When good road tires go bad
How can you tell if it is time to replace your road bike tires? Generally, road tires don't have a well-defined tread pattern (like a mountain bike or even a car tire), so it can be a little difficult at first to gauge how much wear your road tires have. It's easy to see when your car tires are bald. What you want to look for on your road bike tires is "squaring off" and a flat section in the middle of the tire. In the picture below, you can see this on the tire on the right.
Why does wear matter on your tire? Well-worn tires are more prone to punctures and flats--there's less rubber to protect the inner tube. And worn tires make it harder for you to maintain speed. You'll also have less control when cornering.
How can I help prevent tire wear? Wear is just going to happen when you start putting miles on your bike, but keeping your tires inflated properly will help slow down the wear and extend the life of your tires.