Try the penny test on your tires. Take a penny and insert it into your tire tread with Lincoln's head facing down. If Lincoln's head is totally exposed, you need new tires. If your tire tread touches the tip of Lincoln's head, you have a 16th of an inch of tread depth, which is the minimum.
More tread is better. Some industry groups now suggest using a quarter for your tire test instead. If the tread comes up to the edge of Washington's head that means you have an 8th of an inch of tread depth.
Also look for the "wear bars" on your tires. These are little pieces of rubber, usually set at a diagonal to the rest of the tread. When your tread is even with these bars, it's time for new tires.
It's best to replace all four tires when any one is bald. But if you absolutely cannot afford to do that, experts say, you should put the new tires on the back of your vehicle to help prevent fishtailing.
Rotating your tires as often as your owner's manual or mechanic recommends will also help preserve your tread. The frequency varies, but many manufacturers recommend tire rotation every 6 thousand miles.
Nicks in the sidewalls of your tires are a hazard, too, because they subtly degrade the strength of this vital part that carries your heavy vehicle. And even missing air caps are not ideal, because they will very slowly let air out and dirt in. Proper tire maintenance can be achieved with a few simple tools. You will need a penny or a quarter as well as a tire pressure gauge, which can be purchased at any vehicle service center, tire retailer or the automotive section of your local warehouse store.
Finally, it's a good idea to scrutinize the tires of any used car you are looking to buy.
"Tires are one of the windows into the car's past," said Chris Basso of Carfax, the vehicle history report company.
For example, if a used car has low mileage but the tires are not the original tires, it's possible the mileage is inaccurate because the odometer has been rolled back.
"The tires are a great way to tell if the seller's being up front and honest," Basso said.
Additionally, many Carfax reports contain service information that reveals whether the car's tires have been properly maintained.