A rotor for a permanent magnet generator includes a rotor body extending between a first end and a second end, having a cylindrical bore and a plurality of flats on an outer peripheral surface. Permanent magnets are positioned at the flats. An outer ring surrounds the permanent magnets and defines an outer diameter. A ratio of the outer diameter to an axial length between the first and second ends is between 3.2 and 3.4. An integrated drive generator and a method are also disclosed.