inspect tire tread depth

https://testbrakelightsdigest.alderbrief.com/posts/how-to-test-brake-lights-safely-and-effectively-at-home

To inspect tire tread depth, use a penny—insert it headfirst into the tread; if you can see the top of Lincoln's head, it's time for new tires. Alternatively, look for wear bars: those raised strips across the grooves mean less than 2/32 of an inch remains. Running your hand along the tire can also reveal uneven wear. Stay safe.