Real silly question does the location of the 5th wheel and the pin on the trailer make a difference to how the combination reverses. As i am an agency driver i drive a lot of different units although the majority are mercs and differing trailers although they are all tri axels. I have noticed though that the position of the unit to the trailor can change quite dramaticaly sometimes the back of the unit is nearly touching the legs of the trailer other times there is a good 3 feet.
The issue comes when its time to reverse I did think it ws because i was getting cocky and therefor screwing up easier ones through not concentrating enough. but recently i have been getting some regular places/bays and sometimes i can do it straight off and other times it takes a dozen goes.
Yes it does, and it makes a difference going forwards around corners too, both to how much closer, or not, the trailer wheels are to the kerb, and to how far the outer front corner of the trailer swings and risks knocking over a gatepost. The length of the trailer also makes big difference, even those who consider themselves ‘experts’ have an issue if they haven’t had a short trailer behind them for a while. It is all about which axle the trailer is pivoting about and that changes according to ground conditions and slope.
There’s roughly 18" (i haven’t measured it) of movement on a slider, generally i’ve found the ideal position for correct weight distribution on the tractor is about the mid way point, which makes sense.
If you moved the slider from one extreme to the other you’ve in effect moved the trailer axles by the same amount, plus the pivot point on the tractor has moved.
All different trailer types maneuver differently just like tractor units, some tractors have a brilliant lock and fast steering some have less lock and require more turns of the steering wheel for the same effect, some trailers will have axles further forwward or back than others, any trailer with a lifting axle in operation will change things the most dramatically.
Its not just you we’re all the same, as Blue Estate has found doesn’t matter if you’ve been doing the job forever a different wagon or trailer type can leave you making a right pigs ear of the simplest of maneuvers.
You should see me attempt to reverse a container trl or triaxle curtain sider into a standard bay when i’ve been pulling tanks for months on end, looked like i passed me test yesterday
One regular delivery point one of their fridge artic combos had been left in front of the silos, as i’m a regular there and none of their drivers in for several hours they asked me to move it and put it on a bay with trailer wheel guards, 6 shunts later and its somewhere thereabouts
cooper1203:
Real silly question does the location of the 5th wheel and the pin on the trailer make a difference to how the combination reverses. As i am an agency driver i drive a lot of different units although the majority are mercs and differing trailers although they are all tri axels. I have noticed though that the position of the unit to the trailor can change quite dramaticaly sometimes the back of the unit is nearly touching the legs of the trailer other times there is a good 3 feet.
The issue comes when its time to reverse I did think it ws because i was getting cocky and therefor screwing up easier ones through not concentrating enough. but recently i have been getting some regular places/bays and sometimes i can do it straight off and other times it takes a dozen goes.
There’s a good chance your over length running 13.6’s with the fifth wheel back that far that you’ve 3’ of space
One other thing, and the vast majority of drivers do not do this.
When maneuvering with a 3 axle tractor press the weight transfer button, which removes the air pressure from the mid lift axle (some makes lift completely after a short period), no longer dragging that tyre around nor putting undue strain on the suspension plus cuts the tendency to wheelspin down to the minimum, you can feel how much easier the vehicle is to maneuver.
Juddian:
One other thing, and the vast majority of drivers do not do this.
When maneuvering with a 3 axle tractor press the weight transfer button, which removes the air pressure from the mid lift axle (some makes lift completely after a short period), no longer dragging that tyre around nor putting undue strain on the suspension plus cuts the tendency to wheelspin down to the minimum, you can feel how much easier the vehicle is to maneuver.
This is a good tip. I did it all the time when I had an Actros (if you’re heavy hit both buttons at the same time, it lifts the mid axle until you reach 30kmh).
The Daf which came after was a twin-steer, so lifting the mid didn’t make much difference.
Rule of thumb for a bogie drive prime mover is 6" forward of centre of the rear axle group and 2~3" forward of centre of a tri-axle.
Single drive prime movers are an uncommon, vocational spec here, I haven’t driven one for forty odd years, but any fiddling with the turntable position on a single drive will have greater impact upon weight distribution, than on a multi-axle suspension group.
