In continuing tests, I managed to tag the flange on the rear pulley and completely crack it off.  Oops!  What did I hit?  The little bump at the beginning of the driveway ramp through a sidewalk.  

This thing. 

So no, the wheels are not big enough, for this and several other reasons.  

However, in the interest of continued learning, I will keep moving forward with the current design, building out the steering column next so we can all see an e-scooter actually fit in half the space of a normal backpack.