Old John:
Star down under.:
Unlike our friend Carryfast, I won’t claim ultimate expert status, but I will speculate, based on Australian legislation. Overhang is dictated by the wheelbase, in our situation overhang cannot exceed 60% of the wheelbase. As your (U.K.) road system is generally narrower and more crowded than ours, you seem to have smaller wheelbases on similar length trailers to us. By allowing longer trailers whilst maintaining existing cut in dimensions, which are quite probably legislated, an extra axle will have to be added, to technically reduce the overhang. Trailers can be built with enough strength to support the extra length and any driver/loader with a modicum of intelligence, can load said trailer appropriately so as not to lift or impose rediculous weights on axles, as suggested by Carryfast. As the rearmost axle is only placed to comply with existing legislation, it has created its own wheelbase to the axle/s forward of its position. To eliminate excessive tyre and bearing wear the rearmost axle will need to comply with the sweep of the overhang, either by means of a simple castor steer or a more complex, heavier and maintenance intensive positive steer.
I finished my apprenticeship.In UK, the maximum permitted overhang is also 60% of the wheelbase, on rigids at least, I’m not certain if trailers are the same.
When the maximum length of trailers in this country was permitted to be increased to 13.6 metres, the turning circle (wheelbase) was required to remain the same as the previously permitted 12.5 metre trailers, so trailers are now built with longer forward overhangs, (1.6 m ahead of the pin) and slightly longer rear overhangs also.
When permitted maximum weights (under C+U regs) were increased from 41 to 44 tons for six axle outfits, the extra weight was/is required to be borne by the tractor unit. No increase in trailer axle weights is permitted. (Currently 8 tons per axle)
Really interesting thanks