If you've got a perfectly good SRAM Rival hydro group with post-mount calipers and you're looking to upgrade to a new frameset with the newer flat-mount standard SRAM's got you covered with the Rival 22/Rival 1 Flat Mount Caliper. Sure adapters exist allowing your flat-mount frameset to play with your older post-mount calipers but have you seen them' It totally defeats the purpose of the sleek flat-mount road specific design and these calipers come with brand new pads too which is something you've probably neglected to change out by now. The big advantage with the flat-mount standard is its simplicity allowing for a sleek design that saves weight. The front caliper requires an adapter that can be oriented for 140 or 160mm rotors and the rear caliper attaches directly to a flat-mount frame's chainstay for 140mm native and a small adapter for 160mm use. This serves to clean up the looks and it offers some claimed aerodynamic benefits. While we haven't verified the claim of less drag it certainly makes sense as the closer the caliper can sit next to the frame and fork the smaller the footprint is to the wind. And now that many aero frames are coming equipped with discs and citing nearly zero aero drag penalties compared to the rim brakes it solidifies this. Other than losing the post-mount tabs the flat-mount caliper is virtually the same as the original calipers. It shares the same pad design bleeding technique and tools and brake fluid. Please note that flat-mount calipers will only work with 140 and 160mm rotors depending on which adapters are used.