The main role of piston rings in cars is to regulate the amount of oil cars consume. Piston rings form seals around combustion chambers, which allows them to transfer heat to cylinder walls. To form the seals, piston rings use a combination of pressures, called inherent and applied pressures.
Inherent pressure refers to an internal force that puts outward pressure on the surrounding chamber. Pressure builds within piston rings and exists as a spring force. This force ultimately releases within the chamber, and expands the surrounding piston rings to different widths, which vary depending on the materials used to construct the chambers and piston rings. The free piston ring gap, which refers to the distance between two ends of the piston rings in a relaxed state, determines the amount of inherent pressure present in the chamber. Greater amounts of space between the two ends of piston rings create larger amounts of force released by piston rings into surrounding chamber spaces when triggered. In addition to inherent pressure, piston rings use applied pressure to operate. Applied pressure consists of the forces created by combustion gases exerted on piston rings. The pressure of these forces in turn causes the rings to expand. The type of piston rings varies among cars with those with small engines containing rings in the form of compression, wiper and oil rings.