Check out Family Flea Market on Old Seaward on the south side of town. Also on boniface near the glenn there is a junk yard of sorts that sells tires. I can't remember the name though. If you come from the glen and take the boniface exit towards debarr you'll see a tesarro a little shopping center (it's blue) on your right. Take the right hand turn just after the shopping center and follow that raod. It'll end with a gate, on the left you'll see a caged area with messed up cars and racks of hoods and doors. Go into the last building on your left and they have tires in there. I don't know how good the selection is though.
[SIZE="3"][B]Check the air tires, thats where the power is generated.[/B][/SIZE]