A trailer doesn't react to a tractor's backing up until 10 feet of travel

[bluemoonKY]

I am a trucker. I pull 53' dry van trailers with a big rig truck (a tractor). When a tractor-trailer backs straight backwards (not turning ) it is called straight line backing. Probably most people here know from backing boat trailers or other trailers at some point in their lives that when backing a trailer, if you turn the steering wheel to the left, it will make the rear of your trailer go to the right and if you turn steering wheel to the right, it will make the rear of the trailer go towards the left.

Both the trucking school i attended and the trucking company i now work for told me that when a tractor-trailer is doing straight line backing, if the truck driver turns the steering wheel to the left or the right, the trailer will not respond by going the opposite direction until the tractor has backed up around 10 feet. To me, this seems counterintuitive and also potentially false. The tractor is connected to the trailer at the fifth wheel of the tractor. The trailer has a cylindrical bolt hanging down from the front of the trailer called a kingpin. The fifth wheel of the tractor has locking jaws that lock around the kingpin. The connection between the fifth wheel and the kingpin is a rigid connection. To me, it seems like since the connection between the fifth wheel and the kingpin is a rigid connection, that should mean that the trailer will react to the driver's turning the steering wheel (during straight line backing) IMMEDIATELY. Maybe the trailer's reacting to the driver's turning the steering wheel might be too subtle to detect until the tractor has backed ten feet, but it seems to me that the trailer's reacting to the driver's turning the steering wheel should happen when the tractor has moved just one foot. The instructors at my truck driving school said that when a trucker is doing straight line backing, the trailer won't react to the driver's turning the steering wheel until the tractor has backed 10 feet b/c the circumference of the wheel on the tractor-trailer is ten feet. I don't see how the circumference of the wheels could determine when the trailer reacts to when the driver turns the steering wheel.

Are the instructors at my truck driving school and at my trucking company correct that the trailer will not react to the driver's turning the streering wheel until the tractor has backed 10 feet?

Please explain.

 

[jbriggs444]

You are correct. The instructors are blowing smoke.

The track of the trailer will not react significantly for a while because, as you well know, it takes some distance for the cab to move appreciably to the side, thereby changing the trailer's orientation and it then takes some distance for the trailer to move to the side as a result of its new (and still changing) orientation. The circumference of the wheels does not enter in. The same would apply if you replaced the wheels with a set of (incredibly sturdy) roller blades.

 

[bluemoonKY]

The track of the trailer will not react significantly for a while because, as you well know, it takes some distance for the cab to move appreciably to the side, thereby changing the trailer's orientation and it then takes some distance for the trailer to move to the side as a result of its new (and still changing) orientation.

I think the key word in your quote is "significantly". I think that when a trucker is straight line backing, the track of the trailer will already be reacting (in a negligible and undectable amount) to the driver's turning the steering wheel when the tractor has just backed a foot, but the track of the trailer will not react "significantly" when the truck has just backed up a foot.

The circumference of the wheels does not enter in. The same would apply if you replaced the wheels with a set of (incredibly sturdy) roller blades.

I agree. When my instructors first told me that, I didn't understand how the circumference of the wheels could affect when the trailer reacts to the tractor, but I did not necessarily think it was wrong. I had to keep paying attention to other things the instructors were saying, and I thought to myself: "I will think about it later." Then when I did take the time to think about it, I still didn't see how the circumference of the wheels would affect when the trailer reacts to the tractor. Now I think: How does the circumference of the wheels affect when the trailer reacts to the tractor? The answer is: It does not.

 

[berkeman]

One big difference between a boat trailer (or my motorcycle trailer) and an 18-wheel trailer is that the latter has its fixed wheels at the very back, not mid-trailer. That is a reason that the back of your trailer will not react as quickly as a trailer with fixed wheels mid-way back.
http://www.ronstoyshop.com/category_images/trailer_catalog/enclosed_cargo_trailers/6_wide_trailers/trailers_car_mate_enclosed_cargo_trailer_600.jpg

http://www.utilitopics.com/wp-content/uploads/Prime-Trailer-e1422390133880.jpg

 

[RonL]

A brush guard on front of a big rig a first time view for me

 

[sophiecentaur]

When my instructors first told me

I have had dealings with instructors, teaching parachute jumping, plumbing and scuba diving etc. etc.. They can be excellent at telling you what to do but that doesn't mean that their knowledge of the Science is enough to give valid reasons. I have heard an amazing amount of pseudo Science from guys with whom I would willingly trust my life. It's two entirely different disciplines.
The Army teaches 'by numbers' because that wins battles - and a good thing too. "You're not here to think, soldier!"

 

[OCR]

I don't see how the circumference of the wheels could determine when the trailer reacts to when the driver turns the steering wheel.

It's called "the ten foot rule"... and, due to "rear trailer swing", it comes into play more so when doing sharp or 90° backups....
Here's the full video...

Now!... let's see you back up a set of doubles ....

