Kinematic viscosity is a key characteristic of brake fluid since the system must operate smoothly within a wide range of temperatures. Fluids such as honey, for example, increase in viscosity as temperatures fall and decrease in viscosity as temperatures rise. To put some numbers to it, consider that the viscosity of water at room temperature is around 1.0 mm 2/s and the kinematic viscosity of honey is around 6,900 mm 2/s.įor most fluids, viscosity tends to change depending on temperature. So, a fluid with a high kinematic viscosity tends to run slowly (as with the honey) and a fluid with low kinematic viscosity tends to run fast (think of water). The more time it takes, the higher the kinematic viscosity. Kinematic viscosity is a measure of how slowly the honey pours out. In less-complicated wording: Imagine taking a jar of honey and pouring out all the honey. It’s measured in squared-millimeters per second (mm 2/s), also known as the unit Centistokes abbreviated as cSt. Kinematic Viscosity is a measure of how much the fluid resists flowing under the force of gravity. Viscosity of a fluid, in simple terms, is how thick the fluid is. We’ll get into how later on in this article. When we talk about brake fluid, incompressibility is related to the boiling point of the fluid. The efficient transfer of pressure relies on the incompressibility of the brake fluid. Drum brakes work in much the same way.įor the system to work efficiently, the brake fluid must be able to move easily through the lines ( kinematic viscosity) and must be able to efficiently transfer the pressure from the master cylinder to the piston. The pistons in the calipers then convert that pressure to a force that clamps down on the rotors. That pressure is transferred from the master cylinder to each caliper, through the brake fluid. The schematic shows how the brake fluid (light orange) is the medium in which force is transferred without a brake booster. The force of the pedal gets converted to pressure through the master cylinder.