inspect tire tread depth

https://ace-wiki.win/index.php/Why_You_Should_Regularly_Check_Car_Lights_and_How_to_Do_It_Right

Look for the wear indicator bars molded into the grooves; if the tread is level with them, it's time for new tires. You can also use a penny, placing Lincoln's head into the groove — if the top of his head is visible, the tread is too shallow for safe driving.