Manufacturers and many state laws recommend replacing tires when tread depth wears down to 1/16". (When new, tread depth is 2/5" to \\302\\275".) When you reach 1/16" you can see the wear bars (rubber strips which are darker than the tire). If you cannot see the wear bars, insert a penny into the tread, Lincoln's head first. If the tread does not reach the top of Abe's head, consider replacing the tires.