What kind of tires do you put on your derby cars...The tires that come on the car. Or a heavy ply tire....I have been running 14'' on the back of my cars, and 13'' on the front...

last year we were cleaning up a freind of mines shed becouse they had a tire hual off so he broke out the sawzaw and i brought over the cattle trailer(witch we filled twice and had a few left) but all the tires still on rims we cut off with a sawzaw and i was screwing off with some of the beads and we shoved a bunch of them inside of a flat tire laying around-like a 14 in rim for a dodge car he later ran- but he never put any air in it and it looked like it was aired up other than off the beed but worked great for a rear tire on a fwd car

ive heard of putting feild tile in tires- havent tried it yet, going to easy to find for me grandpa lays it

doubling is hard much less for a 13inch tire becouse you cant find much smaller than that to fit inside without robbing the lawn mower