Got a text off Dad yesterday to say they'd had a lift with the owner of the resort in Sai Yok to just north of Bangkok. They then got on their bikes and cycled along route 9 and they are now in Sena which is just to the west of Ayutthaya. Looking on Google Maps they probably did around 85 kms on the bikes so will let them off having a lift! They are planning on having two nights in Sena as there are quite a few tourist things to do.
Tried a Skype call earlier but Dad was out in a TukTuk doing the "tourist" things and then out for a meal. Possibly missed chatting to him now, but I've sent him a couple of texts to let him know that Brad had won the Time Trial and Paris-Nice so he'll probably be having a pint to celebrate that win!