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Re: [ST] New Member



Colt45 wrote:
> If the rear wheel applies a moment to the SSSA, what resists that
> moment?  Specifically, what keeps the wheel's axle from rotating CCW
> looking from the rear?
>
> If the rear wheel load is 400 pounds and the contact patch centerline
> is 4" to the right of the center of the SSSA (essentially at the chain
> line), what keeps the 1600 in-lbs from rotating the whole swing arm
> CCW?

I don't think the wheel is applying a moment to the SSSA. The spindle/rear
axle is rigid (as is the swinging arm itself) and the centre of the point of
support is directly in front of the contact patch of the tyre. As long as
the member transferring the forces is rigid it shouldn't matter what it does
(in terms of shape) between the point of application of the force and the
point of support (other than internal loads/stresses).

You can demonstrate this to yourself by bending a paper clip into a shape
with a U sort of thing 1/2 way along (basically so it looks like a highly
simplified SSSA diagram) and apply a force at one end and hold the other.
There is no twisting. But as soon as you press on the outside edge of the U
(the force is now off center to the point of support and there is an overall
torque) it twists in your fingers. I suck at ascii art but I've attempted a
diagram of what I'm talking about with the paper clip below (viewed from on
top).


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Phil
'02 S3


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