inspect tire tread depth

https://aged-wiki.win/index.php/How_to_Test_Brake_Lights_Safely_and_Diagnose_Common_Issues

To inspect tire tread depth, grab a penny and stick it into the groove head-first, with Lincoln's head pointing down. If you can see the top of his hair, it's time for new tires. Also look for uneven wear or low spots, which can indicate alignment issues or underinflation. This quick check helps keep you safe on the road.