The tires are designed nowadays to do 50-60,000 miles. But when they get down to those wear bars, you don't have as much tread," Allen said. "And I recommend right when it gets down to those bars, you replace your tires." Other factors that you should be on the lookout for are weather cracking and sidewall integrity.

It may be tentative, but tires do have an expiration date. There is a general consensus that most tires should be inspected, if not replaced, at about six years and should be absolutely be swapped out after 10 years, regardless of how much tread they have left.

If your tires are more than 6 years old then you should change them. The second method in determining if you should replace your tires is the tread depth. The recognized smallest safe tread depth is 2/32 inches. You ought to change your tires if it has worn down to that measurement.