Your frame has two unthreaded bolt holes spaced 51mm apart in the same plane as the disc rotor. This is known as International Standard (I.S.) mounting.
The BB7 brake has two bolt holes spaced 74mm apart, not in the same plane as the rotor. This is known as Post Mounting. As is very common, you need an adapter to mount a Post Mount brake on an I.S. mount frame The adapter is also the part that ensures the brake caliper sits at the right height/position for whatever size rotor you are using. Most frames are built to be able to run a 140mm rotor on the rear. This would take an adapter with 0mm offset (ie. no offset needed) In order to line up with a bigger rotor, the brake caliper would need to be spaced further away from the I.S. holes. A 180mm rotor is 40mm bigger 140mm, so the adapter is called a "+40mm" adapter (although the radius difference is only 20mm). Some companies label these as "R180", the R meaning rear, which assumes the frame was built for 140mm. (Front adapters are different, forks are usually built with 160mm rotors in mind, so a F180 would only be +20mm, although some new road forks are built for 140mm). It's safest to use an Avid brand adapter with an avid brake, but most brand mixing usually works out OK. I hope this is a useful amount of information. -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To post to this group, send email to rbw-owners-bunch@googlegroups.com. Visit this group at https://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/d/optout.
