Many people are confused as to what the shocks on their vehicle do.The job of the shock is to slow down and damp the movement of the body on the wheel.The real function of shock absorbers are to;1)Prevent bottoming,that is slowing down the compression of the spring and create liting force on the wheel.

2}Prevent the tires from bouncing up and down on bumps and absorb some of the energy.

3)Keep the vehicle from bouncing up and down on the springs before settling down.

Here is a few simply test you can do even if you have no mechanical knowledge about automobiles.The same priciple applys for strut suspension.

1}Push your weight down on the front or rear fender and release .The vehicle should bounce up and settle down.If it continues to bounce the shocks are worn out.

2)Drive over a small bump at speed(@20 mph) and the wheel should lift to it and settle down without a thud.(the thud is the rubber snubber)

3)At 60 mph the vehicle should rise and fall quickly over a dip,then stabilize itself after 2 rebounds.If it does not the vehicle will feel like it is floating and this makes the steering very unstable.

4)On rough roads does your vehicle shake and vibrate after you go a short distance?Well if it does,it is because the oil in the shock is overheating and starting to foam.That problem can be corrected with a nitrogen gas shock.

5)The last is to look at the shock or strut and see if it is leaking oil,if so it has no compression or rebound. 

If your vehicle failed any of these tests either the shocks are worn out are mismatched for your vehicle. Some of the best shocks and struts on the market are Bilsteins,Koni,and KYBs .