Tires are designed with treads that provide your vehicle with traction. This traction keeps your car driving along the road - even in inclement weather. Without tread, the elements would literally lift your tires off the road. When you drive through snow or a puddle, the grooves in between the tread blocks of the tires become channels that divert the water or snow away from the tires, allowing the tires to maintain traction in these slick conditions.
When the tread gets worn down, the water, snow, and other slippery substances don’t have anywhere to go except directly under your tires severely decreasing your vehicle’s traction. If your tires are nearly bald, traction will be eliminated completely. Decreased traction will negatively affect your control over the car, making the vehicle unsafe for you and your passengers. Tread depth will determine whether or not you require new tires. You can easily tell if your tires’ tread is too worn by using a penny or a quarter.
The penny test is the gold standard for measuring tire tread-depth because it is easy and it works. Just take a penny and, with Lincoln’s head upside down, put it between the tread blocks of the tire. If you are not able to see the top of Lincoln’s head – if his head is “buried” between the tread blocks – then you still have more than 2/32 of an inch of tread remaining. If you can see the top of Lincoln’s head, it’s time to go tire shopping because the tread is worn down to or beyond 2/32 of an inch.
Flip the penny over so that the Lincoln Memorial (pennies from 2010 and earlier will have the memorial on the back) is facing you and put the penny between the tread blocks with the memorial upside down. If the Lincoln Memorial is completely hidden, you have more than 3/32 of an inch of tread left.
Some automotive experts believe that using a quarter to test tire depth provides a better read than using a penny. Some independent tests have concluded that cars were able to stop faster with tires that had a little more than 4/32 of an inch of tread depth, which is the measurement the quarter test indicates. To perform the quarter test, put a quarter between the tread blocks of a tire (just like the penny test) with Washington’s head upside down, If you cannot see the top of Washington’s head, you have 4/32 of an inch of tread or more.
Whether you go with Lincoln or Washington, both coin tests are also good ways to check to see if your tires are wearing evenly. Simply do the test between other tread blocks and if the measurements aren’t the same on all the tire treads, the tires may need to be rotated or your vehicle may require an alignment. Different types of treadwear will indicate how your tires are wearing. If you don’t have any coins handy, check to see if the tires’ wear bars are showing. Wear bars run across your tires tread pattern from the outside edge to the inside edge. If the wear bar is visible you are in need of new tires as you have hit 2/32” of an inch of tread depth. Most states consider a tire’s service life over if any point of the tread is at 2/32” or less. If you are still unsure, your local Pep Boys can evaluate the depth of your tires.