Join Date: Feb 2008
Bikes: Ventana El Ciclon, Walt Works 29er, Specialized Enduro (fixed up for my son).
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strait cut and paste from Sheldon
A bicycle wheel should have the rim centered directly in line with the frame. The forkends
are symmetrical with respect to the frame, and the hub axle locknuts (or equivalent surfaces) press against the insides of the dropouts.
Wheels should be built so that the rim is centered exactly between the axle ends on the hub. In rear wheels, the spokes attach to flanges
which are not symmetrical about the denterline...the right flange is usually closer to the centerline than the left flange, to make room for the sprocket(s)
When rear wheels are built properly, the spokes on the right side are made tighter than those on the left side, pulling the rim to the right, so that it is centered with respect to the axle (and to the frame.) Viewed edgewise, a rear wheel built this way resembles a dish, or bowl, since the left spokes form a broad cone, while the right spokes are more nearly flat.
By extension, the term "dish" is used as a general synonym for accurate centering, even in the case of symmetrical wheels.
See also my Wheelbuilding article