As the "gear ratio" is a function of the distance from the center of the driven disk, any finite thickness on the driven disk means the inner and outer edges are being driven at different speeds. This causes considerable friction on the bearing surface, wearing it out and giving off significant amounts of heat.
As the "gear ratio" depends on the distance from the center of the driven disk, any finite thickness on the driven disk means the inner and outer edges are being driven at different speeds. This results in substantial friction on the bearing surface, wearing it out and producing considerable heat.