Disclosed is an adjustable ring shim for a planetary traction drive designed for a driven turbocharger on an engine. The adjustable ring shim has two parts that interface through a ramp feature to provide an ability to vary the overall width of the ring roller assembly of the planetary traction drive. This adjustability in the width of the ring roller allows for setting a desired preload force on the traction surfaces of the traction drive during assembly, even with variation in manufacturing of the different parts of the traction drive.