Talk:Semi-trailer/Archive 1

???
I'm not sure how much can be added to this article? RfD and move its content to Wiktionary? Xiner 17:40, 4 October 2006 (UTC)
 * I separated Semi-trailer because people had commented variously at Talk:Semi-trailer truck that it needed a separate entry and that they wanted to add content to such, as some had at that talk page. Some of those comments are months old now, so who knows what will come of them, but that was the idea. ENeville 17:54, 4 October 2006 (UTC)

Trailer technology
In answer to all the above;- There are a great number of different types of semi-trailers, a lot of technology and a certain amount of history which needs to be added here but it takes takes time to do the research, gather the necessary illustrations and continue to write the article. If anyone beats me to it, be my guest. Apgeraint 05:07, 13 January 2007 (UTC)

Battery semi-trailer
"A battery propulsion semi-trailer is a semi-trailer that contains the batteries that are used to power an electric truck or bus." Has anyone ever really built a semitrailer equiped with this many batteries? I'm familiar with the concept of using a smaller one, but I've never seen pictures or heard discussion of one much bigger than a one or two axle thing that could be towed by a much lighter vehicle. If they have, surely it warrants expansion to cover how many batteries, the range, the load capacity, etc. like all the other electric vehicle articles. MrZaius talk  17:07, 13 March 2007 (UTC)

proposed merge from Turnpike Doubles
The article Turnpike Doubles should be merged somewhere, but I suspect either Semi-trailer truck or Road train may be a better target. Or maybe these three (four with Turnpike Doubles) articles need to be considered together and ensure the right information is in the right one, with proper cross-linking. A turnpike double sounds like a "toy" road train with short trailers and single-axle dollies. --Scott Davis Talk 02:08, 8 February 2007 (UTC)


 * Probably just ditch that page. The information is covered better in the North America section of Semi-trailer truck IMNSO.  A turnpike double is a very specific rig - two ~50' trailers.  The Turnpike Doubles page is fairly confused.Toiyabe 19:41, 8 February 2007 (UTC)
 * Agreed. Should we redirect that page over to Semi-trailer truck? —Cliffb 04:35, 9 February 2007 (UTC)
 * Agreed. What Toiabe said. Greg L (my talk) 01:19, 19 August 2007 (UTC)
 * Better to fix the link on Interstate 90 (and perhaps expand the text to contain an explanation) and just drop/prod it - if we were keeping the article it should be named Turnpike double anyway (lower-case 'D', singular instead of plural). --Scott Davis Talk 07:04, 9 February 2007 (UTC)

I wrote the article: "Turnpike Doubles". I agree it is covered, to some extent, in other articles. However, this [Turnpike Doubles] is not an international term. It is a slang term in the United States. It is important to note: that to Drop the "S" at the end of Double(s), would not properly represent the slang term. The colloquial term in the United States is, "Doubles" not "Double". If the article must be internationally ambiguous, then my definition of the USA slang is irrelevant. - Don Corman — Preceding unsigned comment added by 74.65.169.233 (talk) 16 June 2007


 * Would it be stupid to make a list of differently named road trains in the road train article, as to cover local and international terms for vehicle combinations with more than one (semi)trailer? G®iffen 11:25, 16 June 2007 (UTC)


 * Don - would one of these trucks be "a turnpike double", "a turnpike doubles", or "a Turnpike Doubles" (plural and case)? I'd also support merging the article and listing names in one of the other articles. --Scott Davis Talk 14:22, 16 June 2007 (UTC)

Scott- I'm not sure that a slang should be a separate article. The actual term used by regulators/operators in USA is "Tandem Trailer Operation" (TTO) A driver might be overheard to say, "I'm hauling doubles to New Jersey tonight", or,"I'm going to be pulling Triples to Chicago", etc. I question the relevancy of my article as more than a footnote, to clarify a colloquial term. - Don


 * -)Good idea, they should be on the same page. When adding things dont forget about other countries. I am an Australian and we have similar trucks to what is described. One being the 'Road Train' or 'Triple' where trailers are coupled together with dolly's, also there is a 'B Double' where a smaller body trailer (normally 40' odd length with a 24' loadable body {ie. flat top or tautliner}) with a turntable fitted onto the chassis couples to the next trailer, which also can be configured into a 'B Triple' or 'AB Triple'. As a general rule now the smaller body trailer is called an 'A' trailer and the normal 45' trailer is called a 'B' trailer.- Wade from down under.  —Preceding unsigned comment added by 122.148.71.147 (talk) 11:39, August 30, 2007 (UTC)

