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Old April 24th 18, 03:19 PM posted to rec.bicycles.tech
Frank Krygowski[_2_]
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Default washer with a little hook in rear fork tracks

On Monday, April 23, 2018 at 9:24:43 PM UTC-4, Emanuel Berg wrote:
Frank Krygowski wrote:

Internally geared hubs exert torque on the
bike frame or dropouts in certain gears.
If the axle has flat surfaces and the
washer's inner hole has matching flats,
I think the washers you describe are a way
the hub transmits that torque to the frame.


Okay...?


To further explain the torque:

With a derailleur hub or a single speed hub, the torque applied to the wheel
by the chain and sprocket is the same value as the torque applied by the
tire's friction force acting on the tire+wheel radius. Of course, the dirctions
are opposite. We engineers would say the sum of the torques must be zero, at
least for constant velocity situations.

When you shift an internal gear hub to a lower gear, the gear hub applies more
torque to the wheel than is applied by the chain and sprocket. That must be
generated by a reaction torque from the dropouts (or on some hubs, from a
reaction arm attached to a chainstay, etc.).


The surfaces are flat! But there is also the
hook! Perhaps the hook is just a way of putting
it (the washer) there so the flats align
easily? But somehow that sounds unlikely!

And what happens with the torque if there is an
ordinary washer?


I think there may be no problems with an ordinary washer, provided the nuts
holding the axle in place are tight enough. In that case, the torque will be
transmitted to and from the dropouts by the friction forces between the nuts and
dropouts.

With the washer, the axle flats transmit torque between the axle and the washer,
and the washer's tabs transmit torque between the washer and the dropouts,
helping the axle nuts transmit torque.

- Frank Krygowski
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