If the rust is flaking, you need to take the tire off and use a drill with a wire brush and brush the flakes off.
If it is just a thin layer (or coloring), you can go to Home Depo and get a small bottle of "CLR" and rub it on the rust. let this sit for about 10 minutes, then wash it off. This bottle should be over in the plumbing section.
If it is just a thin layer (or coloring), you can go to Home Depo and get a small bottle of "CLR" and rub it on the rust. let this sit for about 10 minutes, then wash it off. This bottle should be over in the plumbing section.