Companies that make shock absorbers used to recommend they be replaced every 50,000 miles, but in most cases that’s unnecessary. Shocks and struts (which are mounted inside coil springs on cars with strut-type suspensions) often last the life of a vehicle. They should be replaced if they develop leaks, become physically damaged, or allow excessive bouncing on wavy surfaces and over railroad tracks. A qualified mechanic should inspect the entire suspension system when those symptoms appear, as other components might be at least partially at fault. New shocks or struts won’t cure all ride and handling issues.