Use a tread depth gauge and place its probe into the deepest groove
Press the gauge base flat against the tread blocks
Read the measurement on the gauge
Check multiple spots across each tire
Measure the center, inner edge, and outer edge of the tread
Compare all readings for uneven wear
Use a penny test if no gauge is available
Insert a penny into the tread with Lincoln’s head facing down
If the top of Lincoln’s head is visible, the tread is too worn
Repeat on all four tires
Check the tread before long trips and regularly during normal use