crank length on coker

I have 152's on mine. I didn't choose them, they came that way. I
can't imagine going shorter w/o brakes. I almost come off now going
down hills. The same hill I just make it up. I am sure as I increase
my proficiancy, I will be able to handle the hills a little better. I
have to say that one the flat it is the most incredible feeling. The
wheel starts turning, seemingly w/o effort... almost pulling your legs
along. The ride is sooooo smooth. I am unicyclist.com's newest Coker
convert.😄

--
bugman - Survivor 2004 Wolfman Duathalon
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I've been using 140 mm (5.5 inch) cranks on my Coker. That length seems
to be a good compromise between having good power and torque for going
uphill, slow speed control, and speed on the flats.

I may try 125 mm (5 inch) cranks. But for now, I'm liking the 140's.
The 140's let me go fast enough. Any faster and I'd be cruising at
faster than my run-out speed, and I'm not to anxious to cross that line
yet. The 140's do well for me in hilly Seattle. I do have a brake that
makes it much easier to maintain control on downhills. What's the fun
if you can't make it down a hill that you just went up?

How big are the hills that you plan on riding? You're in Colorado so
your hills can get pretty big. If you're thinking of climbing a
mountain pass then crank choices are going to change.

--
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At this stage in your Cokering career, it is too early to be thinking
about changing the standard cranks.

With me riding, the standard set up with 150 mm cranks is good for
speeds of up to 16 mph, and average speeds of between 10 mph and 13 mph,
and it's good for some fairly tough cross country riding, up and down
hill.

With me riding, two years ago, it was good for tottering about the car
park and falling off the back every now and then.

125s increase the cruising speed but, in my case, made no difference to
the top speed. Nerve (or stupidity!) is what dictates your top speed on
a Coker. Some people put 110s on, or even shorter. Others put 170s on
because they ride lots of steep hills.

Get some miles in on the standard set up. One day, you will *know*
whether you need to make changes.

--
Mikefule - Roland Hope School of Unicycling

Some days you're the fly; some days you're the windscreen. When you're
the fly, you get to eat [censored].
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I am using 150s on mine. They work really well on hills...I can climb
almost anything I can climb on my muni. I'm finding, however, that as I
get more experience on the 36", they're becoming a bit limiting for
overall riding. I'm going to be purchasing a pair of 140s soon, with a
goal of rotating them with the 150s depending on the ride. My favorite
current Coker ride is 23 miles of 2% downhill. The 150s are not
efficient for this ride. Plus, I want to see how many of my local hills
I'll still be able to climb with the shorter cranks.

My 150s are silver. I will probably buy my 140s in black, just so I
don't have to mount up to remember which set I'm using.

John Childs is also urging me to get the 140s, as this will eliminate my
last remaining excuse for why he is faster than me.

--
tomblackwood - Registered Nurtz

Tailgate at your own risk.....

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I've never really understood this 140/150 thing. The difference is only
around 7%. In terms of speed, that's worth about a mile an hour at the
top, and rather less on the cruising speed. On the other hand, the
extra 10 mm on the 150s will be worth a bit more than that (maybe 10% or
so) in terms of torque on a steep hill when the contact patch of the
tyre is "uphill" of the hub.

I guess it's mainly down to comfort. Find a size that suits and ride
accordingly.

--
Mikefule - Roland Hope School of Unicycling

Yoooooooneeeeeeemaaaaaaaaan rides again.
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150mm is a good length to start with- alot is dependent on your riding
style and fitness but if you're starting out then 150 will give you a
reasonable amount of leverage for almost all road riding. Anything
shorter can feel very scary at first, but once you've gotten used to the
Coker- I think 125mm are much more comfortable to ride on the road. It
seems to spin really nice. 125mm works fine on hills too- it's
surprising what you can crank up if you stand on your pedals. And it's
not that scary going downhill either- there is much less choppy leg
movement because of the small pedalling circle. In fact- if I'm going
really fast downhill the 150mm scares me silly- feels like my legs are
flying everywhere.

So now for me:
150mm for most off-road Cokering. Maybe 170mm if it is really
steep/technical
125mm for road including hills
110mm for flat road- I'm still working on this with my TT Coker

--
GizmoDuck - Adventure unicyclist

o-kO

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Mikefule said:

*I've never really understood this 140/150 thing. The difference is
only around 7%. In terms of speed, that's worth about a mile an hour
at the top, and rather less on the cruising speed. On the other hand,
the extra 10 mm on the 150s will be worth a bit more than that (maybe
10% or so) in terms of torque on a steep hill when the contact patch
of the tyre is "uphill" of the hub.*

I'm not sure what the contact patch has to do with torque. Applied
torque is proportional to force on the crank perpendicular to the crank.
It has nothing to do with the rider's balance or forces on the wheel
due to the hill. Since torque is F*d, increasing d by 7.1% will result
in a torque increase of 7.1%. You may be implying, Mike, that longer
cranks also allow one to increase F, or force on the crank perpendicular
to the crank. This would have to be something along the lines of better
ability to put one's body weight on the pedal due strictly to the longer
cranks. In my opinion, it would take some more details to justify a
combined (F,d) increase in applied torque of 10%.

