To find out if tires need to be balanced, conduct a visual inspection. When tires are out of balance, one side of the tire will be worn and the other side will have far less wear. Typically, the side with wear will have flat spots every couple of inches. In addition, tires that are out of balance often make a car vibrate, especially at high speeds.
Before taking a car to the mechanic to get the tires balanced, check to see if another problem is causing the tires to be out of balance. First, make sure the tires are correctly inflated. Tires that are under- or over-inflated have heavy wear patterns on the tread. In addition, under-inflated tires cause a car to vibrate at high speeds.
It is also possible that the front end of the car is out of alignment, which affects the performance of the front tires. To diagnose this problem, pay attention to whether the car pulls to one side. It is best to have an alignment done at the same time the tires are balanced, since changing the tires even slightly can alter the alignment of the car.
Ultimately, a tire that has been out of balance for some time may need to be replaced. Generally, if the tread of a tire is less than 1/16 of an inch, it poses a safety risk.