Originally Posted by PepeM

How thick are bicycle discs?

If we assume that the holes are circular, for the surface area of a drilled disc to be larger than that of a solid disc, the following would need to be true:

surface area of exposed material due to hole > surface area of the material that would be there if there was no hole

2*pi*r*th > 2*pi*r*r

th > r

Is that usually the case? What am I doing wrong?