I'm a big fan of OPC, especially on tires like Bunky stated. OPC has been the only APC that I have tried to date. When washing my vehicles, I spritz each tire to be worked with OPC full strength, and within 10-20 seconds a brown residue is already flowing to the ground. Hit it with a tire brush, rinse, and all clean. I've found OPC to be rather expensive per gallon, as compared to other products, but so far it has worked really well, and I will continue to use it.