Years ago when I was a Cub Master, there was always one den leader, whose den always had winning derby cars. I discovered then that they were rounding the tires, thus less resistance. After giving the secret to the other dens things were somewhat fairer. Best way to tound the tires, that I found, was to put the nail (aixle) thru the wheel and tighten it down in a drill. As it's spinning just hold sandpaper against it rounding it as much as you want.
Ray Gattus Sr.
