Thanks for the web site, great info for anyone with a question on motorcycle tires. I scaned the site (and saved it to my favs), but I still don't think I have an answer to my original question. Why aren't you suppose to put them on a Harley? As to Hobbit's comment on weight, I only used the Wing as an example of a bike weighing as much or more than a Harley and uses radial tires. The two ply sidewalls seem to work for the Wing. Way not for my Road Glide? All the dealer says is it is not reccomended by the manufacturer of my motorcycle.