Righto this is a follow on thread from the one i recently started about grip issues, titled Intelligent Desirable Drivers Please Help, mainly applying to artics but can also apply to other vehicles with tag or mid lift axles.
In that thread Stevieboy308 posted about dropping the trailer right down and also raising the tractor unit to full height, in order to shift some extra weight onto the tractor unit…
…in the other thread we discussed lifting the unit mid lift (or rear tag) or at least dumping the air from it (as some don’t actually lift) in order to transfer some weight onto the drive axle.
We also discussed switching off TC or ASR to enable drive to be maintained to keep going and save the clutch, because with the traction control or ASR engaged soon as the vehicle detects any wheelspin it cuts the power, a bad thing.
We also discussed the use of diff lock, and to be bloody careful with it if the surface is grippy (arguably if its grippy it won’t be needed) but no two set of circs are the same and so you learn your own lorry and make judgements as to what you need and what you don’t at the time.
All clear so far? good 
Right thinking caps on, cos this is stretching my pin sized mind to explain the bugger, and gawd nose what you’ll make of it, heads down here we go 
Righto, today i tried Stevieboys suggestions with an empty lorry and with another lorry loaded.
Both are general artic powder tanks, both have lifting mid lifts not as makes any difference for this report, any trailer lifting axles left down for weighing to make it the same configuration for all weights, with me?
Basically, tractor unit only on the weighbridge and performed 2 weights with the empty vehicle, 3 with the loaded vehicle.
Empty lorry tared @ 15140
Loaded lorry grossed at 42600.
1st weight was tractor in normal condition, makes no difference whether the mid lift is up or not…i’ll come to that as an after explanation…
2nd weight was tractor with trailer air dumped…i also released the parking brake after dropping then re-applied it cos the vehicle park brake works on the trailer too and suspension issues would have affected weight shifting.
3rd (with loaded vehicle) was with the tractor unit at max height.
Empty lorry.
1st weight tractor unit in normal state 9960 kgs
2nd weight, trailer air dumped, tractor at full height, 10220kgs.
remember the lift axle was down for this experiment, its possible there might have been larger gains had the front lifter of the trailer been up, certainly there would have been more weight on the tractor regardless.
Loaded lorry.
1st weight, tractor unit in normal state 19460
2nd weight, trailer air dumped, tractor at normal height 22220 
3rd weight, trailer still dumped, tractor at full height 22480.
So there you are, proof indeed of Stevieboys advise being spot on, not as we doubted it but nice to see the results.
The biggest gains are of course loaded, with a massive 2760kgs extra weight transferred to the tractor and if you raised the unit to full height, you gain a full 3020 kgs extra, i’m quite shocked to be honest, and rather disappointed in meself i’d never thought of it before, idiot i am 
So when you’re spinning merrily in the snow and wondering what you can do, remember this neat little trick.
Now i mentioned raising the mid lift of the tractor unit, or in the case of Scanias etc at least dumping the air cos loaded the axle won’t raise fully, but the gains will still be massive.
I use an axle weigher regularly so know what gain there is with mid lift up or with air dumped when loaded.
So if you have a standard artic with mid lift, and raise the lifter, the weight of the unit drive axle goes up from approx 9.5/10 tons up to around 12.5/13.5…cos obviously some of the weight is transferred onto the steer axle.
Thinking this further, if you were stuck somewhere and lifted the mid lift and dropped the trailer air out, you could quite possibly increase the drive axle weight to around 15 or more tons, now that would make a bloody big difference to whether you got up a slippery slope or not.
Word of warning, Stevieboy (having rechecked the other thread, i believe it was Captain Caveman who warned about the pick up ramps, apologies CC) did mention in a post to be careful doing this cos the trailer will be sticking up at the front, the chassis rails will get closer to the pick up ramps on the tractor, if you have them, so be wary on turns or rough ground.
SEVERE WARNING…remember also you will have raised the front of the trailer quite considerably, so be aware of your surroundings, buildings canopies bridges etc, might be an idea to have a measure up anyway to see what difference it makes to your lorry, in conditions causing you to make use of this the height increase might easily slip your mind.
Many thanks to Stevieboy308, i’ve learned something that will likely be very useful during the winter, though i suspect the offroad lads already knew all this.
and breathe 
hopefully someone with an idea what going on will turn up and explain it in terms even i can grasp.
