Some modern friction formulations are only effective if they are able to transfer a layer of material to the face of the rotor. If this layer is not even and consistent it can result in a brake “judder” when the brakes are applied. A judder is a change in the brake torque that is felt in the
What the friction material needs to transfer a layer of friction material to the rotor is a surface with the right level RA (Roughness Average). One tool that can accomplish this is the Flex-Hone for Rotors by Brush Research Manufacturing.
The hone has balls made of abrasives that wear away as the tool is used. The tool is designed to be used on a lathe (on-car or bench) with a drill that rotates between 300-600 RPMs. Flex-Hone for rotors sells for about $44 and it has been known to last for more than 200 sets of rotors.