question on a 90 amp vs 120 amp alternator

17mm was the same size as my treadmill motor shaft. seems a pretty common size for modern imported alternators and motors. I took the pulley off a Dodge minivan alternator and used it on the 90V DC treadmill motor to reduce the ratio for a bandsaw build. That and a 10.5 inch pulley brought the speed down and the torque up.