When and why a Tire should be Replaced
After working for a major tire corporation for a little over 15 years, I've learned a lot about tires and particularly why and when a tire should be replaced. With the current expense of tires, one wants to get their miles worth out of any given tire but when is it taking it too far? Let us examine further why a tire should be replaced and when it is necessary to do so.
Any tire, whether it be for a car, truck or van is considered to be worn out when it has reached the minimum tread that it can be driven on by law according to the National Department of Transportation. This legal minimum tread depth is currently 3/32's of an inch. To determine if a tire is at this minimum legal tread depth, one can use a device known as a tread depth gauge in one of the grooves between the tread blocks, or one can insert a penny upside down into one of these grooves, If any part of Lincoln's head is obscured by the tread, you're all set - you have a legal and safe amount of tread. However, if you can see above Lincoln's head or any of the "In God We Trust" letters above his head, then you are ready for a new tire. Check your tires in several tread locations. Be sure to check the inner, outer and middle grooves of each tire, because tires can wear differently on each side, due to improper wheel alignment and/or low inflation.
Another reason to replace a tire is if you see a bump in the tread of a tire as this may indicate a broken belt within the tread area. Tires are manufactured with several nylon plies and then steel belts in order to ensure the longevity of the tire In addition a tire may be worn on one of the edges as stated above and one may see the steel belts or even worse, the nylon plies that would normally be beneath the tread surface. These are two other possible conditions that would require tire replacement.
Finally, other reasons to replace a tire would include an irreparable condition, such as a nail or other foreign object too close to the edge of the tire. The general rule is, if a foreign object is lodged within 3/4 of an inch of the edge of the tread, the tire is considered irreparable. The reason being, as a tire curves on the inside a patch won't hold as the tire rotates down the road and plugs are not recognized as a safe repair method. In addition, upon looking at your tires you may see a bulge in the sidewall. This bulge is called an impact break and is produced from the condition where the tire made an impact with a hard surface, and thus caused the belts to overlap in the tread, resulting in a bulge on the sidewall.
In conclusion a tire should be replaced if one of the following conditions apply: the tire is at or below 3/32's of an inch, the tire has a broken belt (represented by a raised section of the tread), one or both edges show the steel belts or nylon plies, a foreign object too close to the sidewall of the tire (3/4's of an inch or less), or if one sees a bulge protruding from the sidewall of the tire.
