Jerry Moos wrote:
>Still doesn't seem to make any sense why they
>used a smaller thread on the hub, unless with
>the smaller pitch, they couldn't get down to the
>smallest desired cog without the OD becoming too
>small.
Bingo!
F'rinstance, a 13 tooth sprocket would have a circumference of about 130 mm, measuring around the centerlines of the sprocket rollers.
Divide 130 mm by ΒΌ, gives a diameter of 41.4 mm, 1.63 inches. Subtract 1.37 standard hub diameter, leaves .36 diameter difference, .18 radius difference.
That .18" would be the distance from the _center_of_the_roller_ to the thread. Need to use awfully small chain rollers to make that fit!
With a standard track sprocket hub, 1/2" (12.7 mm) pitch, you can just barely do a 12 tooth sprocket.
Sheldon "Do The Math" Brown
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