Why is driving at 80 km/h in fourth gear more fuel-efficient than in fifth gear?
2 Answers
The reason why driving at 80 km/h in fourth gear is more fuel-efficient than in fifth gear lies in: 1. Driving in fourth gear generally keeps the engine speed at around 2000 RPM, which is an ideal operating range; 2. Driving at 60 km/h in fifth gear further reduces the engine speed, theoretically making it more fuel-efficient and quieter, but it is detrimental to the engine. Incomplete fuel combustion, power lag, sluggish acceleration, and increased carbon buildup can occur. Additional information: Introduction to driving in fourth gear is as follows: 1. Generally, the optimal shift timing for most cars is when the engine reaches 2000 RPM, preferably not exceeding 2500 RPM. For some high-displacement, high-power engines, the peak efficiency range may be slightly delayed, so shifting around 3000 RPM can be considered. 2. Different vehicles perform differently in terms of engine and transmission characteristics. Drivers can identify the optimal shift timing by listening to the engine sound. A dull engine sound usually indicates it's time to upshift. Driving in a gear that's too low increases engine stress, raises fuel consumption, and significantly impacts both the engine and transmission.
I've been driving for most of my life, and every time I cruise around 80 km/h on the highway, I like to test the fuel efficiency in fourth gear. Surprisingly, it turns out to be noticeably more fuel-efficient than fifth gear. This is because engines operate at varying efficiencies at different RPMs—too high and they guzzle fuel, but too low can also drag down efficiency. At 80 km/h in fifth gear, the engine usually runs at a low RPM, around 1800, feeling underpowered like it hasn't had enough to eat, requiring more throttle to maintain speed, which ironically burns more fuel. In fourth gear, the RPM climbs above 2500, placing the engine right in its sweet spot where fuel injection and combustion are more uniform and efficient, much like finding the perfect stride when running. My old Toyota is the clearest example—on long trips, I stick to fourth gear, watching the fuel gauge drop at a leisurely pace. This also depends on the car model; automatics might be tuned more intelligently, but manuals give you more control, which is more satisfying. Ultimately, fuel efficiency hinges on matching engine load—experiment a few times to find your car's sweet spot, balancing safety and savings.
