I just bought an Iverson Grand Sport to take up riding in place of jogging which I did for 41 years and which my back no longer likes. The original 26 x 1-3/8 (no ISO) tires I had changed to Kenda K40's, 26 x 1-3/8, ISO 37-590, and they fit great. I'd post pictures of the bike and some old Iverson ads I found, but this forum has a ridiculous (IMHO) rule that doesn't allow picture posting until one has made 10 posts.