Even on a short drive, a shock or strut may have a million cycles of up and down motion. Billions and billions of cycles may happen over 80,000 miles. What wears out on a shock or strut is the fluid and gas inside and the seals that keep the ingredients inside. Andrew Markel explores how the fluid and gas can escape and what happens to the stability of the vehicle. Sponsored by Auto Value and Bumper to Bumper.