Why Does the Car Jerk When Downshifting?
2 Answers
The reason a car jerks when downshifting is due to a mismatch between the engine speed and the current vehicle speed, meaning there is a difference in rotational speed between the engine and the clutch disc (in most cases, the engine speed is lower than the clutch disc speed). The engine serves as both a power generation device and can refer to the entire machine, including the power unit (such as gasoline engines, aircraft engines). Engine types include internal combustion engines (e.g., gasoline engines), external combustion engines (e.g., Stirling engines, steam engines), gas turbines (used in racing cars), and electric motors. The clutch is located within the flywheel housing between the engine and the transmission, secured to the rear plane of the flywheel with screws. The output shaft of the clutch is the input shaft of the transmission.
Having driven for many years, the jerking sensation during downshifting mainly comes from the mismatch between the engine and drivetrain speeds. When you shift from a higher gear to a lower one, say from fifth to third gear, the car speed is high, but the engine RPM is still low and can't keep up with the wheel speed. Once you release the clutch, the power transfer isn't smooth, causing the car to jerk abruptly. It's somewhat like suddenly hitting the brakes while running—your body lurches forward. I often remind beginners to blip the throttle: lightly press the accelerator before downshifting to raise the RPM to the matching point before releasing the clutch, ensuring the motion is smooth. If the car is an older model or the clutch is worn, jerking becomes more noticeable, and regular oil changes can help. Also, when it's cold, the fluids are thicker, requiring gentler operation. With more practice, driving becomes much more comfortable.
