This must be a joke, i personally find 31mph law Stupid, how are we ment to cope on 40mph zones ? when people overtake you etc. ? most EU countries allow 14-15year olds to have 50cc bikes which are de-restricted, you are even allowed to carry a pillon. and yet in UK you have to have a full moped licence and you still can only do 31? so how on earth you can hit the 31mph limit with a passanger ? not even talking about a Small hill.
its as simple as fitting a rev restrictor which activates every time the bike starts. that way once oon the dyno it will top out at what ever speed you choose