Measure multiple locations
Use a dedicated tread-depth gauge across inner, centre and outer grooves on every tire. Record the lowest meaningful measurement and check for uneven wear.
Wear indicators
Raised bars inside major grooves provide a visual wear reference. Seasonal performance and applicable requirements can demand more tread than the final wear limit, so consult current provincial rules and manufacturer guidance.
Uneven wear is diagnostic information
Differences across the tread may relate to inflation, alignment, balance, suspension, rotation or use. Replacing a tire does not correct an underlying mechanical cause.