It's not uncommon for people to look at their tires and then try to get one more summer's worth of use out of them. The thought process is that old tires are probably safe on dry summer roads, so why not get the new ones before more dangerous winter driving and save a bit of money as well? Unfortunately, this can be a major mistake. No one wants to end up with a flat tire during a summer road trip. Plus, driving on the interstate during a summer vacation can increase the chances of having a dangerous blowout when your tires are at the end of their life. The following are the signs that you need to get new tires now, instead of trying to make them last just one more summer.
Sign #1: Uneven tread wear
Tread wear, if not too severe, doesn't necessarily mean that it's time to get new tires. Light wear is only a problem if the wear is uneven. Tires with the tread wearing down on only the inner or outer surface can lead to a blowout, as well as make the car harder to handle at higher speeds. If this uneven wear is severe, the only remedy is to get new replacement tires. It's also a good idea to determine the cause of the uneven wear. Most often, the car is out of alignment. In severe cases, you may have a bent or otherwise damaged axle that should be repaired before you have the new tires put on.
Sign #2: Balding
Worn down tread should never be ignored. A common tread test is to insert a US penny in between the tread, head first. If the tread is less than the space from the edge of the penny to Lincoln's head, then it's time to get new tires. If you drive on dirt roads or wet roads a lot, then even this much tread may be too little. Once the tread wears down to between 1/4 and 1/2 inch deep, it's time to get new tires.
Sign #3: Powdery or chalky residue
Sometimes age does a tire in before the tread wears down. This is especially true in hot, dry climates where dry rot can set in. If the outer walls of the tire are cracked or chalky looking, or if they are covered in a powdery residue, then the rubber has begun to break down. Slow leaks may also occur, but in severe cases, the tires will simply blow out. Blowouts aren't just dangerous because you can lose control of the car, but they can also be expensive since a blow out can damage rims, axles, and fenders.
For more help, go to sites like this one.