Join Date: Nov 2011
Location: Springfield, MA
Bikes: 2012 Motobecane Fantom CXX, 2012 Motobecane Fantom CX, 1997 Bianchi Nyala, 200? Burley Rock 'n Roll
Since the consequences of a hitch failure are substantial (at minimum, loss of the hitch and probably severe damage to the rack and whatever bikes are on it), it makes sense to go with Class II or higher if it's available for that car. Better safe than sorry.
Also, I haven't weighed my kids' bikes, but they sure feel just as heavy as our adult bikes.