Question 353821
Mass is directly related to volume.
Volume of a cylinder {{{V1 = pi*r^2*h}}} where h is the thickness
V2 = V1/2
{{{V2 = pi*r^2*h/2}}}
{{{r = sqrt(V/(2pi*h))}}}
--> the radius decreasing by a factor of sqrt(2) reduces the volume and mass by 1/2.
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This solution is simplistic because it ignores the hole in the wheel used to mount it.  That can be calculated too, but I doubt it's expected.