Wolf Tooth Components Drop-Stop Elliptical Chainring: 38T x Shimano Asymmetric 110 BCD, For Shimano Asymmetric 4-Arm Not compatible with 9 speed chains The simplest way to explain the way these rings feel is having 2 teeth less in the weak part of your pedal stroke and 2 teeth more where you have the most power Features Wolf Tooth's Drop-Stop tooth design for maximum chain retention Optimized for use with 10, 11, and 12 speed chains Ring Position/TYPE: Chain Retaining Single Ring