This helpful article that All Tech Automotive wanted to share with you comes from How Stuff Works Auto.
5 Warning Signs You Need New Tires
Just as your feet are sore after a long walk, the tires on your car take a beating every time you drive. This isn't a sign of bad driving --well, not usually -- but rather an inevitable fact of life. Tires get old and worn down. And because a tire failure while you're driving can be catastrophic, causing your car to go out of control or leaving you stranded in the middle of nowhere without any easy way to get home, you want to know when your tires are in bad shape so you can get new ones before something goes wrong. Of course, if you have a mechanic look at your car periodically, he or she will probably tell you if the tires need to be changed, but there are several things you can do yourself short of a visit to your local auto center to make sure your tires are in good shape.
1. Tread Depth
The tread on your tires should never fall below 1/16 of an inch (1.6 millimeters) in depth. If you regularly drive on slick, wet surfaces, you'd be even better off with twice that much. You can buy a gauge to measure the tread depth the way the professionals do, but there's an old trick that will give you a rough idea of how much tread depth you have left and it won't cost you more than a penny.
In fact, it requires a penny. Take a Lincoln-head penny, the kind you find in your change every day, and insert Abe's head (head-down) into the tread. If Lincoln's entire head remains visible, you don't have enough tread. Take your car into the mechanic and ask about getting a new set of tires.
2. The Tread Wear Indicator Bar
Newer tires have a convenience that older tires lacked. They have tread wear indicator bars built into the tires themselves. These bars, invisible or barely visible when the tires are new, gradually begin to appear as the tread wears down. They appear as flat rubber bars running perpendicular to the direction of the tread itself. If more than one or two of these are visible on a tire, the tread is getting low. This should be particularly obvious in the wet tracks that your tires leave after you drive through a puddle. Use the penny test described on the previous page to double check the depth, but if the bars are starting to appear on any or all of your tires, it's once again time to check with your mechanic or local tire dealer to see about getting your current tires replaced.
3. Cracks in the Sidewall
Not all problems with the tires are going to be in the tread. They can also appear in the sidewall. Fortunately, it's easy to do a visual check of sidewall problems. Look for tracks or cuts in the sidewall -- grooves that are distinct enough to be visible to the naked eye. This could be a sign that your tire is developing a leak (or worse, that it's nearly ready to blow out). This is definitely something you want to avoid. So if the cracks in the sidewall are starting to look serious, get that car to a repair shop at the next opportunity and start talking about getting them replaced. Better safe than sorry, as they say.
4. Bulges and Blisters on the Tire
Sometimes the outer surface of the tire begins to weaken. The result can be a bulge or blister that extends outward from the rest of the surface. This is similar to an aneurysm in one of your blood vessels and you know that if your doctor tells you that you have an aneurysm, you'd better get to the hospital as quickly as you can before you blow out an artery. It's the same with your tire. This weak spot can cause a sudden blow out, and if you don't put the car in the hospital (or service center, as the case may be) before this happens, it may end up putting you in the hospital when the tire blows out on the freeway. So keep your eye on those tire bulges and blisters.
5. Too Much Vibration
A certain amount of vibration is inevitable when driving, especially on poorly paved roads, but if you've been driving for a while, you probably know how much vibration feels right and how much means that something's going wrong. There can be any of a number of causes for the vibration -- maybe your tires are misaligned or unbalanced, or your shock absorbers are starting to go. But it could also indicate that there's some sort of internal problem in the tire itself. Even if the tire isn't the root cause of the vibration, the vibration could damage the tire and pretty soon you'll have a problem. So if your car has a bad case of the shimmy-shimmy shakes, especially if you notice this when you aren't driving on bad roads, take it to the mechanic right away to have it checked out. Too much vibration is almost always a sign that something is wrong.
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