Hope e Bike Chainring Black Variant:Brose The inner material and outer Size:S (29") The inner material and outer material of the pump are both made of aluminum wheels identified as 27 It made sense therefore to develop Direct mount chainrings that are specifically designed to withstand the additional rigours of E Bike use Asymmetric tooth profile engineered for cross compatibility and functionality with different drivetrain systemsSpeed Compatibility: 9 10 11 and 12 Speed (including SRAM T Type and Shimano HG+)Mud Shedding: Improved capabilityChain Retention: ImprovedDrivetrain Performance: Optimized for extreme chain angles on modern 1 x drivetrainsDurability: Tooth profile allows more chain wear before function is compromised