I was sent out with an 18.65m trailer the other day. Went well enough once I worked out that there was a button to lock the rear steer axle for the purposes of reversing.
But how does the rear steer axle decide on the angle to steer at? I’m sure it isn’t taking the steering angle from the unit because that wouldn’t be useful. Does it calculate it based on the angle of the 5th wheel to the trailer?
granddaddylow:
I was sent out with an 18.65m trailer the other day. Went well enough once I worked out that there was a button to lock the rear steer axle for the purposes of reversing.But how does the rear steer axle decide on the angle to steer at? I’m sure it isn’t taking the steering angle from the unit because that wouldn’t be useful. Does it calculate it based on the angle of the 5th wheel to the trailer?
It is steered via the fifth wheel. The kingpin is fixed to a plate that spins in the neck, which is attached to either long bars or hydraulic rams, which steer the rear axle. There is a wedge behind the kingpin, which fits in the jaws of the fifth wheel, so when the fifth wheel turns relative to the trailer, so does the steering axle.
The bars tend to steer the whole rear axle, on a turn table, whilst the hydraulic system tends to steer the rear axle wheels, like the front steering of the truck.
There’s a couple of ways. There’s like wedge within the fifth wheel and when the unit turns in relation to the trailer it applies pressure via hydraulics to the rear steering axle. More turning = more pressure = greater steering response.
Same can also be used but by using rods instead of hydraulics.
You can also get passive rear steer, which don’t really steer they just drag along on a pivot and match up via road friction.
Our stepframe lowloader has a passive rear steer, it just goes with the flow and helps out.
There is a locking pin that drops down when the reversing lights come on otherwise it will snap round the wrong way and work against you.
If the wheels are not straight when you put it in reverse it will not lock. We have a switch to manually force the reverse lights, say you want to reverse in to the left but kick round to the right first, if you don’t think there is enough space to get the wheels straight before reversjng you switch it on to lock the steer so that as soon as you stop and reverse they are already locked.
If you lock it for reversing, then it’ll just be passive, basically it’s like a trolley wheel
granddaddylow:
I was sent out with an 18.65m trailer the other day. Went well enough once I worked out that there was a button to lock the rear steer axle for the purposes of reversing.But how does the rear steer axle decide on the angle to steer at? I’m sure it isn’t taking the steering angle from the unit because that wouldn’t be useful. Does it calculate it based on the angle of the 5th wheel to the trailer?
This is called a selftracking axle, makes it easier to go into tight spots, and for reversing you need to block the axle, sometimes there’s a switch on the dashboard for that, most of the times it’s switched to your reverve gear.
The most common system used on stepframe trailers used for STGO CAT 1 work, as it doesn’t require all that more maintenance and it saves on weight.
Hydraulic steering works as Toonsy said, there’s a wedge that goes into the fifth wheel and that’s coupled to a turntable, hydraulic connections attached to the axles and the axles can be steered seperataly by remote control. Great system, until there’s a leak in the system. Once you’re used to it, you’ll never want to go back to trailers with fixed axles.
A proper rear steer means that all the trailer axles counter steer to reduce cut in.
Most of the designs are just to support and track a long overhang behind a fixed axle/s and/or to prevent the ‘fight’ between fixed tandem or triaxle bogies in tight turns.Big difference.
Carryfast:
A proper rear steer means that all the trailer axles counter steer to reduce cut in.
No, it doesn’t. It’s called a “rear steer” because it’s just the rear axle steering.
Trailers where all the axles turn are described as “positive steer”.
(Source for last bit - Rikki from here. He pulls 6-axle versions.)
Lucy:
Carryfast:
A proper rear steer means that all the trailer axles counter steer to reduce cut in.No, it doesn’t. It’s called a “rear steer” because it’s just the rear axle steering.
Trailers where all the axles turn are described as “positive steer”.(Source for last bit - Rikki from here. He pulls 6-axle versions.)
The trailer described by the OP is fitted with a passive steer system. It self tracks, is not linked to the fifth wheel, and has no outside power involved in its operation. As he says, there is a locking device which can only be engaged when the wheels are in the straight ahead position, to permit the trailer to be driven successfully in reverse.
A trailer with positively steered axles may have one or more of its axles steered by either mechanical or hydraulic means, usually controlled from a turntable which is built into the trailer at the rubbing plate. On these systems, when articulation takes place between the vehicle and the trailer, there is displacement, either mechanical or hydraulic, which is transmitted to the rear turntable, causing it to steer the trailer from the rear. Tridec is probably the manufacturer of the most commonly used system. Muldoon, from Ireland, also produce a similar system, but theirs tend to be operated by a hydraulic displacement system.
The other system, which is more sophisticated and expensive, is Command Steering. This is usually only found on specialist low loader trailers, and those used for very long loads.
With a command system, the driver, or an assistant, can, by using an electro hydraulic system, change the steering angle of the trailer wheels, regardless of the relative angle of the tractor and trailer, and this can even be done when the outfit is stationary.