Definition of Semi-trailer—comments please
In both this article, Semi-trailer, and the Trailer (vehicle) article, a semi-trailer is defined as a trailer without a front axle. This definitions does not specify the semi-trailer belongs a truck. Most trailers, including small trailers which are commonly towed by smaller vehicles with a tow hitch and are not part of a truck, do not have a front axle. The smaller trailers have one or possibly two axles with wheels in the middle or middle-to-back of the trailer to support the weight of the trailer, but their attachment to the towing vehicle keeps them level. However, both this article and the Semi-trailer section of Trailer (vehicle) are written as if they are only covering semi-trailers for full-size semi-trailer trucks.

Now the question is: 1. Is the definition correct ? Do these article/section need to be expanded to cover additionally small trailers without front axles (not part of trucks)? ... or 2. Should the definition be changed to:
 * A semi-trailer is a trailer without a front axle in a semi-trailer truck.

I am presently leaning towards the latter (changing the definition as in 2.). Before I make the definition change in the two articles, I will wait at least a week for feedback comments. H Padleckas 03:14, 13 July 2007 (UTC)


 * No, I don't think the definition is inadequate. It is general, covering a light trailer on a hitch behind a SUV, as well as heavy freight rigs.  What is inadequate is the article, which discusses only equipment appropriate to highway freight operations.  It needs a paragraph or even a mere sentence alluding to lightweight semitrailers.  Semi-trailer truck doesn't need that sentence, since it is more obviously restricted to heavy haulage.  Jim.henderson 05:08, 13 July 2007 (UTC)

I am the person responsible for writing this definition after having compared various driving manuals from the U.K., U.S.A., Canada and France. Semi is a French or Latin word meaning half, so semi-trailer means half-trailer. In other words, not a full trailer. A full trailer is one that's towed behind a vehicle and rolls along on its own wheels, whereas a semi-trailer has an axle (or axles) at the rear but none at the front since its front end rests on top of the tractive vehicle which supports a considerable proportion of its weight. The following definition, which is in three parts, is perfectly correct. Any trailer which fits the following definition is a semi-trailer irrespective of its size, weight or type of tractive vehicle. 1. "A semi-trailer is a trailer without a front axle." This is the very basic definition and '''2. "A large proportion of its weight is supported either by a road tractor or by a detachable front axle assembly known as a dolly."''' is a necessary extension of this definition explaining that since a semi-trailer has no front axle it needs to be supported at the front. This basic definition distinguishes a semi-trailer from a full trailer which is entirely (or mostly) supported by its own axles. Further explanation is then required, namely:- '''3. "A semi-trailer is normally equipped with legs which can be lowered to support it when it is uncoupled."''' The word "normally" is included here since a few semi-trailers don't have legs and need to be supported by other means e.g. blocks of wood when uncoupled. Apgeraint 18:59, 3 November 2007 (UTC)
 * I'd suggest that these need to be clarified a little more:
 * "A semi-trailer is a trailer without a front axle group, and with its rear axle group well behind the centre of the trailer." This distinguishes it from a trailer with a single axle group near centre.
 * "A large proportion of its weight is supported on top of either a road tractor, the rear of another trailer or a detachable front axle assembly known as a dolly." I'm not entirely happy with the word "large" here, as it implies too much to me. I've added the rear of another trailer to cover B-doubles and the like.  I've added that it is carried on top.  Otherwise, a trailer which has its single axle group located towards the rear and connects to a hitch ("tagalong") would fit the definition.  The wording still isn't ideal because a dolly is, by definition, another trailer, too.
 * "A semi-trailer is often equipped with legs which can be lowered to support it when it is uncoupled." I would much prefer the word "often" here to "normally".
 * I'd like to point out that some semi trailers are bolted to the prime mover via a ballrace and rocker feet instead of a quick-release turntable, and such trailers are never fitted with landing legs. There are many such exceptions, and our definition needs to be vague enough to cover them but specific enough to not include other types of trailer. --Athol Mullen 23:45, 3 November 2007 (UTC)

