Tires are one of the most important safety features on your car and also have the highest impact on your handling and ride. A nice set of new tires can make your car ride like you are floating on air and handle like a Porsche. New tires also significantly improve your braking performance, which yields significant safety advantages.
Replacing your tires is a procedure that most drivers will have done for them as it requires specialized equipment. Most new tires have a tread depth of 1/3 of an inch and we recommend that you start looking for new tires when you are at a tread depth of 1/8 of an inch. A good way to approximate this is to take a penny and put Lincoln's head into the groove with the lowest tread - if you can see the hair on top of Abe's boxy head, you need to buy new tires.
The rubber in tires breaks down over time even if they are not used - this is why there are often cars with boat and camper trailers pulled over on the side of the road with blown tires. We recommend replacing your tires when your tires are over 5 years old, regardless of wear.
The manufacturing date of your tires can be deduced from the Department of Transportation ("DOT") number on the sidewall of your tires. The DOT number is typically 9 or 10 characters long the last 4 digits tell you the date of manufacture. The first two is the week of production and the last two is the year. For example, if the last four digits of your tire are 3912, the tire was made on the 39th week of 2012.
We recommend replacing all four tires at the same time, especially if you have 4WD or AWD. Rotate your tires regularly to get the most out of them.