I usually use rubber model car tires. I set the cake on a board that
has these tires attched to hold the weight of the cake. I am now out of all my tires. Any suggestions on something else to use.

I have used regular size chocolate covered donuts. I used skewers or small dowels to secure them to the cake and iced the bottom of the truck in black or a dark color so the body didn't have to be raised up. I also used crushed graham crackers to simulate the ground it was driving through. Hope this helps.

I don't know the size of the truck, but what about those donuts that are fancy (I think they're called crullers or something). I use donuts as wheels all the time. If they don't have them in chocolate, you can always cover them in fondant, or dip them in chocolate to make them look like tires. My firetruck cake has donut tires, and it is lifted off the ground. Good luck!

I cover styrofoam in fondant and put a dowel through the center of the tire and the cake board to attach.

Macsmom, Thanks for the suggestion duh! I never even thought of that.
it would hold the weight of the cake. You know sometimes you just can't think.