Shimano Compact cranks get inner chainrings with tooth profiles that specifically address the greater shifting demands imposed by Compact's 16 tooth difference in chainring size. This special profile is designed to prevent the chain from falling off when shifting down to the inner ring. Combined with other Shimano advances in shifting technology, these rings enable the use of a standard front derailleur with compact cranks. Compact specific chainrings mean that you don't need to worry about compact specific front derailleurs!