IATF16949 12.25*2.5 Inch Electric Trailer Brake Shoes For Torsion Trailer Axles

A hydraulic braking system is a brake pedal attached to a piston full of a nearly incompressible brake fluid connected to another piston near the wheels attached to brake pads which push on the rotors on a wheel. When you push down on the brake pedal of a car, you make some fluid pressure P=Force/Area where the force is the force of your foot on the pedal (equalt to the force of the pedal back on your foot) and the area is the cross sectional area of the piston. That pressure is a lot higher than the pressure of your foot on the pedal, because the foot-pedal contact is much more spread out than the little piston area. Fluids will transmit pressure throughout the whole fluid, so the piston at the other end will push harder on the brake pads, pressing them against the rotors. The friction between them causes the rotational energy of the wheels to turn to heat and stop the vehicle.

Since the brake fluid is nearly incompressible, you don't have to press the pedal far to make the pressure go way up. Squeezing liquid into just a bit smaller volume makes a big difference in pressure. (If air gets in your brake system, then you have to push the pedal much farther because air is very compressible.)