In order to determine whether your tires are legal or not, you will need to measure the tire depth of the tread, otherwise known as the tire tread depth. To take this measurement you will need either a tread depth gauge or a penny.
Step 1: Locate Wear Indicator
At thirty or sixty degree intervals around the tire you will find small dimples. These are wear indicators and are where you will take your tire depth reading.
Step 2: Place Against Tire
Place the tread depth gauge against the tire with the flat side down. Press down on the barrel causing the tip of the gauge to contact the wear indicator.
Step 3: Take Reading
The first number exposed on the barrel of the tread depth gauge is the actual depth of your tread.
Step 4: Repeat
You should take multiple measurements around the circumference of the tire so you can obtain an average measurement.
Quick Check for Legal Tread
Most states require a minimum tread depth of 2/32 of an inch. The quickest way to determine if your tread is of legal minimum depth is to insert a penny with Lincoln’s head into the tread at the wear indicator. If the hair at the very top of his head is covered, your tread is just inside legal limits. If any portion of the space between Lincoln’s head and the motto is visible, you need to replace the tire.
With the above information, you can now use a tread depth gauge and a penny to measure tire depth. It must be noted, tread depth measurements are taken at the point of the wear indicator for them to be effective.