Here are my observations:- 1. A semi trailer is a trailer without a front axle: period. An axle group means two or more axles, so a trailer without a front axle group could still have one front axle so it wouldn't be a semi-trailer, would it? 1b, The rear axle group is not always well behind the centre of the trailer. Look at those in Canada and Michigan for example. Some have a group of up to 6 axles begining immediately behind the trailer legs. At least one axle is in front of the centre of the trailer. 2. The thing that separates the definition of a semi-trailer from that of a full trailer with an axle group near the centre therefore, is the fact that a large proportion of its weight is supported by the tractor or a dolly. You are right however to include that it may also be supported by the rear end of another trailer. I'd like to give a percentage figure on the proportion of weight supported by the tractor but since this varies from country to country and since Wikipedia is inernational this is not possible within the definition. Could be up to 40% though. The proportion is therefore quite large. 3. To say that a semi-trailer is "often" equiped with legs is not really correct since there are very few which are not equiped with legs. Count them and see! The word "often" suggests a smaller proportion, whereas the word "most" means a much greater proportion. Incidentally any trailer which is permanently or semi-permanently attached to tractor is more likely to be known as an "articulated vehicle" and any trailer permanently or semi-permanently attached to another trailer would be known as a "combination trailer". Apgeraint 12:31, 4 November 2007 (UTC)

After having read and replied to your comments it was necessary for me to add the following whilst keeping the definition as clear and unambiguous as possible:- "Some semi-trailers are fitted with a fifth wheel coupling at the tail end so that an additional semi-trailer can be towed. See B-Train." Apgeraint 13:24, 4 November 2007 (UTC)

(edit conflict)
 * If you haven't looked at my user page, I'd encourage you to do so before you respond.


 * From the Australian Design Rules definitions (based on UN-ECE regs):

Axle group - either a Single Axle, Tandem Axle Group, Triaxle Group, or Close Coupled Axle Group.
 * A rear axle group does not in any way imply that there is a front axle or front axle group. For axles to be considered to be a group, there are limits on how far apart they can be. An axle at each end of the trailer would be either considered to be 2 axle groups or a "non-complying axle group" (ie illegal). This is common to both US-FMVSS based regs and UN-ECE regs (and derivatives thereof).


 * I agree that the first one needs to be clarified a little (I considered it implicit but to a non-technical person, perhaps it isn't):
 * "A semi-trailer is a trailer without a front axle group, and with the centre of its rear axle group well behind the centre of the trailer."


 * I've seen various trailer configurations that would put anywhere between about 25% and 60% of the trailer mass onto the towing vehicle. I very nearly suggested something along the lines of typically in the order of 40% of the trailer mass when I was composing my proposed definitions earlier, but removed it because it is too much of an arbitrary figure. My concern with the word large is that it might be interpreted as being "most" or "greater than 50%", but if other editors agree with the use of that word I'm not going to argue the point.


 * Your comments on "articulated vehicle" and "combination trailer" are obviously a regional variation. In Australia, any truck and trailer combination that incorporates one or more semi trailers is considered to be an "articulated vehicle" whether they are separable or not, and the term "combination trailer" doesn't exist here. A dog trailer (defined as a trailer that is built as a permanently joined combination of semi and dolly) is registered as one trailer. All other combinations are registered as separate vehicles, even if they are bolted together and are inseparable. This also appears to be common to the UN-ECE regulations, which covers most of the world outside the USA.


 * The frequency with which trailers are or are not equipped with landing legs is also likely to vary significantly on a regional basis but I'm not going to argue that point.


 * On your last point, I'd point out that some semi trailers have a ringfeder or similar tow coupling hitch at the rear rather than a fifth wheel coupling on top. The tow coupling is then used to tow a dog trailer or a convertor dolly (aka road train dolly) with another semi behind that. --Athol Mullen 14:20, 4 November 2007 (UTC)

I heard the term 'combination trailer' circa 1980. It was a bureaucratic neologism and now it seems that it fell out of use.

The word 'articulated' simply means 'connected by joints' so any vehicle and trailer combination is an articulated vehicle. The Australian definition is correct. Here in France too we use the term véhicule articulé in the same way. You are right to assume that there are regional variations for in the UK only semi-trailer trucks and "bendy" buses are considered to be articulated vehicles and in the USA the term 'articulated vehicle' doesn't even refer to trucks. Wording these articles is very difficult in order to satisfy everyone.

