Why Does the RPM Increase When Downshifting?

1 Answers
VanTyler
07/29/25 3:42pm
An increase in RPM during downshifting is a normal phenomenon. Below is a detailed explanation of why the RPM increases when downshifting: 1. Reason: There is a difference in the diameters of gears on the same shaft, so gears rotating simultaneously on the same shaft will have different RPMs due to their varying diameters. 2. Example: Taking a 4-speed automatic transmission as an example, when driving at 80 km/h in D gear, the RPM might be around 2000. At this point, if the gear lever is shifted to 3rd gear, the ECU will issue a command for the transmission to only switch between 1st and 3rd gears. Therefore, when shifting to 3rd gear, since the gear ratio of 3rd gear is larger than that of D gear (4th gear), the transmission's RPM cannot keep up with the driver's speed demand, so the RPM will increase to maintain the vehicle's speed. This is also why, when overtaking with an automatic transmission, shifting to 3rd gear is often used to increase the engine RPM for the purpose of overtaking.
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