The depth of the tread on car tires is important to safety because it is the part of the tire that helps it grip the road. Tread depth is also a signal of the health of a tire. Low amounts of tread depth can indicate the potential for tire failure, hydroplaning or inability to perform in snowy conditions. Tire tread with a depth of less than 2/32-inch is illegal and unsafe. Measuring this depth is not difficult and requires only a few minutes of time.
Use a tire tread depth gauge. This is a simple device with a metal or plastic outer cylinder and a calibrated gauge that slides up and down inside the cylinder. The gauge has a thin probe that sticks out on the other end that is inserted into the tread of the tire.
Push the top of the tire tread gauge until the inner gauge is fully depressed.
Insert the probe on the other end into one of the treads on the tire.
Push down on the outside of the gauge until it touches the edges of the top of the tread.
Lift the tire tread gauge from the tire, and read the lowest number showing above the top of the outer cylinder. Make sure that you are reading on the side of the gauge that measures in 30 seconds of an inch. If so, the lowest number will tell you how much tread remains on the tire at the point where you measured it.
Repeat this process across all treads from side to side on the tire. If possible, also check around the circumference of the tire at intervals of about 1 foot.
Repeat all of the measurements for each tire on the vehicle.
A penny can be used during an emergency to check tire tread depth. If all of Lincoln's head is visible, you need to replace the tire.
To increase safety, consider changing tires that have less than 4/32-inch tread depth.