What T^2 said is true given your robot remains completely flat on the floor, parallel with the carpet, and doesn't weigh too much. In the event you're not parallel (ie. being pushed from the side and slightly tipped upwards on the pushing end), the W tread will grip to the carpet like cleats. It won't need to be a significant lift, but anything to change the robot from parallel with the floor will engage cleat mode.

Source: Experience with cleat mode this year.