Can someone explain (or at least point me in the right direction where I can find the info) as to the for’s and againsts of command rear steer verses castor rear steer trailers?
Not multi steer axles, just std tri axle trailers with a front lift axle, and a steer system on the rear axle only.
As a OEM who build “normal” tri axle trailers, we are now being asked more and more to build rear steer combinations, but this is a new area for us and such have little knowledge.
In saying that, we have already built a command rear steer using the ES-VE system and also a castor steer using the BPW system.
But it would therefore be of great benefit to have a better understanding of the pros and cons etc.
All our trailers are Lawrence Davids with rear caster steers and front auto lifts and i think they are good at their job they seem to follow you better on r/abouts and T jcts better than a six on the ground tri axle anyway and they must save a fortune on tyre scrub wear ( so why did the gaffer get Merc Actros’s with non steering mid lifts then )
The only downside is you have to get them as straight as you can before engaging reverse or they wont lock and you end up crabbing ( i have used this to my advantage once or twice though and it gets you some strange looks ) So if your going in to a tight yard you need to get out and pull the locking button before you even think about manouvering it in
Also the comedy value of watching the face of a new driver as his trailer starts crabbing wildly towards the gaffers shiny new Mercedes is priceless
Reef:
The only downside is you have to get them as straight as you can before engaging reverse or they wont lock and you end up crabbing ( i have used this to my advantage once or twice though and it gets you some strange looks ) So if your going in to a tight yard you need to get out and pull the locking button before you even think about manouvering it in
I must admit to geeting myself into a rite pickle when I had to deliver the first one to the customer. I took a wrong turn and went into a industrial park, as soon as I turned into it I knew that it was not the right turn. But the road went around to the left and I could not see around the corner so I was not to keen in carrying on any further.
So I decided to reverse…yeah right!
Coz I could not get the dam thing in a straight line the rear steer would not lock out. As a result every time I went backwards I went sideways.
God, how frustrating was that
On the flip side I also delivered a command rear steer to a customer and reversing that is not the easiest thing in the world to be honest.
Plus, we have had our customer complaining about excessive tyre wear but only on the centre axle?
We have had it Lasaligned twice now and also checked each axle weight when it was fully loaded, and they were all near enough equal weights. Which is what you would expect with air suspension, but it was worth a check just in case.
We have also had the Technical Manager from ROR in to inspect it, he dropped a bombshell in that according to him command rear steers suffer from tyre wear on the centre axle Prehaps I am not used to the reversing a command rear steer trailer, but I have found reversing a std tri a lot more precise to be honest?
Ya big pair of wooses !! Them rear steers are easy, there’s nothing to them. Even the small ‘urban’ rear steers with twin axles arn’t that difficult, tight lock or no tight lock.
But your problem with middle axle tyre wear is it due to drivers going around with the front axle up?
I’m not sure what you mean to be honest when you say command and castor, i thought there was only one type. Malcolms have a lot of rear steers,i was under the impression because its what i was told by some one that the rear steer when traveling forward gives a smoother ride and as they carry a lot of glass including small jars for bottling etc it helped improve the percentage of loads being ‘shot’.
The short Urban trailers it gives you the sharpness on turning in a small area combined with the weight carrying benefits if twin axles?
Anyway, whats the physical differences between the two types?
Castor rear steers are exactly that Mike. Those are the ones you have to lock straight for reversing. They steer according to the leverage on the steering axle from the other two axles.
Commanded steer is the sort of thing you see on low loaders and the like, where all the axles steer to swing the trailer out in a turn.
Thinking about it, I’m not that surprised that the middle axle of a command rear steer scrubs.
On an ordinary tri-axle trailer, the turning centre of the trailer is more or less on the middle axle. If you have a lifting front axle, when its lifted the turning centre moves back to between the other two axles.
On a tri-axle trailer with castor rear steering, the turning centre is between the two front axles. If you lift the front axle, it moves back to the fixed axle. The castor effect simply adapts to the different leverage on it.
On a tri-axle trailer with command rear steer it has to be set up to suit one turning centre, it can’t then adjust itself. Obviously it’s going to be set up for running at full weight, with all axles down, so the turning centre is going to be between the two front axles. When you lift the front axle the turning centre will move but commanded steer will still steer the same for any given turn. So it’s going to steer against the fixed axle.
The only way I can see, to prevent the extra wear on the middle axle, is to have the steering axle lift instead of the front one. That way the turning centre of the trailer stays in the same place too, so it would presumably still meet C&U reg’s.
