What is the relationship between engine speed, vehicle speed, and gear in a car?

[ClaytonFitz]

The relationship between engine speed, vehicle speed, and gear in a car is pairwise correspondence. Here are the introductions about the three: 1. The relationship between engine speed and vehicle speed: Engine speed and vehicle speed do not have a one-to-one correspondence, but also depend on the current gear, which is the speed ratio of the transmission. 2. The relationship between vehicle speed and gear: The recommended speed for each gear is about 15 km/h for 1st gear, 25 km/h for 2nd gear, 35 km/h for 3rd gear, 55 km/h for 4th gear, and 65 km/h for 5th gear. 3. The relationship between engine speed and gear: When the engine speed remains unchanged, the higher the gear, the faster the vehicle speed; the lower the gear, the slower the vehicle speed.

[May]

The relationship between engine speed, vehicle speed, and gear is closely interconnected. Simply put, how fast the engine is running, how quickly the car is moving, and which gear is being used all influence each other. Engine speed is like a person's heartbeat, while the gear controls the way power is delivered. The higher the engine speed, the more intense the engine's operation and the more fuel it consumes. When the vehicle speed increases, if you stay in a low gear, the engine speed will rise sharply. At this point, you should shift up to bring the engine speed down. Conversely, when climbing a hill, the vehicle speed may not be high, but maintaining a higher engine speed is necessary for sufficient power. Personally, I prefer to shift gears by watching the tachometer, usually shifting up around 2000 RPM for the smoothest transition. Automatic transmission cars adjust gears automatically based on vehicle speed and throttle input. Maintaining the right balance between engine speed and gear not only saves fuel but also protects the engine from premature wear, especially during highway cruising, where using the highest gear to maintain low engine speed is the most economical.

[DelPenelope]

I think the most direct feeling when driving is the interaction of three elements: pressing the accelerator increases the engine speed, but the change in vehicle speed depends on the gear. In lower gears, the engine speed rises quickly but acceleration is limited—for example, in first gear, even at 4000 RPM, the speed might only reach 30 km/h. Shift to third gear at the same RPM, and the speed could hit 60 km/h. Downshifting for overtaking is the most exciting part. For instance, at 80 km/h in fifth gear with 1500 RPM, suddenly dropping to fourth gear will make the engine jump to 2500 RPM, roaring to unleash its power. In daily driving, it's important to match gears to road conditions: use lower gears with higher RPM for starting at traffic lights in the city, and higher gears with lower RPM for cruising on highways. Remember the risks of untimely gear shifts: failing to upshift when needed will make the engine scream and waste fuel, while not downshifting when necessary can lead to insufficient power or even stalling. My experience is to listen to the engine sound and watch the dashboard—it protects the car and makes driving smoother.

[LaZoe]

The core relationship between RPM, speed, and gear lies in the transmission ratio difference. The engine converts RPM into speed through the gearbox, with each gear having different ratios: a large first gear ratio might make 2000 RPM translate to only 20 km/h, but with greater power; whereas a small fifth gear ratio allows 2000 RPM to reach 80 km/h. Automatic transmissions use the ECU to calculate the optimal match, while manual transmissions require the driver to time shifts correctly. My manual driving habit is to shift based on speed: shift to second at 20 km/h, third at 40 km/h, fourth at 60 km/h, and fifth at 80 km/h. This keeps RPM mostly within the economical range of 1800-2200 RPM. If power feels insufficient uphill, immediately downshift to raise RPM above 3000, and you'll instantly feel a surge of continuous power.