I am trying to decide whether I need a Coker, or should wait for the
commercial availability of the uni.5 * hub to have an effectively
large, yet physically small wheel. Not having an opportunity to try
any of these options, and also for fun, I have developed the following
When you ride your uni and tend to fall to the front, you step more
heavily on the front pedal to correct the imbalance. “Conventional
thinking” (if such a thing exists here) has it that said action
accelerates the wheel and brings it back under your centre of mass.
(Likewise, if you fall to the rear, you apply more backwards pressure
on the pedals to decelerate the wheel and again bring it back under
If you ride a 20" or smaller unicycle, the forward acceleration or
deceleration of the wheel is indeed the main effect from varying pedal
pressure. However, when riding a larger wheel such as a Coker, the
acceleration/deceleration is more sluggish, and requires that pedal
pressure be sustained for some time to take enough effect. One could
say that the pedal ‘resists’ the downward force. Hence, if you step on
the front pedal when you tend to fall forward, you also upright
yourself (with the hub as pivot point) as if you were standing on
solid ground. This of course is a very natural and easy process, that
most humans learn around the age of 1 y.o. Both effects (pedal
resistance and wheel acceleratation) combine and work in the same
direction - preventing you to fall. I think that this is the basis for
the common assertion that a Coker is so easy to ride (once going).
The fact that the pedal ‘resists’ any downward force is commonly
ascribed to a ‘flywheel effect’ of the Coker, with its heavy tyre/rim
at large distance from the hub. I would however argue, that the same
sluggishness would to a large extent also be present in the
hypothetical case that the rim and tyre of a Coker had no mass at all.
Namely, if you step on the front pedal, friction with the ground
prevents the wheel from instantaneously accelerating. Lest you fall,
the wheel can only accelerate if the whole mass of uni + rider is
accelerated, which on a large wheel is inherently a sluggish process.
The work going into the linear acceleration of the total mass is
considerably larger than the work going into increasing the rotational
velocity of the wheel only, even in the case of a Coker.
Now consider a 24" wheel with a uni.5 hub, and the same length of
cranks as implicitly assumed above. The work going into the linear
acceleration of the total mass is almost the same as in the Coker
case, since the total mass is not that much different. Similarly, the
required pedal force is roughly the same (as 24" x 1.5 = 36"). The
work going into increasing the rotational velocity of the wheel (up to
the same velocity at the circumference) may be somewhat less than in
the Coker case, if the tyre and rim are lighter. (The fact that they
are closer to the hub doesn’t matter since we speak about equal
circumferential velocity. Regardless, as argued previously, this part
of the required work is a small fraction of the total work required.)
Hence, the resistance of the pedal to downward forces should be very
much comparable between the Coker and the 1.5 x 24" case. So the
so-called ‘flywheel effect’ should be the same as well, leading to a
comparable ease of riding, ‘cruise control’ effect or whatever you
want to call it. With a 1.5 x 29" (in stead of 24") the effect would
even surpass that of a Coker.
I realise that additional Coker advantages, such as better rolling
over bumps, or aesthetic effects, are left out of the equation. But
hey, so are the advantages of a uni with a switcheable hub.
I welcome any thoughts on above analysis, or on practical experiences
in this respect re the comparison between Coker and uni.5 or
- A uni.5 hub is an internally geared hub in which the wheel rotates
1.5 revolutions for every full revolution of the cranks. It exists in
the prototype stage.
(Disclaimer: I have never ridden a Coker nor a geared uni. Everything
in this post is from experience riding wheels up to 29", and some
basic physics reasoning.)
Klaas Bil - Newsgroup Addict
Grizzly bear droppings have bells in them and smell like pepper spray. - UniBrier