Why is it necessary to shift gears?
3 Answers
The reason for shifting gears while driving is to frequently change gears according to actual conditions (except on highways) to save fuel and improve engine efficiency. On highways, when quickly accelerating to speeds above 60 km/h, the 5th gear is generally used with minimal shifting required. However, gear shifting becomes necessary when road conditions are poor. When driving on urban roads, rural roads, or mountain paths, gear shifting should be more frequent to select appropriate speeds based on road conditions. Below are precautions for driving on highways: 1. Drive in the designated lane: Highways have clearly marked lanes for large vehicles, small vehicles, etc. After overtaking, promptly return to your original lane and avoid occupying other lanes for extended periods. Additionally, emergency lanes should not be occupied without special reasons. 2. Maintain safe speeds and avoid speeding: The dangers of speeding are well-known, as it can lead to irreversible consequences both on local roads and highways. 3. Maintain safe following distances: Under normal conditions with dry roads and good braking, the following distance (in meters) should not be less than the speed (in km/h). For example, maintain at least 80m at 80 km/h and 100m at 100 km/h. Always pay attention to roadside distance markers. In rainy, foggy, snowy, or wet road conditions, the following distance should be doubled. 4. Observe traffic signs: Always pay attention to roadside and overhead signs and markings, and drive appropriately to the right to avoid crossing the right lane divider, allowing sufficient lateral distance for overtaking vehicles. 5. Do not occupy emergency lanes unnecessarily: Traffic accidents are inevitable on highways. If other vehicles cause lane blockages due to accidents, avoid occupying emergency lanes arbitrarily, as this may hinder rescue operations. 6. Avoid fatigue driving and take timely breaks: Fatigue driving is extremely dangerous on highways. When fatigued, reaction times decrease, making it difficult to respond correctly to emergencies.
I think shifting gears is essential when driving, mainly to better adapt the engine's output to changes in vehicle speed. For example, when starting off, shifting to a lower gear provides greater engine torque, making it easier for the car to accelerate from zero, avoiding stalling or sluggishness. At high speeds, shifting to a higher gear reduces engine RPM, ensuring a smoother ride and better fuel efficiency. In congested urban areas, frequent gear changes help reduce jerky movements, making the drive more comfortable. Although automatic transmission cars shift gears on their own, manual transmissions give me a better understanding of the car and add a bit of fun to the driving experience. Related to this, the original purpose of transmission design was to adjust gear ratios to protect the engine from overload, similar to a bicycle's gear system—using a low-speed chain for climbing hills to save effort and a high-speed chain for flat roads to go faster.
From a mechanical perspective, the core of gear shifting is to optimize the matching between engine speed and wheel speed. The engine operates most efficiently within a specific RPM range, such as 2000 to 4000 RPM being the fuel-saving zone; however, a direct connection to the wheels would cause either excessively high RPM at low speeds or insufficient RPM at high speeds. The gear settings in the transmission address this: lower gears like 1st or 2nd have larger gear ratios, providing high torque for starting, climbing, or carrying loads; higher gears like 5th or 6th have smaller gear ratios, reducing RPM during high-speed cruising to save fuel. I also found that on slopes, timely gear shifting can utilize engine braking to reduce the burden on the brakes, which not only extends component lifespan but also helps prevent accidents.
