How do you know if your car tires are worn?

To check if your car tires are worn you want to measure the thread depth on the tires. The thread is the thick part of the rubber made of groves and molding. You want to make sure the thread is still there and there is no splits in the rubber or any metal pieces showing through.
you can tell its worn down by looking at the groves in the tire. if they are very thin then its worn down. if they are a nice deep grove then they are in good shape. hope this helps. :)

Take a penny and stand it on it's head. When you insert the penny into the tire tread if you can see the top of Lincoln's head the tire is worn out and needs replacing. This means the tire is worn below 2/32" and is a dangerous tire that has little grip and is prone to hydroplaning. If you cannot see the top of his head you the tire is still safe.