Flicking through a book of theory test questions and this is a question that caught my eye. Interested to see how experienced drivers would answer.
just asked me wife this and she came up with the same answer as me and she don’t drive trucks
Loaded at the rear, tail wagging the dog. You need the bulk of the weight on the drive axle.
I’II reveal their answer shortly but needless to say the reason it caught my eye is because I don’t agree it’s correct.
I am sure from my test it was unloaded. I disagree and have answered the more believable option - fully loaded as it will be pushing you.
If you lose traction on snow or ice and are fully loaded, that is going to be more likely to jack-knife than an empty trailer in my opinion.
Yes a loaded trailer pushes down harder but on ice it would surely make little difference?
DSA book. page 40 - Unladen.
However, applying real-world physics, I tend to agree with Harry Monk.
I’d have said loaded at the rear. Of course it also depends on the weight involved.
I don’t have actual experience of it happening but I’ve slid a heavy 20ft to the back of my skel before, done a turn and got stuck at about 45 degrees with just the drive axle spinning hopelessly because it had no weight on it at all.
The answer to the question (required answer) is unladen as there’s less weight on the drive axle. In the real world I would have to disagree with it. Although how many times have you been going round a wet roundabout when empty ad the drive axle slips out a little? Makes you wonder.
I would of thought you’d need a bit of weight (probably at the back) to lighten the drive axles further and create a bit of momentum to get the drive axles to break traction.
hiya …at one firm i worked at a driver had 3 drop off places. 10 tons of 45gallon drums for York,
two pallets (3ton)of bitumen in tins for Newcastle and 10 ton for Gateshead. he loaded all the drums
on the back,(first drop) then off up to Newcastle,(i said to him why not put the drums in the middle)
no notice was taken, on his way to Newcastle he caught a tractor up a bit quickly.
when he braked the load sensor told the unit he was fully loaded as he had plenty of weight on the
front of the trailer,that sent stacks of air to the brakes. the trailer had little weight on the wheels they
all they locked up and did nothing only slide down the tarmac…say no more the road was closed all
day, even the rubbing plate ripped off the chassis as the outfit jack knifed into the front of another
lorry coming the other way.spread the weight if you can.
yeah but no mention of ice, logic yes but who would load at rear no proper wagon driver would answer any other than fully loaded i think because loading at rear wouldnt be in the equation would it
It all depends on road conditions, an artic can jackknife in any of the above circumstances but is less likely with no weight on. We have all seen jackknifed trucks and not all of them have been empty or loaded, Jam your brakes on ( through no fault of your own ) in wet, or icy or snow covered roads and see what happens !
Yes, their answer is unloaded.
Loaded at the rear is most likely to induce a jacknife in any conditions though - either on a bend where traction is low or through sharp braking.
I would say it’s not only incorrect but also dangerously misleading as it kind of implies putting loads on the rear of trailers is ok or preferable to an unloaded trailer.
truckyboy:
It all depends on road conditions, an artic can jackknife in any of the above circumstances but is less likely with no weight on. We have all seen jackknifed trucks and not all of them have been empty or loaded, Jam your brakes on ( through no fault of your own ) in wet, or icy or snow covered roads and see what happens !
Have you tried it?
As long as the ABS is in good working order on both trailer and unit with no mismatch between unit and trailer braking force, you would be very unfortunate to jacknife regardless to how the vehicle is loaded on any road surface condition, that includes heavy braking on a road were the near side wheels are on compacted snow and off side on dry tarmac, the vehicle will stop in a straight line! Well as long as you don’t panic and try and steer around anything, then ESP would be needed to get out of trouble then.
Own Account Driver:
Yes, their answer is unloaded.Loaded at the rear is most likely to induce a jacknife in any conditions though - either on a bend where traction is low or through sharp braking.
I would say it’s not only incorrect but also dangerously misleading as it kind of implies putting loads on the rear of trailers is ok or preferable to an unloaded trailer.
The DSA manual has been written by a stuffed shirt who has never so much as sat in a truck, let alone driven one. Of course a tail-heavy artic is more likely to jack-knife than an empty artic, I really can’t see the point is wasting any more of my life trying to explain it.
Tarrman:
The answer to the question (required answer) is unladen as there’s less weight on the drive axle. In the real world I would have to disagree with it. Although how many times have you been going round a wet roundabout when empty ad the drive axle slips out a little? Makes you wonder.
That’s easy to control though, isn’t it!
I would of thought you’d need a bit of weight (probably at the back) to lighten the drive axles further and create a bit of momentum to get the drive axles to break traction.
Hiya…tractor jackknife or trailer jackknife there are two different things and two things to course them.
braking hard can make the trailer come round on you empty.(trailer jackknife)
braking hard with load towards the back of the trailer the unit can go round and smash into the trailer
pushing the unit backwards.(tractor jackknife)Stobarts seem to have tractor jackknifes don’t know why.
maybe unit is over braking…in the old days when we had drum brakes the trailer brakes would be out of
adjustment…not sure about these disc brakes…maybe could be seized. or load sensor not adjusted correctly.
you,d need to look at the situation.
John
3300John:
Hiya…tractor jackknife or trailer jackknife there are two different things and two things to course them.
braking hard can make the trailer come round on you empty.(trailer jackknife)
braking hard with load towards the back of the trailer the unit can go round and smash into the trailer
pushing the unit backwards.(tractor jackknife)Stobarts seem to have tractor jackknifes don’t know why.
maybe unit is over braking…in the old days when we had drum brakes the trailer brakes would be out of
adjustment…not sure about these disc brakes…maybe could be seized. or load sensor not adjusted correctly.
you,d need to look at the situation.
John
Don’t forget the cruise control induced jackknife, seen a few of those over the last few years!
Perhaps the DSA have confused jackknifing with trailer sliding, similar results but different causes!
Tazbug:
Perhaps the DSA have confused jackknifing with trailer sliding, similar results but different causes!
I think that’s a bit generous really.
There’s no scenario where a trailer loaded at the rear is preferable to any other loading option. They really ought to remove the question it’s dangerously misleading.