A planetary gear mechanism for a bicycle internal hub transmission that includes at least one stepped planetary gear. The stepped planetary gear has a plurality of first helical gear teeth with a first outer diameter and a plurality of second helical gear teeth with a second outer diameter that is greater than the first outer diameter. The first helical gear teeth have a first helix angle and the second gear teeth have a second helix angle with the first and second helix angles being angled such that for a given amount of rotation of the stepped planetary gear corresponding travel points on the first and second helical gear teeth move the same axial amount with respect to the rotational axis the stepped planetary gear.