Human: How do I know when it's time to replace my car's tires? Assistant: 
When you start noticing that your car is making unusual noises or shaking excessively, this could be a sign that the tires are worn out and need to be replaced. You can also check the tread depth of your tires by measuring the distance between the outer edges of each tire. If the treads are too thin, it may be time to get new tires.