I don’t know about mid lift units, as hardly anybody up here has them. Tag axles are the unit of choice in the North.
As far as the fifth wheel position is concerned, I try to have mine set so that when you weigh the outfit, loaded, on a dynamic weighbridge, the front and rear axles are bearing almost exactly the same weight. The lorry handles best when set up like this.
Old John:
I don’t know about mid lift units, as hardly anybody up here has them. Tag axles are the unit of choice in the North.
As far as the fifth wheel position is concerned, I try to have mine set so that when you weigh the outfit, loaded, on a dynamic weighbridge, the front and rear axles are bearing almost exactly the same weight. The lorry handles best when set up like this.
Mid lifts with large wheels are usually ok for weight distribution or rather you have more to play with so not likely to have an overloaded axle, far more critical to get the position right when you have small wheels on the mid, without looking at it i think my mid lift max is 5.5 tons which is higher than most makes, but i’ve seen some as low as 4.6 tons which can sail close to the wind on heavy work.
When i got a new MAN with slider i set about getting the slider in the right place for axle weights, what surprised most was the further you moved the slider back the more weight was imposed on the mid lift i’d expected it to be the other way round for some reason, idiot i am, after a few uses of the roll over axle weigher gradually inching the slider forward we’re there at just about the mid way point, no surprise that the vehicle handles noticeably better when the axle weights are where they should be.
Don’t see that many tag axles on tanker work, at least down south, i know of several in use but with some tank designs its the position of the landing legs that causes the issue due to the obvious extra long tractor chassis behind the fifth wheel of a tag unit.
I suspect the higher likelihood of bad weather tends to the preference for tag axles the further north the operator is based?
Simon mentioned a twin steer tractor in his post, i had a new TS Sed Ack in 1984 and a new TS Scania in 2006 and rated the handling of both as excellent with wet cornering far more stable and predictable than with a fixed mid axle, what happened to twin steers as you seldom see one now?
Juddian:
Simon mentioned a twin steer tractor in his post, i had a new TS Sed Ack in 1984 and a new TS Scania in 2006 and rated the handling of both as excellent with wet cornering far more stable and predictable than with a fixed mid axle, what happened to twin steers as you seldom see one now?
Still quite common on Dafs I think. Our entire fleet had them until we changed to MAN in 2015 (also changed to a different “logistics provider” who may well have spec’d them differently. I notice that the couple of 2015 plate CFs that we’ve temporarily hired in are also fitted with steering mid-lifts. I’d always assumed (probably incorrectly!) that it was the Daf way of doing things.
Apart from axle weights, look for risk of physical contact between unit and trailer too.
Don`t get the rear unit lights knocked off by the trailer legs.
Top of trailer can hit top of cab, or rubbing plate can hit catwalk, even if straight, on sharp inclines.
Closer is better for fuel economy, but there are limits.
Still quite common on Dafs I think. Our entire fleet had them until we changed to MAN in 2015 (also changed to a different “logistics provider” who may well have spec’d them differently. I notice that the couple of 2015 plate CFs that we’ve temporarily hired in are also fitted with steering mid-lifts. I’d always assumed (probably incorrectly!) that it was the Daf way of doing things.
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Its a good way of doing things in my humble, though there’s probably a weight penalty of some sort as well as even more moving parts to take into account if you have hydraulics/blowers and associated extra tanks etc to fit along the chassis.
Still quite common on Dafs I think. Our entire fleet had them until we changed to MAN in 2015 (also changed to a different “logistics provider” who may well have spec’d them differently. I notice that the couple of 2015 plate CFs that we’ve temporarily hired in are also fitted with steering mid-lifts. I’d always assumed (probably incorrectly!) that it was the Daf way of doing things.
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Its a good way of doing things in my humble, though there’s probably a weight penalty of some sort as well as even more moving parts to take into account if you have hydraulics/blowers and associated extra tanks etc to fit along the chassis.
