Is 25 mph in third gear a gear mismatch?
2 Answers
25 mph in third gear is a gear mismatch because third gear typically requires a speed range of 30 to 50 mph. Below is an introduction to the corresponding speeds for different gears and the effects of speed and gear mismatch. Corresponding speeds for different gears: For starting in low gear, first gear is generally used, with an economical speed of 15 to 20 km/h; second gear has an economical speed of 25 to 40 km/h; third gear has an economical speed of 40 to 60 km/h; fourth gear has an economical speed of 60 to 75 km/h; fifth gear has an economical speed of over 75 km/h. Effects of speed and gear mismatch: If a speed and gear mismatch occurs during a test, the only option is to fail and retake the exam. Frequently doing this in actual driving increases wear between the transmission gears and can also damage the clutch. The consequence of high gear at low speed is stalling the car and causing engine shudder.
Speaking from my experience as a veteran mechanic with over a decade in the field: In a manual transmission vehicle, driving at 25 km/h in third gear can indeed lead to gear mismatch. At this speed, the engine RPM may drop below 1,000, causing the engine to struggle with insufficient load, much like hauling a heavy load. This situation often occurs in traffic jams or when climbing hills. Persisting in this manner not only makes for an uncomfortable drive but can also lead to burnt ignition coils or clutch wear. I've inspected numerous vehicles where prolonged high-gear, low-speed driving resulted in premature engine failure. It's advisable to downshift to second or first gear at low speeds, keeping the RPM above 1,500 for smoother operation. Regularly checking the tachometer can greatly prevent such issues, as vehicles are designed for smooth driving.
