I used Plasti-Dip
spray (not the liquid in a can that you dip your tool handles in) two years ago on my Goodyears and it's still holding up fairly well. Check this site for a source.
http://garage-toys.com/pldippepr.html
You do have to use masking tape and newspaper and it takes a while to do a tire.
However, when it dries, the product is flexible and fairly durable.
David