The problem is simple, as it is more dangerous to drive two cars side by side, whether side by side with a large car or a small car. Once there is an accident in the car next to you and the direction suddenly turns, you can't avoid it. If you want to avoid the obstacles ahead, you have nowhere to go. The other two vehicles traveling in parallel will be disturbed by the airflow emitted by the other vehicle, making the vehicle unstable and difficult to control. Therefore, the shorter the overtaking time, the better, and reduce the time spent traveling side by side. There is also a situation because of the road conditions. There are obstacles or decelerations ahead. If you want to overtake the next car before reaching the obstacles, the time requirements are also short.
If you want to overtake quickly, you have to give the car enough power and torque. Since the torque of the low speed gear is greater than that of the high speed gear, it is necessary to downshift to get more torque. Why is the low speed torque greater than the high speed gear torque? This involves the issue of gear ratio. The power of the engine is transmitted to the wheels through the gearbox. It is understandable that in low gears, small gears drive large gear rotation. The pinion requires only a small force to make the large gear start to rotate, but after the pinion turns several times, the large gear can only turn once; in the high-speed gear, the large gear drives the pinion to rotate, which requires a relatively large force to make the pinion rotate, but if the large gear rotates once, the pinion will rotate multiple times.
Is it downshifting when overtaking? What gear does it hang in? It should be determined based on the speed at the time and the power you need. If you're driving relatively fast and it doesn't feel like it's difficult to overtake, you don't need to downshift. If you find it a little difficult to overtake, when you step on the throttle too deeply, you feel that the car is not responding, you want to overtake quickly, you need to downshift.
Usually, you can downgrade up to one or two gears. Depending on the speed at the time, do not downshift too much, which can damage the engine. If the speed is 100 km/h, there is plenty of power when it is down to 4th gear. Do not lower to second gear. Engine speeds can suddenly be very high, even over the red zone and damage the engine. If the speed is 60km/h, it can be reduced to 4th or 3rd gear without damaging the engine. In fact, in most cases, reducing the power of one gear is enough.
The current autobox also has a downshift program. When the throttle is suddenly pressed and the acceleration is rapid, the transmission automatically downshifts and increases torque without the need for manual downshifting.
The above is an analysis of why you should downshift when overtaking. Some novice drivers will get it wrong. They think the gear is high and the car runs fast. If they want to overtake, they have to go upshift. This is completely wrong. If you want to overtake, don't step on the throttle for half a day. If you don't have enough momentum, you have to downshift.