My rear pads are down to 3mm and my front have plenty of material left. I bought TRD pads during the 40%off sale for front a rear but since I only need to replace rear pads, is there any problem running different pads front and rear? Also, I will probably put better rotors on the rear. I am going to get front spacer installed along with new shocks so maybe better to just replace the front pads and rotors at the same time.