Road bike tires provide traction on wet roads, handle the impact of bumps and potholes, grip the road so you can corner and resist punctures from debris. With all this abuse, road bike tires frequently need replacing. Waiting until the tires are completely worn can be dangerous, leading to falls from poor traction or blowouts. To avoid problems, it's important to know when you need to replace the tires on your road bike and be proactive about replacing those that show signs that they might fail you.
Look out for several flat tires in a short period of time. Getting a flat tire every once in a while is a part of riding a road bike. Getting several flat tires in a week is indicative of a problem with your tires. If you start getting flats every time you ride, it is time to replace your road bike tires.
Compare your tires to new ones. Look at the differences between the tires on your bike and brand new tires of the same type. Large differences in shape, texture or appearance indicate it's time to switch out your tires for new ones.
Check for grooves. New bike tires have deep grooves in them to get traction on pavement. As you wear them down, the grooves in the tires get more shallow. Replace your tires if the grooves are extremely shallow or non-existent.
Look for any visible threads or casing. If you can see any strings or anything under the rubber of the tire, replace the tires immediately. Tires with exposed threads or casing are not suitable for riding.
Take a hard look at the tire shape. As road bike tires wear down, the center flattens out. This wearing pattern gives tires a squared-off look. New tires are round all the way around, but tires that need replacing are flatter on the top and do not have a rounded appearance.
Watch out for common problems with stored bikes. If you haven't ridden your road bike in a while, don't get on it to ride until you thoroughly check your tires. Tires on stored bikes can become hard or cracked from humidity and temperature changes. Other problems to look for on road bike tires that were stored include rotting or fraying of the casing in the tire. Any dark spots or strings indicate you need to replace the tires.