Lucy:
Carryfast:
A proper rear steer means that all the trailer axles counter steer to reduce cut in.No, it doesn’t. It’s called a “rear steer” because it’s just the rear axle steering.
Trailers where all the axles turn are described as “positive steer”.(Source for last bit - Rikki from here. He pulls 6-axle versions.)
Positive steer used to describe an axle which is doing nothing more than supporting and tracking a long overhang behind two fixed axles to reduce cut in at the expense of tail sweep.
As opposed to an all steering ( rear steer ) bogie which can actually create less cut in from a much longer trailer and distance from pin to axles measurement than than that.
Unless I’ve missed something.
Lucy:
Carryfast:
A proper rear steer means that all the trailer axles counter steer to reduce cut in.No, it doesn’t. It’s called a “rear steer” because it’s just the rear axle steering.
Trailers where all the axles turn are described as “positive steer”.(Source for last bit - Rikki from here. He pulls 6-axle versions.)
I think you’ll find the man who has probably never driven one knows far more than this so called ‘Riki’ who pulls supposedly six axle versions. Be gone with you fairy tale woman
switchlogic:
Lucy:
Carryfast:
A proper rear steer means that all the trailer axles counter steer to reduce cut in.No, it doesn’t. It’s called a “rear steer” because it’s just the rear axle steering.
Trailers where all the axles turn are described as “positive steer”.(Source for last bit - Rikki from here. He pulls 6-axle versions.)
I think you’ll find the man who has probably never driven one knows far more than this so called ‘Riki’ who pulls supposedly six axle versions. Be gone with you fairy tale woman
Don’t tell me you need to tell them that they don’t know what they’re talking about.
A rear steering trailer indeed.
Positive steer used to describe an axle which is doing nothing more than supporting and tracking a long overhang behind two fixed axles to reduce cut in at the expense of tail sweep.
As opposed to an all steering ( rear steer ) bogie which can actually create less cut in from a much longer trailer and distance from pin to axles measurement than than that.
Unless I’ve missed something.
muldoon.com/sidewinder-about.aspx
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You’re certainly a whizz on Google, but you don’t even begin to understand the information you have gleaned.
Therefore sir, I charge that this post consists principally, of Testicles
The ballast trailers Rik pulls have command steering as well - in fact, on bad days, they steer the trailer by hand themselves, from the driving seat, while also steering the unit. I did ask him how the hell they do that, and the answer was “slowly”. 
They definitely call them positive steer, though. shrugs
I’m Positive that CarryFast will Steer this thread to 10 pages long 
Terry T:
I’m Positive that CarryFast will Steer this thread to 10 pages long
Brilliant.
He could do with some rear steer, given the number of U turns he does.
Lucy:
The ballast trailers Rik pulls have command steering as well - in fact, on bad days, they steer the trailer by hand themselves, from the driving seat, while also steering the unit. I did ask him how the hell they do that, and the answer was “slowly”.They definitely call them positive steer, though. shrugs
You are not entirely wrong.
Most trailers which are equipped with Command Steering, are also fitted with positive steering.
However, not all positively steered trailers are fitted with Command Steering.
Carryfast:
Lucy:
Carryfast:
A proper rear steer means that all the trailer axles counter steer to reduce cut in.No, it doesn’t. It’s called a “rear steer” because it’s just the rear axle steering.
Trailers where all the axles turn are described as “positive steer”.(Source for last bit - Rikki from here. He pulls 6-axle versions.)
Positive steer used to describe an axle which is doing nothing more than supporting and tracking a long overhang behind two fixed axles to reduce cut in at the expense of tail sweep.
As opposed to an all steering ( rear steer ) bogie which can actually create less cut in from a much longer trailer and distance from pin to axles measurement than than that.
Unless I’ve missed something.
Too much to list.
Old John:
Lucy:
The ballast trailers Rik pulls have command steering as well - in fact, on bad days, they steer the trailer by hand themselves, from the driving seat, while also steering the unit. I did ask him how the hell they do that, and the answer was “slowly”.They definitely call them positive steer, though. shrugs
You are not entirely wrong.
Most trailers which are equipped with Command Steering, are also fitted with positive steering.
However, not all positively steered trailers are fitted with Command Steering.
That makes sense. Thanks John.
Lucy:
Old John:
Lucy:
The ballast trailers Rik pulls have command steering as well - in fact, on bad days, they steer the trailer by hand themselves, from the driving seat, while also steering the unit. I did ask him how the hell they do that, and the answer was “slowly”.They definitely call them positive steer, though. shrugs
You are not entirely wrong.
Most trailers which are equipped with Command Steering, are also fitted with positive steering.
However, not all positively steered trailers are fitted with Command Steering.That makes sense. Thanks John.
The fact is if drivers don’t understand the two entirely different concepts of a longer trailer but with proper ALL axle rear steer to reduce cut in, as opposed to a positive or passive rear steer AXLE, which just supports and tracks a massive overhang behind a fixed axle/axles and think that the latter will behave like the former you’ve got a big and dangerous problem.See previous tail sweep crash topic in which I was flamed as usual for trying to bring attention to the difference.