A car's shocks and struts have a tremendous impact on its ride and handling. Replacing the shocks and struts is a routine part of maintenance, though it isn't done as often as something like an oil change. There is no set time to replace shocks and struts, and deciding when to replace them is a based on how they feel on the road, as well as how many miles are on them.
The best way to tell if you need new shocks is by simply paying attention to how they feel. Worn shocks can make a car handle very poorly, increase body roll and decrease stability. If your shocks are soft and bounce up and down over bumps and dips, that is a sign they will need to be replaced. One way to test how well the shocks are working is by pressing hard on all four corners of the car near the shocks. If the shocks are in good shape, it should be difficult to get any excess movement from the suspension. Also, when you press down on the corner, the shock should rise back up quickly. If the suspension bounces up and down easily, the shocks are most likely worn.
Generally speaking, a set of shocks can last around 50,000 to 60,000 miles, though this is by no means an absolute figure. Some shocks may last for only 30,000 or 40,000 miles, while others may still be functioning after 100,000 miles. Factors that affect this include how the car is driven and the conditions it is driven in. A car used predominantly for freeway commuting will have less wear on the shocks than one driven in stop-and-go traffic and on potholed surface streets. Likewise, if a car is driven off road frequently or on dirt roads or even rough roads, the shocks will experience more wear.
Another reason you may want to replace your shocks is if you want better performance from your car. As originally equipped, cars and trucks usually have relatively compliant suspensions. By installing a set of high-performance shocks, you will improve the handling and sometimes even the ride quality.
If an older car sits for a long time without being used, the shocks can sometimes freeze up and stop functioning. If you are going to start driving a car regularly that has been sitting unused for many years, you might have to install new shocks.
