You need to ensure that your tires have adequate tread and are properly inflated to safely operate your car. Otherwise, you risk danger where the rubber meets the road -- especially if there's a blowout. So if it has been several years since you purchased new tires, perform a simple check to see if it's time to roll them into retirement.
Check to see if any of the tires are bald. If so, replace such tires immediately.
Take a regular penny and place it in between the grooves in the tire's tread.
Determine if you can see the top of Abraham Lincoln's head. If so, you probably need new tires. This is especially true if you drive in adverse weather conditions often, such as rain or snow.
Perform the penny test in several places on the tire. If you see uneven wear, it may be an indication that the car needs to be serviced or aligned.
If any part of Lincoln's head is obscured by the tread, your tires are likely OK. Consult a professional if your tires are borderline based on the penny test. This test is merely a quick way of estimating how much life you have left on your tires.