What I have noticed with Castor steer tri-axles is that the axle assemblies are invariably mounted further towards the rear than on a non-steering trailer. Whether this is for the benefit of of better weight distribution, I’m not sure, but in relation to another discussion, relating to rollovers, there is a possibility that mounting what must be in the region of three tonnes or so, half a metre or more, closer to the rear, would more effectively ‘anchor’ the trailer to a greater degree and make rollovers less common.
When I had the opportunity to drive the Denby Roadtrain, one of the topics was that the second trailer effectively ‘anchored’ the first trailer to the road and we therefore be virtually impossible to overturn.
At the C.V. show, on one of the stands, I think it was Krone, I spotted a Tri-axle with the leading and centre axle in conventional locations, whilst the trailing (steered) axle was half a metre or more further back than one would normally expect to see. I was told that this was a common arrangement for Scandinavia, although I can’t find any photograph showing this, in their product range.
Whilst Simon is correct in his analysis of the causes of excessive tyre wear, I can’t see any reason why, with a Command Steer’ system, it is not possible for the act of lifting the lead axle to automatically ‘re-map’ the angle of turn on the steer axle, although this may not be practicable having regard to Con&Use turning circles.
Ok, i’m with it now. Castor rear steers do not need to be locked for reversing though, even tight turns. All of the Malcolms lads never have a problem and i’ve never need to lock them myself. Same with the short twin axle trailers Tescos has. If you did lock them you wouldn’t get into tight places. If you are reasonably competent at reversing, half an hour or not even that having a practice in a yard will get you familiar with them. Just different but in no way hard.
Mike-C:
Ok, i’m with it now. Castor rear steers do not need to be locked for reversing though, even tight turns. All of the Malcolms lads never have a problem and i’ve never need to lock them myself. Same with the short twin axle trailers Tescos has. If you did lock them you wouldn’t get into tight places. If you are reasonably competent at reversing, half an hour or not even that having a practice in a yard will get you familiar with them. Just different but in no way hard.
Castor steer axles need to be locked because, otherwise they have a mind of their own.
Command steer axles steer (according to the command sent to the rams) whether going forward or reversing.
Need to be locked? You’re going on the long list of drivers who can’t reverse a trailer !!!
I only have a limited experience of castor steer axles and on the couple that I used, they automatically locked when you engaged reverse. However you did need the “steer” axle to be straight to do that. Not difficult (even at morrisons willand rdc)
Thanks guys, the text explaining the tyre scrub on the command rear steer was most interesting and answers a lot!
As for reversing without locking castor steer axle, I cannot see how you could do it without it being locked? Surely the trailer would have a mind of its own?
add me to that long list as well mike,
you’ve either been lucky or you’ve never reversed an unlocked castor type.
you can’t direct an unlocked one, it will turn against your lock and keep going on the same lock, the only way to straighten the wheels is to pull forward and start again.
you have no control over where it goes, you can’t correct it once it goes against you
biggusdickusgb:
you’ve either been lucky or you’ve never reversed an unlocked castor type.
you can’t direct an unlocked one, it will turn against your lock and keep going on the same lock, the only way to straighten the wheels is to pull forward and start again.
you have no control over where it goes, you can’t correct it once it goes against you
Thats exactly what I thought but dare not write it.
biggusdickusgb:
you’ve either been lucky or you’ve never reversed an unlocked castor type.
you can’t direct an unlocked one, it will turn against your lock and keep going on the same lock, the only way to straighten the wheels is to pull forward and start again.
you have no control over where it goes, you can’t correct it once it goes against you
Thats exactly what I thought but dare not write it.
I’m not sure what to say next here! If i get a chance to use one i’ll video it for ya. The ones i have used do not automatically lock. Yes, the rear trailer axle will be at an angle, and a tight one. But you just steer your tractor accordinglly. Its not a magic secret that i have, everyone does the same with them. I’m guessing you two guys are new or something? I well remember when i was new and seeing guys taking half an hour to get on a bay because the trailer rear axles ‘steered’? I watched them too and i was frightened to ever get one. But you shouldn’t put people off, they are not difficult at all. Just different.
)
and it gets you some strange looks 
) So if your going in to a tight yard you need to get out and pull the locking button before you even think about manouvering it in
Prehaps I am not used to the reversing a command rear steer trailer, but I have found reversing a std tri a lot more precise to be honest?
