The Penny Test for Tires
If you're starting to notice some wear on your tires, but aren't sure you have more or less than 1/16th of an inch of tread yet (the minimum legal limit for tread depth), the penny test for tires can help you decide just what to do.
Performing the Tire Penny Test
To perform the penny test on your tires, hold a penny vertically, with President Lincoln facing you, then place the coin (head down, but facing you) into several tread grooves in various places on the tire. If part of the President's head is always hidden by the tread, you have more than 2/32" of tread depth remaining.
To further check your tread, you can repeat the penny test, this time with the Lincoln Memorial placed upside down and facing you. Insert the coin into several areas of tread and check to see if the top of the Lincoln Memorial is completely hidden. If so, it means you have more than 3/32" of tread depth remaining.
If you don't have a penny handy, don't despair – you can perform a similar test with a quarter. To perform the quarter test, hold the coin head down, facing you – then insert President Washington's head into several areas of the tread. If part of Washington's head is always hidden, then you have more than 4/32” of tread depth remaining.
What the Information Means
Once you've established an approximate tread depth on all of your tires, you may find that you need a new set. However, if your overall tread depth is in the safe range, perform the tire penny test again – but this time on only the inner and outer grooves. This will tell you whether your tires are wearing evenly. If they're not, a professional alignment or wheel rebalancing service may be necessary.