Stepper Motors (NEMA-17) Won't Run When Wheels Are Attached
Are the wheels simply too heavy for the motors?  Or in more precise physical terms, is the moment of inertia of the wheels so great that the stepper motors are not powerful enough to turn them?

Stepper motors tend to "tick" from one position to the next.  This implies a very rapid acceleration, and then deceleration, of whatever is attached to the motor.  If that's a heavy wheel, the motor may just stall instead.

Increasing the motor current may help.  But not so much that you burn out the motors.