tires tires tires

hey guys i am new here and just starting the scrapping game, i have never hauled a load of scrap myself but my grandpa had done it many times with his truck and trailer, which is the same trailer different truck that i will be using, i was wondering what you guys did about tires, more specifically about getting nails and bits of metal in the tires, this seemed to be a problem with the yard we have around here because my grandpa never put decent or new trailer tires or truck tires on, well we have had the trucks and trailer for a few years now and all of them have brand new tires on them, which means i am concerned about what to do about the tires, my step dad finished up my grandpa'a scrap pile and says the area where you bring copper is spotless but the area you bring iron the ground crunches with every step, what should i do?HELP please