DISC BRAKE: POST MOUNT VS. INTERNATIONAL STANDARD

Q. Can you tell me the difference between an International Standard (IS) and Post Mount (PM) standard for disc brakes? I am lost and confused…thanks
A. RC: International standard caliper mounts refer to the flange-style that have threaded eyelets. The mounting screws are oriented from the side of the bike–parallel to the axle. Post-mount caliper bosses are easier to incorporate into fork castings, because the thick stubby towers require less precision to manufacture. The screws are oriented at 90-degrees from the axle. parallel with the rotor. The advantage to the post mount is that the caliper can adjusted laterally to align with the rotor simply by using slotted holes. I.S. mounts require a number of thin shims to make this adjustment. Because most brake calipers are designed for post mounts and require adapters for I.S. type flanges, post mount arrangements are slightly lighter. BUT….The rear caliper mount (because it is usually an extension of the dropout) naturally lends itself to the I.S. flange-type mount. Sooo, most bikes use a mumbo jumbo of adapters–with a post-mount fork and an I.S-mount swingarm.