Surly Ogre / Troll Rear Disc Adapter The Surly Ogre and Troll frames take a specific disc adapter. This is the one you need for running a 160mm rotor with a 74mm post mount caliper on the rear of your rig. Features Rear brake adaptor specifically designed ONLY for the Surly Troll and Ogre For use with 160mm rotor only Brake caliper must be 74mm post mount compatible | Surly | Ogre / Troll Rear Disc Adapter 160Mm Adapter