what are the dangers of having the majority of the load weight on the trailer axles (besides overloading the axles) and only having about 3 tonnes over the drive axles?
Presuming this is a genuine question.
There’s just so much wrong wth that sort of weight discrepancy.
A typical 3 axle tractor unit with mid lift raised with empty trailer attached puts about 4 tons weight onto the drive axle, if you were loaded and the lifter was down and you really only added 3 tons more to the drive axle, that axle is doing the driving of and commanding the stability of a 44 ton vehicle with only just over 7 tons or as little as 5 tons imposed on said axle depending on mid lift (itself depending on GVW, load imposed on tractor and whether the drive has control of mid lift), that alone should tell you all you need to know.
Those 3 trailer axles have a combined weight of 24 tons legally, and they are in a straight line and that’s where they want to stay, its the tractor that controls the direction that trailer goes in, on the open road it would feel awful like trying to control a shopping trolley you’ve piled high at the front with beers and filled the arse end up with bog rolls, the heavy end is in charge.
Wear grooves on motorways would throw you all over the place, very likely to lose control on a wet road, no traction turning corners but worse still taking bends at speed not enough drive axle traction so the trailer could easily push the tractor sideways, and anyone who’s had an oversteer slide with an artic on a wet road will tell you the forces at work take some getting your head around let alone attempting to control it.
Pulling away from junctions would hazardous, serious danger of becoming stuck on hills, braking hard could easily result in a jack knife even with all the anti lock systems modern vehicles have.
Worse still, if the load was far enough back the trailer could be attempting to lift the tractor unit, especially over road undulations, add some rain, slippery surface, wear grooves and a bend or two, plus the load being behind wants to make the trailer snake like a caravan and you have the perfect scenario for uncontrollable disaster.
If you drive a 44 tonner, a 3 axle midlift tractor and 3 axle trailer, an ideal weight combination would be in the order of 6+, 5, 10+ tons respectively on the tractor axles (variable depending on mid lift specs) and 7 tons on each trailer axle giving you 43 tons all up and all axles nicely within tolerance but with that all important drive axle having enough weight on to be the ideal of dog wagging the tail, not the tail (trailer) doing the wagging instead.
That’s exactly what I was looking for, thank you for the info
Pleasure, but i’m more than a little intrigued by the question.
I was loaded on friday with quite a bit more weight on the trailer axles then there was on the drives and had to rearrange the whole load, so being a new driver wanted to know what the dangers would be of taking a load like that out on the road.
Superb answer Juddian.
It’s so important that folks stick to the basic rules of loading. And that will avoid all sorts of mishaps.
But thanks for putting up an interesting question and thanks again to Juddian for saving my fingers!
Pete 
CillitBang:
I was loaded on friday with quite a bit more weight on the trailer axles then there was on the drives and had to rearrange the whole load, so being a new driver wanted to know what the dangers would be of taking a load like that out on the road.
Good for you, someone thinking about the dynamics involved and taking avoidance measures is good news. 
My pleasure Pete, and yes it was very good question.
Very good question, and an awesome answer very helpfull!
Very good post from Juddian.
It is actually covered in EU legislation, for international traffic anyway.
“The weight borne by the driving axle or driving axles of a vehicle or vehicle combination must not be less than 25 % of the total laden weight of the vehicle or vehicle combination, when used in international traffic”
eur-lex.europa.eu/legal-content … 3-20190814
Ive done a lot of groupage work and certainly that rule isnt always followed, however Ive never heard of anyone being prosecuted for being under weight on a drive axle, but it would be easy to imagine this happening if a vehicle is stuck halfway up a hill, wheels spinning because there isnt enough weight on the drive, or after an accident.
Thats interesting Franglais, i didn’t know that 25% rule from EU regs, sensible too.
With typical UK spec 6 axle 44 tonners, we can’t make 25% @ 44 tons, as i’m fairly sure without looking the max drive axle weight on mine is 11 or just over 11 tons.
Those with small mid lifts, usually specced on max weight operations like bulkers/tankers, you have to be careful about putting too much weight on the tractor unit, whilst its difficult to overload the drive and steer axles, those mid lifts can be as low as 4.5 tons max, and positioning of the fifth wheel becomes really important to not overload that little axle.
Our 3 axle UK spec tractors must be assumed to be more stable due to the extra axle though when its a non steering mid lift slippery really tight roundabout are often better taken by a swift unofficial dumping of the mid lift air to transfer some additional weight onto that drive axle, which also allows the steer tyres some extra grip to actually pull the outfit through the corner…remember newer drivers that 3 axle tractor if the extra axle is a non steer jobbie (the most common by far) the tractor like those 3 trailer axles has to be forced to take the corner because it prefers to go straight on, so in tight and slippery situations and pulling away from slippery junctions especially when turning at the same time, it can help to temporaily transfer the weight off the extra axle…ideally cancel the weight transfer soon as you’ve completed the turn but don’t worry too much about forgetting to re-inflate the mid lift suspension, when you get up to 20mph the vehicle will do it for you.
Maneuvering is another time to dump that mid lift air, helps a lot with turning, cuts down on both tyre and suspension wear, proof is my mid lifts have currently covered over 270k and (the one that didn’t get punctured) is roughly half worn, watch a DAF in particular if fitted with small mid lift wheels when maneuvering fully freighted, if the driver doesn’t dump the mid lift air those small wheels go to weird angles as the suspension gives, much kinder on any vehicle and it helps you to turn easily.
Get to know how all this works, if adn when we get snow you’ll need to know this, and its better to learn this stuff before you need it in poor conditions.
What i would advise any new driver, especially if you have a regular vehicle, try and use weighbridges at premises you visit regularly, particularly ideal if they have an axle weigher, you can always ask permission, if you weigh out somewhere ask the weighbridge chap if he’d mind if you just weighed the trailer axles separately before you leave (just to make sure you’re legal etc), most of them are decent enough and it’s very handy to know where you are re weights…more involved i know but if you have an unmanned weighbridge or a particularly decent weighbridge chap, so long as the bridge is level and not a raised sort, you can roughly weigh every tractor axle by putting one axle on at a time and noting the weights, then weigh the lot, then move forward and weigh the trailer axles, when on air unless there’s a fault in the suspension they don’t vary much more than 100kgs between the 3…there, get your pen and ■■■ packet and do the sums comparing with whats on the plate in the cab, and you know the weight of every axle within 200kgs by that method.
If you have a sliding fifth wheel, especially important if you have small mid lifts, you can use the above weighing method to determine the ideal position for that fifth wheel, you’ll also find when the weights are ideal the whole vehicle handles better on the road.
Running with a 2 axle tractor with a tri-axle (UK spec) trailer when I`ve a full uniform load, or a diminshing load, a light drive axle is normally not an issue!
UK trailers designed for 3+3 use have the axles just a little further back than an EU trailer designed for 2+3 use.
Only 30cm or so, but it is noticeable if two are side by side. Looking at distance from rear to back axle is easiest.
CillitBang:
… and only having about 3 tonnes over the drive axles?
The short answer from my experience is its horrible to drive.
I drive double deckers and sometimes the really tall pallets have to go on the neck, but that might be 2 tonnes if unlucky.
If you then have another say 20 tonnes spread down the rear part - it wheelspins at junctions & even on motorways, feels like driving on snow when wet on corners and those tramlines on the M6 near M56 play havoc with the steering.
Ultimately try not to butbif you do, assume you’ve got no steering and no braking. Drive it like an unbaffled tanker.