The optimal gear shift speed for an automatic transmission depends on the vehicle type, model and driving style. However, as a general rule, here are the approximate ranges:
Gearbox with 4-5 gears:
* 1st gear: 0-15 km/h (0-10 mph)
* 2nd gear: 15-30 km/h (10-20 mph)
* 3rd gear: 30-50 km/h (20-30 mph)
* 4th gear: 50-70 km/h (30-45 mph)
* 5th gear: 70 km/h and above (45 mph and above)
Gearbox with 6-8 gears:
* 1st gear: 0-10 km/h (0-6 mph)
* 2nd gear: 10-20 km/h (6-12 mph)
* 3rd gear: 20-30 km/h (12-20 mph)
* 4th gear: 30-50 km/h (20-30 mph)
* 5th gear: 40-60 km/h (25-40 mph)
* 6th gear: 50-80 km/h (30-50 mph)
* 7th gear: 60-100 km/h (40-60 mph)
* 8th gear: 80 km/h and above (50 mph and above)
Please note that these values may vary depending on vehicle and driving conditions. The transmission typically changes gears based on vehicle speed, engine load, and other factors.