Which type of brakes goes to a brake pedal reserve of 2"?

The correct choice indicates that conventional brakes (also known as non-power brakes) have a brake pedal reserve of 2 inches. This measurement refers to the distance the brake pedal can be pressed before the brakes fully engage. In conventional brake systems, which rely entirely on human force for actuation without any assistance from hydraulic or vacuum systems, the brake pedal typically has a manual application that requires a substantial amount of physical effort to apply the brakes effectively.

Power brakes, on the other hand, utilize a power boost, most commonly from vacuum sources, which reduces the amount of effort required by the driver to engage the brakes. Consequently, such systems may not adhere to the same reserve specifications as conventional brakes due to their design, which often compensates for less physical effort.

Hydraulic and pneumatic brakes operate on different principles. Hydraulic brakes use fluid pressure generated by the brake pedal to engage the brakes, while pneumatic brakes utilize compressed air, typically used in larger vehicles. Each of these systems has different actuation characteristics and pedal reserves which do not match the specifications unique to conventional brakes.

In summary, the distinction in the reserve measurement arises from the method of engagement and power assist, making conventional brakes the type that specifically aligns with the given reserve measurement.