Get a tire tread depth gauge. Talk to the mechanic at your local garage or visit an automotive specialty shop. These gauges are inexpensive and fairly self-explanatory.

Insert the gauge into several different portions of your tread. Measure the outer and inner portions of your tire to ensure that the wear is even.

Read the gauge to determine how deep your tire tread is. Ideally, the tread should be 1/16-inch deep, though a little extra tread never hurt anyone.

Test Tire Tread Depth With a Coin

Raid your change jar for a penny.

Place the penny within the tire's grooves and channels. Insert the penny so that Abraham Lincoln's head faces downward.

Check to see whether you can still see Honest Abe's face. If the tire tread obscures his face, then your tires probably don't need to be replaced. However, if the tires grooves are shallow enough that all of Lincoln's face can still be seen, it may be time for new tires.