When checking your tires, which of the following is not something that should cause concern?

When inspecting your tires, be alert to a number of potential problems, including air pressure that is too low or too high; bad wear; cuts; tread separation; dual tires that come into contact with each other or with parts of the vehicle; mismatched tire sizes; radial and bias-ply tires used together; and cut or cracked valve stems. Additionally, verify that there are no regrooved, recapped, or retreaded tires on the front wheels of the bus.