No one really seems to giving you any answers here so i’ll fill you in a bit.
Firstly rear overhang is a very simple concept, remember the seesaw principle? How one weight can act a force upon another weight by using leverage, just as Archimedes said he ‘could move the earth if he had somewhere to stand’ weight on the rear overhang of your truck can lift weight off the front axle by using this leverage force. If you look at the VTG plate in the cab of the vehicle it will say the front axle can take something like 7500kg on the front axle and 11,200kg on the back axle, so obviously the rear wheels can take more weight but the front wheels are already carrying the weight of the cab and engine, so you will be lucky if you have any more that 4000kg of capacity left at the front.
So if you load a 4x2 rigid truck to maximum weight with all the weight between the headboard and rear axle you are extremely likely to overload the front wheels because you are putting around 11,500kg shared between the front and rear wheels, so there will be about half that weight or so on the front, just over 5 tons plus the weight of the cab and engine at say 3.5 tons would i imagine give an overload of perhaps up to a 1000kg or maybe a little bit more.
However, put the same load over the entire length of the vehicle and any weight put over the rear overhang will now counteract or act as a lever to lift weight off the front axle, making the same vehicle and load now legal to drive, simple - its just another one of Archimedes wonderful discoveries that we now all take for granted. The problem for drivers arrises when you take off part of the load on the rear overhang to deliver it, your vehicle which was previously legal is now overloaded after removing some of your leverage, so it may be best to put light loads to the front and heavy items further back. Also be wary of putting too much weight on the rear overhang as this can cause braking and steering problems if the front end gets too light.
As for the Module 4 test, there are 3 types of loads could be asked to point to where you would position them;
Half load of palletised paper, on a normal 18ton boxvan the sort you will likely be using for this test this will be equal to 6 pallets, you should point to distributing the load over the central 50% of the load area, point to just above the rear axle and towards the headboard by 3 metres (the length of 6 pallets side by side). This should avoid any chance of it overloading the front axle by positioning the load between the middle of the boxvan and rear wheels. With a half load there will be no need to put any of the weight over the rear overhang, now I know you will be leaving a gap between your load and headboard and thus the load should be adequately prevented from moving forwards.
Half load of steel plates, normally carried by flat bed trucks steel should always be loaded up to the headboard, unlike pallets that cannot be easily broken down and spread out steel plates will be the full length of your vehicle, a half load refers to you having a half stack, not a full say 5 plates. So the simple answer is to point to the full length of the vehicle.
Last one, Half load of empty roll cages, easiest one of all, they are empty! so weigh virtually nothing, you can position these up to the headboad because they will not overload the wheels at the front of the truck but they do move around if they are not pushed up against the inside walls of the truck, they may move or fall during driving making unloading dangerous.
Hope to have been of help, all these answers work fine for us, which we gained them from getting hold of the driving examiners answer sheets!
BTW, artic trailers often do have overhang just the same to take weight off the fifth wheel, but tipper trucks don’t need to because they have 2 axles at the rear, both with double tyres and two front axles making overloading due to poor load positioning much less of problem, plus tippers normally carry only full loads of muck, aggregates etc spread out evenly.
