What are the two main methods to know when to shift gears in a vehicle?

The two main methods to know when to shift gears in a vehicle are based on engine speed (measured in revolutions per minute, or rpm) and road speed (measured in miles per hour, or mph). Monitoring the engine speed helps the driver determine when the engine is operating at optimal levels; shifting too early or too late can negatively impact vehicle performance and fuel efficiency. Generally, drivers want to shift gears before the engine reaches its maximum rpm to avoid over-revving, which can cause engine damage.

Road speed is also a critical factor because different gears provide varying power and speed ranges. Understanding when to shift based on how fast the vehicle is moving ensures that the engine operates efficiently and provides the necessary power for acceleration and maintaining speed.

The other methods listed do not primarily guide gear shifting in conventional driving scenarios. Temperature and pressure readings might relate to engine performance but do not directly indicate when to change gears. Gear position and fuel efficiency are not direct indicators of shifting timing since they depend on multiple other factors. The sound of the engine and speed of the wheels may provide some cues, but they are not as precise or consistent as monitoring engine and road speed.