How do I know when my tires need to be replaced?

Tire maintenance typically doesn't make national headlines (or a lot of people's to-do lists, for that matter). But with the 2008 U.S. presidential race in full swing, Obama famously claimed that if Americans properly inflated their tires, the energy savings would equal the energy generated from increased offshore drilling. The McCain camp quickly jumped on the remarks, passing out tire gauges with "Obama's Energy Plan" written on the side.

Of course, both candidates recognized that keeping your tires properly inflated not only increases your car's fuel efficiency but also improves your car's handling, braking ability and ride quality. Yet despite these benefits, more than a quarter of all passenger vehicles on U.S. roads have significantly underinflated tires, illustrating just how little attention our tires receive [source: NHTSA]. Over time that neglect, along with normal wear and tear, can lead to tires unsafe for the road. But before we learn how to decide if your tires should be replaced, let's take a quick look at how your tires work.

Modern radial tires are constructed from multiple layers of materials like polyester, steel and, of course, rubber. These layers are designed to provide the tire with the strength and durability to last tens of thousands of miles, but only if the tires are properly maintained. Your tire's tread is particularly important, since it's the only part of your car in contact with the road. The grooves cut into tire tread are crucial for wet weather traction, channeling water away from the tread and keeping your tires in contact with the road.

You can typically see if your tire's tread or sidewall has suffered damage, but visual checks don't tell the whole story. And since worn-out tires can hurt your car's handling or even explode while you're on the road, keeping your tires in running condition is critical for your safety and the safety of others. Read on to find out how you can tell if your tires need to be rotated, fixed or replaced altogether.

Tread Depth and Other Telling Signs

In some cases, knowing when to replace your tires is straightforward. For instance, your tires have tread wear indicators built into them, (typically marked by the letters "TWI" and a small arrow on the side of the tire). If these indicators become flush with the tire tread, your tire has less than the required one-sixteenth of an inch of tread remaining, and it's time to replace the tire [source: NHTSA].

You can also check your tire's tread depth using a tread-depth gauge or even a penny (or a quarter, see sidebar). When using a penny, place the penny in the tread's grooves with Lincoln's head upside down. If the tread covers part of his head, you still have enough tread to drive safely. Of course, your tread doesn't always wear evenly, particularly if your tires are misaligned, improperly inflated or otherwise out of balance. Accordingly, make sure to test your tread depth in several places, checking for bald patches as you go, and inspect both the center and outer edges of each tire to make sure the tread is wearing evenly.

In addition to checking tread depth, you should also look for cracks or cuts in your tire's sidewall, particularly in older tires that haven't seen a lot of miles. If you notice a bulge in your tire's sidewall, be particularly wary; your tire has likely developed a weak spot and need to be replaced as quickly as possible.

But are there cases where a visual inspection won't tell you if something's wrong with your tires? And what can you do to prevent tire problems from developing in the first place? Read on to find out.

Penny Tread Test Costs a Quarter

Although tires are designed to run with as little as one-sixteenth of an inch of tread, performance testing shows that tires with that level of wear perform substantially worse in wet weather. That means you should consider sliding a quarter rather than a penny into the tire's tread grooves when gauging your tire's tread depth. If your tires pass the test using a quarter, that means they have closer to one-eighth of an inch of tread remaining, giving you better cornering and braking on rainy days [source: Consumer Reports].

Caring for Your Hardworking Tires

In some cases, just paying attention to your car when you drive can clue you in to problems with your tires. For instance, if your car vibrates excessively, your tires might be unbalanced or out of alignment. If you start to feel that your car's handling is unresponsive, check to see if your tires are underinflated. If your car seems particularly bumpy, on the other hand, they might be overinflated. Proper alignment, balancing and inflation can greatly improve your car's handling and extend the life of your tires.

To further extend the mileage you get from your tires, have your tires rotated every 7,000 miles (11,265 kilometers) or so, or consider doing the job yourself if you've got a jack and jack stands. Rotating your tires will ensure that they wear evenly, so you'll get the most out of them before you need to head to the tire store.

Lastly, make sure to avoid potholes and other road debris if you can, since those things can knock your tires out of alignment or damage the tires themselves. Considering that the average cost of a replacement tire has jumped nearly $40 over the past ten years, all the way up to $97.97 per tire, getting more mileage out of your tires makes a lot of sense [source: Welsh].

But what happens when you have a tire with lots of life left on the tread, and you happen to run over a sharp rock or nail on the way home from work? Should you fix the flat yourself, take it into a professional or get it replaced? The answer depends on several factors. If the puncture is located on the tire's sidewall, you're out of luck; you're going to need a new tire. If the puncture is located in the tread of the tire, however, your safest bet is to take the tire into a professional, who will take the tire off the wheel, patch the tire from the inside and plug the hole. This option might be a bit pricier than buying a $5 tire plug kit and doing the job yourself, but the repair will be much stronger. In fact, a study of more than 14,000 scrap tires showed that, while 17 percent of tires had been repaired during their life, only 12.5 percent of those repairs were performed correctly [source: Rubber Manufacturers Association]. Considering all that's riding on your tires, a few extra bucks is a small price to pay for a safe ride.

Keep reading for more links on taking care of your ride.

Lots More Information

Sources

Consumer Reports. "Tires: Big Grippers." Nov. 2007.
Consumer Reports. "Tire Safety." (10/15/2009)http://editorial.autos.msn.com/article.aspx?cp-documentid=435303
Department of Transportation. "Many U.S. Passenger Vehicles Are Driven on Under-inflated Tires, NHTSA Research Survey Shows." August 29, 2001. (10/15/2009)http://www.dot.gov/affairs/nhtsa4601.htm
CarTalk.com. "Car Talk Service Advice: Tire Pressure." 4/29/2005. (10/15/2009)http://www.cartalk.com/content/advice/tirepressure.html
Magliozzi, Tom. & Ray. "Cart Talk: When to plug, patch or just buy new tires." Seattle P-I. July 11, 2003. (10/15/2009)http://www.seattlepi.com/wheels/130186_talk11.html
Marinucci, Carla. "Tire gauge pumping up campaign rhetoric." San Francisco Chronicle. August 5, 2008. (10/15/2009)http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/08/05/MN1S124RIS.DTL
National Highway Traffic Safety Administration (NHTSA). "Tire Safety: Everything Rides On It." (10/15/2009)http://www.nhtsa.dot.gov/cars/rules/TireSafety/ridesonit/brochure.html
Rubber Manufacturers Association. "Tire Industry Study: Chronological Age Alone Does Not Determine When Tires Are Removed From Service." May 23, 2006.http://www.rma.org/newsroom/release.cfm?ID=185
Rubber Manufacturers Association. "Tire Maintenance and Safety." (10/15/2009)https://www.rma.org/tire_safety/tire_maintenance_and_safety/tire_and_auto_safety_facts/
Tire Industry Association. "Passenger Tire Replacement." 2009. (10/15/2009)http://www.tireindustry.org/media/PassengerTireReplacement/Passenger-Tire-Replacement.mov
Welsh, Jonathan. "What's Inflating Your Car's Tires." Oct. 7, 2009. (10/15/2009)http://online.wsj.com/article/SB10001424052748704252004574456981150147524.html