Quoted message said:

*I guess it's mainly down to comfort. Find a size that suits and ride
accordingly. *

This is the best answer, it seems to me, since there are other factors
such as one's leg dimensions and geometry, pedal/foot match, handle
configuration, and even personal weight distribution that affect
hill-climbing effectiveness.

--
U-Turn - Member of Generation XO

Weep in the dojo... laugh on the battlefield.

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'Strongest Coker Wheel in the World'
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Mikefule said:

*I've never really understood this 140/150 thing. *

It's a comfort thing for me. It feels better to spin with the 140's
than the 150's.

I do notice the difference between the 140's and 150's on some hills.
The difference is only really noticeable on tricky climbs where it's
necessary to do a switchback style turn or some other turning maneuver
during the climb. With the 140's I'll sometimes stall out and won't be
able to get the pedals going again after trying to turn. With the 150's
I'll be able to recover and get the pedals going again. The extra
leverage of the 150's does come in handy sometimes.

I'm going to have to try 125's sometime. But for now I'm happy with the
140's.

I do agree that it is way to premature for dubmuni2004 to be thinking
about changing the crank length from the stock 150's. One should first
get very comfortable with the 150's before thinking about trying
anything shorter. Trying short cranks on a Coker before being
comfortable with the 150's is asking for trouble (and loss of control).

--
john_childs - Guinness Mojo

john_childs (at) hotmail (dot) com
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Back to the torque on hills thing...

Perhaps torque was the wrong word. I'm not an engineer.

However, the pedal and crank act as a lever, but the fulcrum is not
necessarily the hub. Just because the wheel rotates at the hub, it
doesn't make the question of leverage simple.

Put a unicycle against a vertical cliff. Imagine (for the sake of
argument) a tyre with perfect friction, so it will potentially stick to
a vertical cliff.

Now, on a 20 inch wheel with a 5 inch crank, and the crank horizontal,
the centre of the pedal spindle is half way between the hub and the
contact patch between the tyre and the cliff. So, pushing down on the
pedal will NOT help the unicycle to climb up the cliff.

Now put the same unicycle on a perfectly horizontal surface. With the
cranks perfectly horizontal, the pedal spindle is 5 inches to one side
of the contact patch, and downward pressure on the pedal will cause the
wheel to move.

Now find a quarter pipe.

Position the unicycle with the cranks horizontal, and place it carefully
at various heights on the concave slope of the quarter pipe.

There will be a critical point at which the centre of the pedal spindle
is exactly above the contact patch between the tyre and the slope.

If the slope gets any steeper, then the pedal is on the wrong side of
the contact patch, and downward pressure on the pedal will not cause the
uni to rise.

If the slope gets shallower, then the centre of the pedal spindle is
"uphill" of the contact patch, and downward pressure WILLcause the pedal
to go down, and the rest of the unicycle to rise.

I recognise it isn't quite this simple, becase there are a number of
other factors, like momentum, a continuous circular pedaling action, and
whether or not you pull up on the seat. However, the basic principle
seems sound: as you are grunting up a hill, you stomp down on the pedals
in the hope that the pedals will go down, and the leverage will act
through the contact patch to cause the uni and rider to rise.

So, imagine a situation where the pedal on a 140mm crank is exactly 10
mm "uphill" of the contact patch. Now swap to 150 mm cranks... the
pedal is now 20 mm "uphill" which will give approximately twice as much
hill climbing ability, call it torque, grunt or whatever.

Now, I accept this is a very simplified explanation, and that the maths
will not be simple, because the pedal is only in this position for a
tiny part of the pedaling circle, and for a dozen other reasons, but it
seems clear to me that as the slope gets steeper, the extra length of a
longer crank makes more difference than it would on the flat. This is
because we are not simply looking at the "magnification" of the movement
of the rim, compared to the pedal, but we are also looking at whether
the pedal is moving down relative to the hill, or the unicycle, or both.

--
Mikefule - Roland Hope School of Unicycling

Yoooooooneeeeeeemaaaaaaaaan rides again.
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This diagram might explain, if I can work out how to post it:

+----------------------------------------------------------------+
| Attachment filename: hillclimb.bmp |
|Download attachment: http://www.unicyclist.com/attachment/211912|
+----------------------------------------------------------------+

--
Mikefule - Roland Hope School of Unicycling

Yoooooooneeeeeeemaaaaaaaaan rides again.
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Hmmm well not to push this thread "over the edge" like so many have gone
before....

Imagine you are sitting on a seat behind the unicycle wheel, with a
counterbalancing weight in front. Just by pedaling you could still go
up the hill, even though your feet are completely behind the contact
patch.

Your point of view is difficult to work with. This in physics is called
"reference frame". It is easier to find insight in some reference
frames than in others. Many times the skill lies in finding the right
way to look at things. For example, in rectangular coordinates, a
circle is hard to describe; in circular, easy (r=4.5, say).

