i don't see why you can't use the rear disc brakes , anyway the rear won't be greater then the front , if you had purchase the correct brake set . make sure the rear brake caliper piston is smaller then the front , then u`ll be fine with it . logically speaking , front has shorter travel distance then the rear , cause the fluids need to travel to pressure the caliper pistons , so the front brakes will have great response then the rear due to the short brake line , and when doing hard braking , the front will always lock first rather then the rear . if your rear locks and the front doesn't then its not a good sign , cause you`ll fish tail and lose control under hard braking .