yourself with a high top
speed that you never use, and you have to slow down well in advance of
obstacles, and walk some of the hills, so your average speed over a
journey falls dramatically.

As a very rough rule of thumb: if you want to ride far and fast, choose
the shortest cranks that you can comfortably idle with. Any shorter
would be counter-productive.

As a rough rule of thumb, for MUni, choose the longest cranks you can
comfortably spin for short periods. Sometimes you need high rpm in a
burst, either to get up a short rise, or to spin out on a descent too
steep to ride down under complete control.

Another rough rule of thumb: change crank length about 1 size at a time
- don't go from 150s to 102s just like that. Give the new size time to
"bed in" so that you are comfortable with them. Don't be afraid to
experiment.

Have fun. That's why we do it.


--
Mikefule

"The good life is the life inspired by love and informed by knowledge."

Russell
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RichVoice wrote:
> Right, well, I figured I'd covered why I was posting instead of
> searching: I mentioned that I've already read quite a few comments
> so mea culpa for not searching more


No mea nothing.
Your's is exactly the kind of post that I'd like to see more of.
Someone with a question does a search, finds some info, mulls it over
and then asks an informed question. This is the kind of post that leads
to the ongoing discussion about existing topics that's been mentioned
in the other 'search vs sticky' discussion going on at the moment.

Besides, if you never asked, you might never have heard about the
'Constant' (http://tinyurl.com/bqdqc) 'Footspeed'
(http://tinyurl.com/ctdhc) 'Hypothesis' (http://tinyurl.com/bqdqc)...
(Just for a fun bit of reading.)


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boo radley wrote:
> should we ignore the wealth of useful info that has accumulated over the
> years?



To me it always seems a bit off-putting. "We've answered this question
enough times already. Go find it yourself. Talk to us when you've got
something new to say." It takes a lot more effort on RichVoice's part
to dig through the 317 threads that come up in a search for "crank
length," looking for one that has the information that he wants, than
it does for any of us to just answer his question. Besides, now
whenever someone else dutifully searches for "crank length," THIS
thread will come up in the results, and as long as it's in there, it
might as well contain helpful information instead of just telling the
person to search again for what they were already searching for in the
first place.

Longer cranks for power, shorter cranks for speed, essentially. Most
would probably consider 152s a bit on the long side for a 24" uni,
except maybe for a MUni, which your Sun is most likely not. I'm more
into control than speed myself and I tend to like my cranks a bit
longer than most people do, but even I have only 140s, and that's on my
29. For me 152s are about right on a Coker. It's mostly a matter of
your own preference of course.


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weeble

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To avoid danger of suffocation
keep away from babies
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Wow. Now there's a wealth of information! Thanks for the tips. When
I'm ready to buy my next unicycle, I'll have lots of information to
rely on when it comes to the cranks! Not being a speed demon, I
suspect I'll always prefer longer cranks.

And no, my Sun 24" is not a MUni. Thank god.:)

Rich


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RichVoice

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Just to add my bit to what has already been writen:

Another variable is the rider's length of legs and general height. (I
have very short legs and even the 140 cranks on my onza 24" feel like
my knees are going to hit my chin. With the longer cranks that came on
it, it was almost impossible).

Cathy


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Yet another $.02...

I think that functional leg power of the rider is a biggy when
discussing crank length. I ordered my 29 as my first uni, with 150 mm
cranks. Once I was able to get up on the thing and ride, I felt like I
was dismounting just because I was feeling my legs blow out after 100
yards or less. Sure, I wasn't sitting in the seat, but I decided that I
should try longer cranks until my legs got stronger. New 170's worked
great for me. I still had to learn to put my weight on the seat, but I
was riding instead of walking because my legs were toasted. Once I
started to do many things better while riding, I decided that I was
being held back by the 170's, and I have since gone back to 150's.
Someday I will go to 125's, if for no other reason than to just check
them out. But when I was a newbie with feeble legs, the 170's worked
great for me.

Follow your nose and experiment. One can learn all the lessons in any
order - they all add up in the end.

PS: Gilby, thanks for the encouragement to posters that have done some
searching on the topic of their question. I enjoyed hearing your
thoughts on the matter.


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Icycle

Randy
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