What are the two ways to know when to shift gears?

The correct answer focuses on the importance of understanding both engine speed (rpm) and vehicle speed (mph) when determining the appropriate time to shift gears.

Engine speed, measured in revolutions per minute (rpm), indicates how hard the engine is working. Each vehicle has a specific rpm range where it operates most efficiently. Shifting at the right moment ensures that the engine runs smoothly without over-revving or lugging.

Vehicle speed, measured in miles per hour (mph), informs you of the current speed of the vehicle. This is crucial when shifting gears, as it helps ensure that you maintain optimal performance and safety, particularly when accelerating or descending hills.

The combination of these two measurements allows for better control over the vehicle and enhances fuel efficiency, overall performance, and safety on the road.