As far as the definition of a semi-trailer is concerned: I wrote it in in simple language so that even a layman can understand and in layman's terms 'axle group' means 'a set of axles close together'. Your extract from the Australian Design Rules definitions confirms this. They simply show that for the purpose of the Design Rules a single axle is considered as an axle group. As you can see the word "group" has not been included after the words "single axle". Apgeraint 20:57, 5 November 2007 (UTC)

Low-loader
There is no mention of Low-loader which may be a UK-only term. I think the US equivalents are Lowboy and Drop-deck trailer but what is the difference between these two? Biscuittin (talk) 08:12, 6 June 2008 (UTC)

Marathon dentist
There are numerous safety issues besides jacknifing, not least the risk of cars being wrecked when they hit the sides or rear of a typical curtain-side trailer. Europe introduced reflective tape to make trailers easier to see; it isn't mentioned. The U.S. mandates underride protectors which are supposed to prevent "submarining' (they are completely useless, because they're rigid & will tend to take the top off a car, instead); this isn't mentioned, either. (Unfortunately, my source was a newscast...) If somebody can add...?  TREKphiler   any time you're ready, Uhura  01:09 & 01:23, 27 November 2009 (UTC)

Material challenged
"Since a semi-trailer rests on top of a tractor it has a higher centre of gravity which makes it less stable than a rigid vehicle"

Being a professional truck driver, I strongly object against this line. A fully laden tractor-trailer is much more stable than a rigid vehicle, due to its length. Putting "citation needed" for the time being. However, any users should note that this is not true in real life. Either a citation from a trusted and verifiable source must be placed, or I will personally delete this line. --lasombra bg (talk) 16:34, 11 February 2010 (UTC)
 * Do you argue a trailer is as stable as a rigid of equal length? I doubt that.  TREKphiler   any time you're ready, Uhura  16:50, 11 February 2010 (UTC)

A rigid truck at its maximum is 4 meters high and 8 meters long (just my driver's training, I may be able to provide a link later). An articulated truck (tractor-semi-trailer) is 15.5 meters long. These dimensions may be somewhat greater in U.S. and definitely greater in Australia. As a whole, a semi-trailer is more stable than a rigid truck of the same height due to its greater length. Once again, I'd like to underscore that it's just my personal experience and professional training. Lacking sources other than my personal experience, I don't want to change the line in question, as to avoid an edit war. I feel, however, that readers must be cautioned that this statement is dubious and in need of reliable sources. —Preceding unsigned comment added by Lasombra bg (talk • contribs) 21:17, 11 February 2010 (UTC)

I agree that the statement is poorly worded, but I don't know how to go about fixing it without making it a muddy mess. Lasombra, if I read your comment correctly you are asserting longitudinal (direction of travel) stability, but I believe the statement is meant to apply to transverse (perpendicular to travel) stability. As an example, a semi box trailer has all the weight above the fifth wheel height, but the box on a U-Haul type truck is lower because it doesn't include the coupler height. (Yes, I know they use smaller tires too.) The underlying logic of "High CG = bad" is sound, but it's too late for me to even attempt making a revision that it both clear and precise, especially trying to account for lowboys or drop box trailers like the kind used for racing haulers. Jelloman (talk) 04:43, 16 March 2010 (UTC)


 * Have a look now. This doesn't cover all cases, which would need citation anyhow, but IMO better addresses the hi-CG issue.  TREKphiler   any time you're ready, Uhura  09:13, 16 March 2010 (UTC)

An attempt at defining semi-trailer from first principles
I'm surprised that a robust discussion of the meaning of the term 'semi-trailer' has only indirectly touched on the central issue of why a certain type of trailer is considered to be in some way a 'semi' type, in comparison with other trailers that are considered to be simply 'trailers'. The obvious implication is that normal trailers are more proper in some way—that they fulfil, to a greater extent than a semi-trailer, some fundamental attribute of a trailer. If we hope to define the term 'semi', shouldn't we try to explain it, rather than simply listing the features now to be found on semi-trailers? I think the design features follow from the solution to the engineering design problem, not the other way around. It's the design solution, considered as a whole, which supplies the most complete definition of the solution—in this case, of the semi-trailer.

I agree that the question of definition is related to the fact—which has been mentioned but not explored—that some important fraction of the weight of a semi-trailer is borne by the truck. (I hope we all accept that various names are used for the towing vehicle.) Well, these things are related, but not simply equivalent. It may be a reasonable first step to state that the semi-trailer lacks a front axle, but this statement is surprisingly unclear in itself and therefore arguably inaccurate. (Yes, that's possibly a strange claim for me to make, but bear with me!) It skirts the main issue and does not help us create a solid definition. Even if we think we are clear about what it means to say that the trailer does not have a front axle (and I argue that it is not as simple as it sounds), should that really be accepted as enough to build a definition on? I would say not; that such a definition is 'necessary but not sufficient' (to use terminology that is more typical of mathematical logic than engineering).

