Shock or riser pads are rectangular polyurethane pads which can be installed between the deck and the baseplate. The baseplate is the lower part of the trucks, which is connected to the deck by a mounting kit. Basically, shock or riser pads have two simple functions. First, they increase the distance between your wheels and the deck, thus reducing the risk of wheelbites. A wheelbite is an abrupt contact of the wheel with your deck, which results in an unintended and often unexpected stop. So if you ride very large wheels or very soft bushings, it is recommended to raise your trucks using Riser Pads. Shockpads are usually lower and slightly softer than riser pads and additionally have a slight damping effect.
Riser and shock pads come in different heights, with the most common size being the 1/8 inch variety. Risers with a height of 1/2 inch are recommended for cruiser boards with soft wheels above 58mm diameter. If you are going to use riser pads, you will need to adjust the length of your mounting hardware to match the height of your pads. For 1/8 inch high pads, you will need bolts at least 1 inch long. This scale can be used for all other types. (For 1/4" risers you need 1 1/4" screw length, for 1/2" risers you need 1 1/2" screw length).
At Freedom Skateshop you will find a well-stocked selection of riser pads from all major brands like Pig, Independent, Diamond or Modus.