I’ve not driven a twin steered tractor, but I had LWB 8 wheelers for many years, and found the directional stability to be beyond compare, so if i had a mid lift, then i would want a twin steer.
Interestingly, some manufacturers are now offering positively steered tag axle units. The advantages of manouverability and particularly traction when making right turns on a loose surface are very worth while, and people I’ve spoken to who have them are very pleased with their performance.
^^^ not to mention the vastly better tyre wear and associated lower suspension wear they must be enjoying.
Daf’s in particular have really small tyres on the small wheel mid lifts, on tight truns fuly loaded they reach all sorts of angles look like they’re going to be dragged off their rims.
I agree about the direction stability, i went from a Volvo FM with fixed but raisable small wheel mid lift to a Scania with full size twin steers (both modern design car transporters) worlds apart in stability handling and control, plus where the Volvo could suffer the tail wagging the dog syndrome sometimes severely the Scania didn’t budge.
I’ve not yet seen a small wheel mid lifter that steers, don’t know if anyone even offers it as an option, probably not as small wheels are all about weight saving for max weight work, but an added bonus of the small wheels is more room around the chassis for auxilliary tanks and any specialised equipment such as hydraulics/blowers.
The other good thing about lifting axles, on my present steed which is just coming up on 500k, still have over 70% of original pads on the lifter, in theory should make a million before reline on that axle.
Many years ago I drove a mid lift Scania 113 with a big single pot slurry tank, no baffles either. The first bend loaded was a moment. There was also the effects of 20T of water doing whatever it felt like. That created a few moments too This was before air suspension was a thing, it even had a hydraulic lifter.
A while later I had a twin steer ERF EC 14 (with Eaton Twinsplitter ). A twin steers cornering is day and night, compared to none steering mid lift or tag, very positive even on snow and ice.
I found the Actros on air wasn’t bad at all when driving loaded. No moments. Mind you I’d also gained another 20 years experience. Slow manoeuvring you can always lift the mid, even fully freighted, up to 30kmh.
Daf 106 twin steer compared to Merc Actros mid lift weight wise, I don’t think there’s much in it. Although the Daf only has a 350l tank, the Merc had a 550l. Both on standard sized wheels.
I was quite shocked to discover that the 16 reg Iveco Stralis we had on the fleet had hydraulically controlled steering on the mid lift. I had thought that was only allowed on agricultural vehicles, but it cannot be the case.
cav551:
I was quite shocked to discover that the 16 reg Iveco Stralis we had on the fleet had hydraulically controlled steering on the mid lift. I had thought that was only allowed on agricultural vehicles, but it cannot be the case.
Hydraulic steering systems have been common on, particularly, rigid trucks and buses with steering rear axles, for quite some years now.
Volvo had a system which had no outside power source, but worked by using a closed system in which oil was displaced by a ram, one end of which was attached to the drag link, and the other end to.the chassis. When the drag link travelled back and forward, the oil was transferred, through pipes, to a ram, one end of which was fixed to the track rod on the rear axle, and the other to the chassis. They worked quite well when young, but if they got air in, were awkward to bleed.
Later types now have a pressure generating pump, and as far as I know, the steering of the rear axle is controlled by electrical sensors which direct the flow of oil.
(If you look at Volvo tractors with single tyred tag axles, most if not all now, have axles with king pins and swivelling hubs, and on those without a steering system installed, which are the majority, the hubs are locked in the straight ahead position by rods fixed to the axle)
Years ago boss bought a s/h Axor that had been only used to move traction engine Having only been on rigids for years but had artic license was asked to take outfit up north load of fabricated steel. First spot of trouble was coming out of yard left turn unit would not turn quickly but did turn All was ok until Builth Wells come up steep gradient to T junction need to turn left would only go stright reverse back try again same again 3rd go stright again so used deep kerb to turn right problem 5th wheel too far back no weight on front axle
moment. There was also the effects of 20T of water doing whatever it felt like. That created a few 
This was before air suspension was a thing, it even had a hydraulic lifter.
). A twin steers cornering is day and night, compared to none steering mid lift or tag, very positive even on snow and ice.