Frames with IS tabs require an adapter for any modern hydraulic brake caliper. The International Standard mount positions two threaded holes 51mm apart, perpendicular to the wheel, while post mount calipers expect parallel mounting holes spaced 74mm apart. The Shimano SM-MA-R160P/S bridges these incompatible interfaces, giving you a platform to bolt your post mount caliper to an IS-equipped frame while positioning it correctly for a 160mm rotor at the rear wheel.

The adapter bolts to the IS tabs using the two included fasteners, creating a post mount surface that faces the wheel. Your caliper then attaches to this surface using its own mounting hardware. The geometry is specific to rear applications with 160mm rotors. Using this adapter on a front fork IS mount would position the caliper for a 180mm rotor instead, since front and rear IS mounts sit at different distances from the rotor centerline. Shimano labels their adapters by intended position and rotor size, so matching the R160 designation to your rear brake setup keeps everything aligned.

IS mounts were the dominant standard on mountain bikes through the early 2000s and still appear on many steel frames, some titanium frames, and budget-oriented hardtails. If your frame has those perpendicular tabs with smooth holes rather than parallel threaded posts, this is the adapter category you need. The construction is machined aluminum, stiff enough to maintain caliper alignment under braking loads without flexing or allowing the caliper to shift position.... Read More