Tires have built in tread wear indicators or wear bars that run perpendicular to tire tread. The wear bars are thin strips of rubber spread out every few inches. When the tread level becomes even with the wear bar, it is most likely time to replace the tires. Depending on your driving habits, you may need to replace the tires sooner. Tires may also need to be replaced if they are physically damaged, showing abnormal wear or have unusual bulges or cracks. A Bell Ford Advisor can help determine if new tires are needed.