Struts don’t need to be replaced unless your vehicle is bouncing like it’s on a pogo stick or bottoms out in potholes and over railroad tracks, or unless a mechanic finds that they’re leaking fluid or have been damaged.
In a strut-type suspension, the struts are the “shock absorbers” mounted inside coil springs. They control the amount of bouncing created by bumps, dips and peaks in the road and making a hard or sudden stop. Shock absorber is a misleading term, because the springs actually absorb the road shocks. The struts limit the resulting bouncing caused by the springs compressing and releasing. More correctly, they should be called “dampers.”
When vehicle owners experience a loss in ride quality or handling ability, their first notion might be that they need new struts. Advertising campaigns by strut manufacturers to change them every 50,000 miles or so have helped reinforce that notion. Be aware: Unless your vehicle is experiencing excessive bouncing, as described above, or leans excessively in turns, any ride or handling issues (or unusual noises) could originate from other suspension components. For that reason, it pays to have a qualified mechanic check under your car.
A thorough inspection will determine if struts are the cause. The struts could be leaking or the rubber bushings that act like cartilage protecting a joint might have worn, allowing metal-to-metal contact. On the other hand, the problem could be elsewhere. Bushings and other parts in the suspension, such as tie rods, control arms and sway-bar links, can also wear out and cause loose steering, noise over bumps and more body lean in turns.
The more you carry heavy loads or drive on truly rough roads, the faster the struts will wear, but they often last the life of a vehicle if you don’t abuse them. Don’t automatically ask your mechanic for new struts when you sense a problem; instead, explain what you’re experiencing, and let an expert figure out what you need.