How often you change your tires depends on a number of factors including what sort of car you own, where and how you drive it, and how well you care for your tires. Responsible drivers should be aware of the basics about tire wear, how to test for wear, and know how to decide when they should change their tires.
Tires are constructed with a pattern of grooves and ridges on their surfaces, which is referred to as tread. Tread increases a car's traction on the road and diverts water from beneath the tire in wet conditions. Although tires are designed to provide reasonably consistent performance throughout their lifetimes, tread does wear down over time and gradually becomes less effective.
The nature of the compound that particular tires are constructed of largely determines whether one tire will wear down more quickly than another. Tires made of softer compounds provide greater responsiveness and braking performance, but they also wear down quicker. Most tires are considered to have a life of between 25,000 and 50,000 miles before they need to be replaced. However, these numbers are only averages. A car owner's manual can include specific recommendations regarding how often and in what manner tires should be replaced for a particular model of car.
How often tires should be changed depends not only on the tires but also on usage. Fast cornering, heavy braking and rough road surfaces can all wear tires down significantly. Poor maintenance and overloading are also detrimental -- the National Highway Traffic Safety Administration (NHTSA) recommends that drivers check tire pressures at least monthly. Tires also degrade even when they are not being used. The NHTSA recommends that tires be replaced every six years regardless of the number of miles driven.
Proper inflation is the Holy Grail of tire maintenance. Too much or too little air in your tires is guaranteed to cause you trouble and uneven or excessive wear over time. Check your owner's manual or the label inside the driver's door for the recommended inflation pressure for your car's tires.
If you are considering buying a used car, it is worth inspecting the tires of the prospective vehicle and asking some questions about their maintenance and general usage. This will allow you to estimate whether you will also need to purchase a new set of tires as well as the vehicle itself.
When assessing your tires, you will definitely need to measure the amount of tread remaining. There are three methods for doing this, and several measurements should be taken on each tire to ensure a reliable assessment of its overall condition. The first method is to look at the tread wear bars, which are little rubber bridges in the grooves between the ridges. If these bars are level with the tread pattern, then the tire has only 1/16th of an inch of tread remaining and must be replaced.
Another test is known as the penny or quarter test, which involves inserting a penny or quarter into the center of the tread between two ridges with the image of Lincoln's or Washington's head facing toward you. If you can see the very top of the head, or worse, the space above the head, then the tire needs replacing immediately. If only some hair is visible, then it is time to consider purchasing new tires, though the need is not so urgent. If some of the forehead is concealed, there is still adequate tread.
The third option for measuring tread is to buy a depth gauge. As these are cheap, easily available at auto parts shops, and simple to use. They are often a worthwhile investment and have the advantage of providing a more accurate measurement than the other methods.
It is also important to inspect the tires for other problems such as cuts or slashes, visible wires, or damage to the sidewall of a tire. Tires may also wear out irregularly, which can decrease the life of a tire and may be related to poor wheel alignment or suspension issues. These should be addressed during car service or at a tire workshop. Tire rotation may be helpful but is not feasible for all models of car, many of which use wider rear tires.
The type of tire you use will give you a part of the answer to the question of how often you should change your tires. However, the way in which you use your vehicle and care for your tires can alter their longevity significantly. It is worth familiarizing yourself with the section of your vehicle's manual that addresses tire selection and care as well as ensuring that you inspect your vehicle's tires at frequent intervals to judge whether it's time to replace them.