Unfortunately, when attempting to standardise terminology, we often mistakenly seek phrasing that will deliver unequivocal definition purely through instrinsic meaning of words alone. This is misguided. The only path to shared understanding and agreement on terminology (and issues in communication generally) is to ensure that the questions of context and intent are never ignored. Yes, that means more work; yes, it may annoy some people, or even many. But look around you, right here on these pages. The results speak for themselves—ignore context and intent, and no lasting agreement will be reached! This means two things: That we accept that words inconveniently mean different things under different circumstances (even in science); and that we are forced to continually question and re-evaluate the intent of words that are spoken.

If somebody asks what we mean by the trailer not having a front axle, of course we could point out that a semi-trailer clearly has no integral front axle—ie, no front axle built in. But why is that, what does it even mean, and why should that earn the trailer the mysterious label 'semi'? As far as I can see, none of that has been firmly established in the discussion so far. As others have mentioned, there is another related fact to consider: That some portion of the trailer weight is borne by the axles of the towing vehicle. But how exactly are we to explain this (ie, how and why does this design work?), and what implications are there?

If we consider the basic design problem, we see that, for any configuration in heavy haulage, we must arrange for some fraction of the load to be carried by the driving wheels, wherever they occur in the final design. If we fail this requirement, then we encounter an upper load limit, due to loss of traction. That is, we can carry greater loads if we use the load to assist in the creation of traction by loading the driving wheels. For a heavy rigid configuration, this is (in principle at least) straightforward. The centre of gravity of the load occurs somewhere not too far from the driving axles, and we have satisfied at least our design requirements for traction. Once we step into the realm of truck and trailer, we see two choices:


 * 1. attach a trailer to a sufficiently-loaded truck—ie, a truck which itself carries a load in addition to the load in the trailer;
 * 2. use a truck that does not itself carry any load, and attach a trailer to it, which carries the entire load.

We see both of these options used in industry. A heavy rigid tipper truck often tows a trailer, where both the truck and trailer each carry a load—this allows a large load to be carried, while satisfying traction requirements. Alternatively, a separate powerplant, in the form of a prime mover or tractor truck, tows a semi-trailer. The truck itself provides weight through its driving axles that is insufficient to satisfy the traction requirements imposed by a large trailer. Therefore, the prime mover—by design—bears some fraction of the trailer's weight, to enable large traction forces to be generated, allowing higher load limits.

Now, thinking again about the design problem, we see that if we are to have such a configuration, where the truck is to carry some of the trailer load over the driving wheels, then we must locate the point of attachment in a sensible place. For stability, it makes sense to locate the trailer attachment forward of the rear-most axle of the tractor. Now we have an arrangement that works differently to a more separate truck-and-trailer configuration (eg, tipper and trailer). With the semi-trailer coupled to the truck, the rear axle(s) of the prime mover act as the front axle(s) of the trailer. In fact, this is the only major weight-bearing function that the rear truck axles perform, since the weight they bear without the trailer coupled is small in comparison.

There is another important difference in the geometry of this configuration: The trailer no longer trails fully behind the tractor. It is partially supported, and fully towed from an attachment point that is forward of the rear-most load-bearing axle of the towing vehicle, and therefore is considered a semi-trailer. As any driver will tell you, this change in geometry is responsible for characteristics in handling that are distinct from those of a rigid truck and trailer. In terms of weight distribution, a semi-trailer coupled to a prime mover behaves more like a combined articulated vehicle, than a truck with a separate trailer hitched to it. In an effort to recognise the characteristic design and handling of a semi-trailer configuration, this arrangement is often called a combination—a term that is used to clarify legal definitions and licensing requirements. A tractor truck with a single semi-trailer may be defined as a heavy combination, as opposed to a configuration with multiple semi-trailers—a multiple combination, which by nature, already subsumes the heavy combination.

So, semi-trailers are called that because that is exactly what they are—yes, they are full-sized, but do not fully trail. The designation 'semi' refers to function and geometry, and persists (ie, continues to be considered a useful term) because of operating characteristics that are inherent in the basic design. Aboctok (talk) 23:48, 22 May 2010 (UTC)