Abstract: The invention is an adapter chainring for a multiple speed bicycle comprising a derailleur and a crankset having outer and inner chainrings. The adapter chainring has teeth disposed on its outer periphery for engaging the bicycle chain. The adapter chainring defines a plurality of holes which receive bolts to attach the adapter chainring to the crankset in place of the conventional inner chainring of a two chainring crankset, and to a third, smaller inner chainring which is added to the crankset to convert it to a three chainring crankset having additional, lower gears.