Shock Absorbers and Strut Inserts
![Coil spring and shock absorber in rear coil spring suspension.](graphics/shock-absorber-2.jpg)
Shock absorbers and strut inserts dampen the oscillations and bounce from the suspension coils passing over bumps in the road. Test a shock absorber's ability to return to normal by carefully pressing down on the bumper at the side with the weak shock. Be careful not to damage the bumper.
![Shock absorber function.](graphics/shock-absorber.png)
A good shock absorber quickly comes to rest and returns to normal. A faulty shock or strut continues to bounce. It's because the weak shock absorber allows the coil spring to continue to oscillate.
Cupped Tires
![The Shock Bounce Test](graphics/shock-bounce-test.png)
Bad shocks and struts cause cupped tires. Perform a bounce test on the shocks to see if they oscillate, and test drive the vehicle to see if it floats and leans excessively around corners.
![Tire wear patterns](graphics/tire-wear-patterns.png)
Bad shocks result in cupped tire treads. Tire wear can also indicate a worn steering or suspension component, an over or under-inflated tire, or a misaligned vehicle.