Here let's split the notions. First, the only thing pushing the wheel
forward along the ground is pressure along the surface of the ground.
The only way to do this is to apply pressure on the pedal perpendicular
to the crank (torque). Any pressure parallel to the crank doesn't help.

Second, the only way the rider is going to stay on the unicycle is for
the center of balance of the unicycle to be vertically ahead of the
contact patch, otherwise when he applies torque the wheel will move
ahead of him and he will fall off (oh, the memories).

By examining these concepts carefully, we can see that, if we had a way
to apply torque without shifting our weight forward, all we have to do
is keep the balance point of the uni slightly ahead of the contact
patch, so that we move forward. Assume that we have infinite friction at
the ground so the wheel won't slip.

However, when the hill gets steep we don't have enough strength in our
legs to apply enough torque, unless we shift our weight forward to put
all our weight on the pedal. This is actually more than we need, but
because we can't do that at all positions of the pedals we need to
invest a little bit in the momentum of the wheel to get through the
vertical pedal position.

However, if we had, say, a motor on the unicycle that could apply torque
uniformly around the circle, we wouldn't have to do that, and could
actually creep up the hill as easily as riding slowly on a flat smooth
surface.

So although a longer crank would help us move our weight a little
farther out ahead of the contact patch, that's not the real issue, and
the contact patch explanation is a little misleading. The real issue is
that shorter cranks make the strength/weight limitations on the _torque_
(F*d) more severe, not that they make it harder to reach ahead of the
contact patch.

To see this, think of our motor-driven uni with perfect 360 degree
torque. With shorter cranks, the motor would have to push harder, but
our balancing act, just barely ahead of the contact patch, would be
exactly the same. With longer cranks, the motor would not have to push
as hard, but our balancing act is unchanged.

< I'm ignoring the diagram because it may just make the explanation more
complex. To make the diagram useful would take more elements and
vectors. >

I hope that helps, but it may not be clear enough.

--
U-Turn - Member of Generation XO

Weep in the dojo... laugh on the battlefield.

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I see what you mean, and, yes, I'd forgotten to allow for the fact that
the rider shifts his/her mass away from the centre of the uni. However,
I do think that at the absolute limit, when it's a choice between moving
and not moving, the rider can only meaningfully apply force on the pedal
vertically by putting his/her weight on it, perhaps augmented by a
certain amount of pulling on the handle. In this situation, I'm still
not convinced my theory is wrong.

Perhaps it's my riding style. When I'm stomping up a steep hill, I tend
to put all my weight on the up hill pedal, rather than sitting own and
pedalling smoothly.

In fact, the effect I'm describing may be most noticeable on descents -
but again, my riding style relies on keeping control, rather than
spinning out in a mad dash for glory. So I find myself using all of my
weight to keep the pedal from rising. Now, where is my Centre of Mass
relative to the contact patch? If it's downhill of the CP, then I'm
either going to have to accelerate, or I'm going to swallow dive. If
it's up hill of the CP, I'm going to have to decelerate, or fall on my
back. So if I'm plodding down a hill, step by step, I guess my centre
of Mass is almost exactly over the contact patch, and I have only my
weight on the pedal, and a small amount of down force via the handle to
stop that wheel from running away. And *that* is where I think my
argument has some validity.

But you're right, I hadn't looked athe whole reference frame. That was
partly deliverate (see all the caveats in my description) and partly
laziness.

And IMHO there's nothing wrong with a thread wandering off the initial
subject, as long as it remains legal, decent, relevant and
interesting.
😉

--
Mikefule - Roland Hope School of Unicycling

Yoooooooneeeeeeemaaaaaaaaan rides again.
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I would go along with what appears to be a rough consensus by Coker
experts here, start with the stock 150s. If you're not used to the
larger, heavier wheel, this length gives you enough to work with, and
feel comfortable riding the beast. Then, depending on the terrain you
take it on, you can go up or down from there.

I use 125s for riding to work, with very little in the way of hills. It
works pretty good. A smaller pedaling circle might be nice, but I don't
think I want to give up any more leverage.

I tried 150s for trails, but I thought they were way too short. This is
highly dependent on how much up & down your trails have, and how much
you like to grunt & groan on the uphills. With 170s I was much more
comfortable, except of course on the flats. But I had to admit a Coker
with 170s was quite a bit of fun on a trail as long as it wasn't going
uphill!

Mikefule said:

*125s increase the cruising speed but, in my case, made no difference
to the top speed.*

I think cruising speed is what matters the most. I haven't messed with
top speed on my Coker much. I don't need to find out how fast I can
survive a crash. I'll get enough of that with a 29" in the coming weeks
:eek:

When you lay the cranks side by side, 10mm hardly looks like anything.
But if it's 8 miles to work and 8 miles back, small changes in the size
of circle your feet have to make are very noticeable!

--
johnfoss - Walkin' on the edge

John Foss, the Uni-Cyclone
"jfoss" at "unicycling.com"
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"We choose to go to the Moon in this decade and do the other things, not
because they are easy, but because they are hard." -- John F. Kennedy,
1961
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