We run small wheeled mid lifts, very easy to overload the mid lift if the 5th wheel is too far back!!!, yes you read that right it works contra to how you’d expect on some vehicles.
I used an axle weigher and trial and error to get the 5th wheel in the ideal spot for axle weights, luckily at that setting it will pull every trailer we have.
If you have use of a normal weighbridge and a helpful geezer in the office you can work out the individual axle weights by checking the GVW then driving one axle after another off the bridge, writing down the weight left each time then get subtracting, not as accurate as an axle weigher but not far out either.
I move mine regularly depending on the trailer. Not too close to smash the lights on the unit with the legs but enough for easy manoeuvre without snagging lines.
Experience helps as well 
Juddian:
We run small wheeled mid lifts, very easy to overload the mid lift if the 5th wheel is too far back!!!, yes you read that right it works contra to how you’d expect on some vehicles.
I used an axle weigher and trial and error to get the 5th wheel in the ideal spot for axle weights, luckily at that setting it will pull every trailer we have.
If you have use of a normal weighbridge and a helpful geezer in the office you can work out the individual axle weights by checking the GVW then driving one axle after another off the bridge, writing down the weight left each time then get subtracting, not as accurate as an axle weigher but not far out either.
Your theoretical wheelbase is from the center of your front axle to a point between the drive and the midlift. If your drive was rated at 10t and the midlift 7t, then divide between the 2 axle center into 17, the theoretical point would be 7 in front of the drive and 10 behind the midlift. That’s why moving the fifth wheel forward so it’s over the top of the midlift actually takes weight off the midlift
stevieboy308:
Juddian:
We run small wheeled mid lifts, very easy to overload the mid lift if the 5th wheel is too far back!!!, yes you read that right it works contra to how you’d expect on some vehicles.
I used an axle weigher and trial and error to get the 5th wheel in the ideal spot for axle weights, luckily at that setting it will pull every trailer we have.
If you have use of a normal weighbridge and a helpful geezer in the office you can work out the individual axle weights by checking the GVW then driving one axle after another off the bridge, writing down the weight left each time then get subtracting, not as accurate as an axle weigher but not far out either.
Your theoretical wheelbase is from the center of your front axle to a point between the drive and the midlift. If your drive was rated at 10t and the midlift 7t, then divide between the 2 axle center into 17, the theoretical point would be 7 in front of the drive and 10 behind the midlift. That’s why moving the fifth wheel forward so it’s over the top of the midlift actually takes weight off the midlift
Our problem being just how low the max weights are on small wheeled mid lifts, circa 5.3 tons if recall correctly on mine (edit 5.2), pretty sure some of the other makes are lower still, not a lot to play with.
It’s not something i’d come across before getting a small mid lifter cos axle weights were less of an issue with normal layouts than trying to perfect the best handling position, never would i have dreamed moving the fifth wheel back would increase the weight of the mid lifter, just assumed as with a 2 axle tractor it would increase the drive axle weight…took a bit of moving it back and forth before i convinced mesen it was real.
merc0447:
We used to have air operated 5th wheels that you operated from in the cab. Pain in the ■■■■ so they where. And if you forgot to lock it off the first time you hit the brakes the trailer would slam you forward 
My policy about 5th wheels is don’t [zb] about moving them, leave them be. It is a policy that has never caused me any problems.
+1
Should be locked in place so people who cant even put their lines away cant play with the 5th wheel positioning. Loose lines annoy me 
Back in 2002 I wrote a spreadsheet to calculate axle weights and swing clearances for a fleet with which I was involved. I took this further so that I could input the weight of soft fruit in a punnet, the weight of the punnet, the number of punnets in a box, boxes on a pallet, standard or euro pallets and the position of each pallet weight on the dimensions of ONE type of Gray and Adams fridge trailer. It assumed that the load was all one type of pallet. I have not looked at this for many years and the abbeviations used to describe what each cell refers to are now somewhat of a mystery. However there were a number of variables which made it relevant to the specific vehicles measured and also assumptions made (see 3 & 4 below). The ones which immediately spring to mind are:
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The make and model of fifth wheel slider is important as is the position of its subframe on the chassis. Different models of slider have different distances between the notches.
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For a six wheel unit there is a criterion called the theoretical wheelbase, this is a calculation based upon the distance between axles 2 and 3 and their plated weights.
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The weight carried by axle 2 is dependent upon the air bag pressure in axle 3 and upon how the manufacturer has set up the system. The ‘value’ of weight/air bag pressure upon axle 3 which triggers weight transfer to axle 2 and the ratio of that transfer needs to be known. Of equal importance is the assumption that the vehicle was set up correctly initially and has not subsequently deviated from those settings.
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An assumption was made that each layer of product on a pallet was of even weight distribution.
Nos. 3 and 4 made this really only a theoretical exercise of limited practical value other than as a guide. However it did mean that given the correct data it is possible to devise something similar.
Well, as the 5th wheel was as far back as it would go (previous occupant, not my idea) I’ve moved it forward about 6" / 3 notches. What a difference to the handling it has made. The cab isn’t as bouncy anymore and it’s not feeling like it’s understeering all the time.
I didn’t actually think it would have made much difference at all but it has. Not had a max weight on it yet though.