The unicycle rolls on a narrow strip of tyre. Even on a fat tyre, the
contact patch is only a couple of centimetres wide on flat ground.
The pedals are some distance to each side of this contact patch.
The Q factor is this distance.
Why does it matter?
Because the weight of the crank, pedal and foot (and leg) adds up to
quite a lot, and the pedal is "orbiting" the axle. "Centrifugal force"
(yes, I know, but we all know what it means) means that the pedal is
constantly pulling away from the axle. The heavier the pedal and the
faster the rpm, the more it pulls.
So, the further out from the contact patch the pedal is, the longer the
lever (the axle) it is pulling on, so the more it affects the
steering.
Think about this: if the right pedal is pulling the right hand end of
the axle one way, then the left pedal is paulling the left hand end of
the axle in exactly the opposite direction.
For a simple demonstration of the effect, hold your uni up by the seat,
then spin the wheel hard with your other hand. The uni will wobble
jerkily from side to side in time with the rotation of the wheel.
If (for the sake of demonstration) you removed the cranks and pedals
and repeated the experiment, the uni would NOT wobble jerkily from side
to side.
Now, if you increase the Q factor, the degree of jerky wobbling will
increase. if you reduce the Q factor, the degree of jerky wobbling
will increase.
When you are riding, you may not notice the effect except at very high
speeds, but nevertheless it is there, and you are using energy to
compensate for it.
On the other hand, a high Q factor is good for steering, especially
with a large wheel.
Like everything in unicycling, it's a compromise.
--
Mikefule
"...some of the basic stuff, like not killing each other, should be
relatively obvious to anyone."
John Foss, the unicycling philosopher, goes right to the point.
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