Previously, vehicles did not have synchronizers, especially some trucks that needed to add a foot of oil when downshifting, increase the engine speed to match the speed of the gearbox, in order to shift smoothly, otherwise the gear would not be easily engaged. Nowadays, cars have synchronizers, and as long as the speed and gear are not too mismatched, they can smoothly engage. Is downshifting and refueling still meaningful? Under what circumstances is this operation necessary?

        
     First of all, what is a downshift refueling? When downshifting from high gear to low gear, before preparing to shift to low gear, press the accelerator pedal lightly, and then shift to continue driving. Pressing the accelerator pedal lightly will replenish the fuel. Why do you need to operate like this? Because at the same vehicle speed, the engine speed varies with different gears. For example, the current 5th gear speed is 80km/h and the engine speed is 1800 rpm. If you want to downshift to 4th gear, the engine speed must be much higher than 1800 rpm, which may reach 2400 rpm. This creates a speed difference of 600 revolutions.

        
      There will be two impacts, one is that the vehicle will experience significant jerks. Due to a decrease in gear, the engine will generate a certain amount of braking force, causing the vehicle speed to rapidly decrease. At this point, the fuel gate will continue to drive, and the car will suddenly charge forward. The feeling is that the vehicle is very unstable. If a foot of oil is added and the 600 rpm difference is added, the engine will reach 2400 rpm after downshifting and releasing the clutch. This way, the engine will not generate braking force and will be very stable at this time.

        
     The second reason is that the acceleration time is delayed. For example, when entering a large bend, you should slow down before entering the bend, and before leaving the bend, you should shift the gear to the right gear and accelerate by pressing the accelerator. At this point, the engine should be kept at a high speed in order to unleash torque. If the engine is at a high speed, it needs to be put into a low gear. At this time, a little oil needs to be added to smoothly put it into gear, and it can quickly increase speed when turning. Of course, this point can be used by drivers running on the track, but it is not commonly used for driving, so there is no need for such intense driving.

        
Now downshifting and refueling can still be used, generally suitable for overtaking. When accelerating, downshifting requires refueling operation, and when decelerating, it is not necessary. What does it mean? Firstly, we need to understand that when overtaking, lowering a gear will increase the torque of the car, accelerate faster, and overtaking will be smoother. For example, if you are about to overtake and you are in 5th gear, overtaking must be in a continuous refueling state, without the process of decelerating or retracting the throttle. At this point, you also need to downshift. If you don't add a little oil, there will be a speed difference as mentioned above, severe jerking, and a significant impact on the transmission, which is not good for both the car and people. After adding a foot of oil, you can quickly release the clutch, and then press the accelerator deeply to quickly overtake.
        
      Why can I not use it when slowing down? Because there is a process of decelerating by applying the accelerator and brakes, such as 80km/h in 5th gear, which has decreased to 50km/h, the vehicle speed and engine speed at this time are exactly matched with 4th gear. Shifting into 4th gear will definitely be smooth and there will be no jerking phenomenon. So as long as the gear is matched with the vehicle speed, there is no need to refuel. If the vehicle speed is high and the vehicle is in a low gear, there is a need to refuel.

From: WONDEE Autoparts 2023-10-9