Today I have noticed that when I push the rear brake lever (hydraulic disc brakes) the rotor is a little bit bending , but it wasn't rubbing the caliper . I came to a conclusion that rotor is not centered in the caliper , and I tried to center it . I took the pads out , pushed the pistons , installed the pads back and even if I push the caliper all the way into the frame there is very little space between the inside pad and the rotor , and very big between the outside. How can I solve this problem so that the rotor stands right in the middle of the caliper , I think this will also improve the braking power. I though to put some spacers between the frame and the rear adapter , but I am not sure if it is a good idea or no.