Review on 🔩 Enhance Brake Performance with Avid Post Spacer Set Stainless Caliper Mounting Bolts (CPS and Standard) by Aaron Carney

There are several types of 20mm post spacers but this is what you need, especially if you have non-Avid brakes. The reason for this is that they come with sets of convex/concave washers that go on either side of the caliper (inside the concave washer is built into the spacer so you don't need as many parts). They allow you to fine-tune the alignment of the caliper; This will help compensate for misalignment of the struts and align the entire surface of the washer/spacer with the underside of the caliper bracket. The same goes for the top of the caliper, as using an adapter will change the angle of the mounting bolts to the caliper bracket from perpendicular to non-perpendicular. Concave/convex washer kits compensate for this. Without a fully mating surface, the caliper will tend to slip as you tighten the bolt. I used mine to mount a TRP Hy/Rd with a 160mm rotor on a 140mm mount to a road bike. The bike came with a one-piece 20mm adapter, but adjusting it was a headache until I figured out what was going on (and why the stock Avid BB7 was so much easier to align because it's a "CPS" style , which has lower bulges/concave washers).