There are several signs that you may need new tires which include bulges or blisters that could, eventually, lead to tire failure. Other signs may include cuts or cracks on the sidewalls. Making sure you have the proper tire tread is crucial to your driving experience and safety. The tread helps your tires maintain contact with the road and navigate in road conditions such as rain, snow, ice and slush. See here for Your Guide to Buying Tires.