What is the penny test used for?

The penny test is primarily used to check the tread depth of tires, which is important for assessing tire safety and performance. By inserting a penny into the grooves of the tire tread with Lincoln's head facing down, you can see if the tread is deep enough to provide adequate grip on the road. If you can see all of Lincoln's head, it indicates that the tread is worn too thin, and the tires may need to be replaced for safety reasons.

In this context, other choices do not apply to the penny test. For seat belt effectiveness, specific pull tests and inspections are performed to ensure they meet safety standards. Testing windshield wiper functionality involves checking for adequate cleaning performance and any wear or damage to the wiper blades rather than using a penny. Determining engine oil level requires a dipstick and visual inspection rather than a test that involves a penny.