I'm talking to a Wilson dealer in ON and he insists even 48 ft trailers here are required to comply with the bridge/wheel base formula. According the Ontario Highway Traffic Act, the maximum wheelbase of a semi-trailer (king pin to the middle of the tandems on the trailer) can only be between 6.25 to 12.5m. 12.5 M is 41 FT. Only trailers built before 2006 that are 48 ft in length are exempt from this requirement till 2020 here. So, a new 48 ft trailer cannot have more than 41 ft from the kingpin to the middle of the trailer axle group.

what distance you allowed from centre of tandem to rear of trailer in states and overall length of rig bumper to bumper

Here in Canada where I live (Ontario) the overhang is limited to 35% of your wheelbase (the wheelbase is measured from the truck's kingpin to the center of the axle group on the trailer). The maximum trailer length is 16.2 M or 53 FT. The truck's wheelbase cannot be more than 6.2 M or 244", which often makes it impossible for US drivers to come here. Their trucks are usually longer than the ones we have in Canada.

just looked up our specs:max overhang 4mtrs or 5o% of wheelbase measured same as yours ours is 8.5mtrs max ,18metres bumper to bumper no truck lengh restrictions. for 44ton 7 axles either 3trk 4trlr ,4trk 3trlr, or 4and4