Four weeks into the KWWS Intro to Spinning class, and I’ve learned:
- I really hate single-treadle wheels
- Navajo plying is both amazing and horrible
- some very basic physics
The problem with single-treadle wheels is, well, that they only have one treadle! Kwartzlab friend Kevin was patient enough to explain to me what that really means, in terms of how the wheel moves.
If you remember high school physics, you can skip the rest of this =P
We’ve got a treadle, which is connected to the hub of a wheel by an arm. When you step on the treadle, the arm moves up and down, turning the wheel.
But its actually a little bit more involved than that.
Two things can cause the treadle itself to move: it is either being pushed down by your foot (which in turn pulls the arm down, causing the wheel to move), or pulled up by the connecting arm as the rotation continues (the wheel’s momentum causes it to pull the arm up, which in turn pulls the treadle back up).
With the single-treadle design, you depend upon the former for the first half of the wheel’s rotation, and the latter for the second. This means that the wheel’s inertia needs to be sufficient to coax the wheel through at least half a rotation at your desired speed. If the wheel doesn’t have sufficient inertia, at best your rhythm will feel awkward and your spinning will be uneven. At worst the wheel will actually stall.
With the double-treadle design, you have a treadle pushing the wheel for almost the entire rotation. You only need inertia to carry the wheel past the very top and very bottom of the rotation.
Since the wheel’s weight is all ready fixed, the only control the operator has over the wheel’s inertia is the velocity of the spin (which is driven by the wheel’s acceleration, which is driven by the force with which the treadle is pressed). The single treadle wheel needs considerably more force than the double-treadle wheel. You have to push harder. I think the incline on the single treadle may even be greater.
Using the single-treadle spinning wheel is actually more work.
And that’s why I hate them.
ETA: There was a question of what might happen if the wheel had “too much” inertia. In terms of being able to maintain a comfortable, consistent rhythm on the treadle, you don’t want the wheel to have so much inertia that you don’t need (or are effectively unable) to engage the treadle on the next pass. If the wheel is able to keep spinning without you, then not only are you necessarily no longer in control of that spin, but attempting to smoothly regain control as the velocity drops will be awkward.
Ideally, the treadling is something which you don’t need to actively pay attention to, and so you want a steady rhythm you can fall into.
For wheels without treadles and spindles, on the other hand, the more inertia the better — you want to manually spin the wheel once or twice, and have it keep going as long as possible.