A wellbore rig top drive is disclosed. The wellbore rig top drive can include a main bearing housing. The wellbore rig top drive can also include a main bearing supported by the main bearing housing. The main bearing can be configured to support a weight of a wellbore string and facilitate rotation of the wellbore string about an axis. The wellbore rig top drive can further include a quill supported by the main bearing and configured to rotate about the axis. The quill can be coupleable to the wellbore string. In addition, the wellbore rig top drive can include a drive motor disposed below the main bearing and supported by the main bearing housing. The drive motor can be coupled to the quill to provide torque to rotate the quill about the axis.