Car tires are typically rated to last anywhere from about 40,000 miles and up. Some performance tires are much lower, while other tires are built for long-lasting wear. Do you need new tires? In addition to checking out the tread wear indicators (TWIs; if the bars between treads are the same height as treads, you definitely need new tires!), the old coin tests also work well.
Most tires start out with between 8/32 and 10/32 of an inch of tire tread depth. To help deal with such small increments of measurement, certain tire tread depth and tire wear indicator tests were developed for the average person to be able to check their tires.
Believe it or not, coins are great tire wear indicator. For example, just about everyone knows the tire tread depth “penny test.” Tires need to be looked over periodically to measure tread depth, and the penny test is fine in a pinch. It is done by holding a penny heads-up, upside-down and sticking it into the deepest part of the tire tread. If the tread comes up to the top of Abe Lincoln’s head, it means the tire still has 2/32” of useable tread, the legal minimum in most states.
There is also a quarter test that shows when the tread is safer (for hyrdroplaning. etc.).
Similar to the “penny test,” the “quarter test” is a tire tread depth test that’s done by holding a quarter upside-down and sticking George Washington’s head into the deepest part of the tire tread depth. If tread covers Washington’s head, this shows that the tire has at least 4/32” of tread left and is still perfectly useable. Performance will not be as good as new tires would be when driving over standing water or in other adverse conditions, but it is not as severely compromised as it could be. In terms of tire wear indicators, if your tires pass the “quarter test,” the tire tread depth should still be relatively safe.
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