While all four rims were off getting new tires I took a look at the brake pads and rotors. The two front rotors were bright and and the pads looked flat. The two rear rotors were dirty and the pads were concave against the rotor. The guy at the tire shop said this was normal for dodge trucks. Looks like to me that rear brake don't even work if the rotors are dirty. What would make the pads concave shaped? is this normal?