Troll/Ogre Rear Disc Brake Adapter- Rear brake adaptor specifically designed ONLY for the - Â Â Surly Troll and Ogre- For use with 160mm rotor only- Brake caliper must be 74mm post mount compatible- Brake Caliper Mount: 74mm Post- For Rotor Diameter: Rear 160- Frame/Fork Mount: 51mm IS Rear