electric bicycle or vehicle speed depends on one parameter
“the voltage”

In the electric bicycle segment, the motors are usually available at a voltage of 24V, 36V, 48V, and even on 60/72V

depending upon the voltage supplied to the motor, you can achieve the respective speed.

one more thing, when the supply voltage is more than the rated voltage can cause major damage to the motor. which is normally we have to avoid.
the maximum speed we can achieve in an ebike is about 31mph or 50kmph at motor power of 1.5Kw
to understand voltage vs speed, see the table ‘A’