Hello. Does anyone know what the usual voltage rating for motors like these is? They're commonly found in small toy cars and other small devices.
A clue would be the batteries used by the toy.
Commonly 3 V.
Brushed DC motor voltage rating is purely nominal. Exceeding the manufacturer's rating simply shortens the life of the motor.
Stalling the motor is likely to give more problems than a few more volts...
So, indeed, try 3 or 5 V. Most toys do not have more than 4 1.5V batteries...