How do you check your road bike tires for wear? What is the best way to determine if your tires need to be replaced?
If you're not getting regular punctures due to the thin-ness of the tire or the fabric of the tire is showing/damaged, you can keep the tires on (Sheldon). Unlike a car tire, a tubular tire just requires the tire portion to prevent the tube from getting cut up. And road tires should be smooth since you don't need tread.