If parked in a straight line, a set of triples can usually be backed up until the last trailer starts to jacknife, which isn't very far... it's about like trying to push a chain... lol

 

[256bits]

One thing to point out here, hinted at but not explicitly mentioned, is that the 53 foot trailer doesn't react to the orientation of the steering wheels, but to the orientation of the tractor wrt the triailer. The tractor has to be orientated to the left to make the rear end of the trailer move left. How to do so - turn the steering to the right to swing the tractor front to the left.

The fifth wheel is located right above the axle of the tractor, so one doesn't get the same more immediate angling by turning the steering ( as one would get with a hitch trailer). About 10 feet movement backwards is about right for the trailer to be noticeably orientated differently - and the rear might be now only 2 to 3 inches off from the line it was on before - probably about a 2 to 3 degree orientation of the trialer, depending upon the turning radius of the tractor - not really all that much of a reaction. Backing up another ten feet, with the same cranking of the steering, swings the cab out more, and the effect becomes much more noticable.

Ten feet is about one rotation of the tires, in other words the circumference of the tires. What better way to remember for the new driver how the trailer will react, and organizing his distance, and off-centre to the dock than putting it all in those terms. KISS has a workable outcome here.

Are we so sure the instructors are not saying that - ie that it takes one rotation of the tire to make, for the first 10 feet, to make a noticable effect, and it is getting misconstrued instead into "radius of the tire".

Any proof in trucking literature that circumference of the tires affects backing up, is an industry-wide recognizable explanation. I don't see the whole industry completely falling hook line and sinker falling for that one.

 

[OCR]

A brush guard on front of a big rig a first time view for me

Really ?... interesting....

https://en.wikipedia.org/wiki/Bullbar

http://www.herd.com/gallery/default.aspx?cmd=reset

 

[256bits]

It's called "the ten foot rule"... and, due to "rear trailer swing", it comes into play more so when doing sharp or 90° backups....
Here's the full video...

Now!... let's see you back up a set of doubles ....

If parked in a straight line, a set of triples can usually be backed up until the last trailer starts to jacknife, which isn't very far... it's about like trying to push a chain... lol

Try a hitch trialer that also steers! Lots of fun. But you get used to it, so you don't end up bending the hitch and tow bar and other things. Especially at harvest time, when downtime means $1000's per hour or more. Came close though.

 

[RonL]

So now I have really embarrassed myself, that first picture is an over the road beauty, your picture made me remember my oilfield days, those pictures nudged my memory and that led me to remember "I actually own a 1966 Ford tandem axle truck with a brush guard" DUH! it has been a good weed killer for quite a few years used to have a cement mixer over the wheels

 

[OCR]

Especially at harvest time, when downtime means $1000's per hour or more.

Yup.....

 

[OCR]

"I actually own a 1966 Ford tandem axle truck with a brush guard"

This one, right ?

Lol, just kidding... pretty, though, isn't it....

 

[bluemoonKY]

One thing to point out here, hinted at but not explicitly mentioned, is that the 53 foot trailer doesn't react to the orientation of the steering wheels, but to the orientation of the tractor wrt the triailer.

That is true. On the first day that I ever tried alleydocking a tractor-trailer at the truck driving school I attended, I did not realize that the trailer does not react to the orientation of the steering wheels but to the orientation of the tractor with the trailer. I had the truck to myself, and I tried to alleydock into a parking spot for about an hour and a half without getting it into the spot. I mean, I was no closer to the parking spot after 90 minutes than after 5 minutes. Then I realized that the trailer reacts to the orientation of the tractor with the trailer. The way I thought of it is that when alleydocking (or doing any type of backing) , the trailer reacts to how the tractor "pushes" the trailer. Once I realized that, I could alleydock without any problems.

The fifth wheel is located right above the axle of the tractor, so one doesn't get the same more immediate angling by turning the steering ( as one would get with a hitch trailer).

Wrong. When backing, the trailer will immediately react to whatever way the driver turns the steering wheel. It's just that the reaction is too subtle for most people to notice until the tractor has backed 10 feet.

Ten feet is about one rotation of the tires, in other words the circumference of the tires. What better way to remember for the new driver how the trailer will react, and organizing his distance, and off-centre to the dock than putting it all in those terms...

Are we so sure the instructors are not saying that - ie that it takes one rotation of the tire to make, for the first 10 feet, to make a noticable effect, and it is getting misconstrued instead into "radius of the tire".

Any proof in trucking literature that circumference of the tires affects backing up, is an industry-wide recognizable explanation. I don't see the whole industry completely falling hook line and sinker falling for that one.

First of all, please review my original post on this thread. I never used the word radius in my original post.

My instructor said that because the tires are 10 feet in circumference, that means that it takes the tractor's backing 10 feet for the trailer to react. I don't think that the whole industry thinks that the tires' circumference is what determines how long the tractor has to back for the trailer to react. That's just what one instructor said.

Since both my trucking school and the trucking company I now work for both say the same fallacy about the trailer not reacting until the tractor backs 10 feet, I think that the fallacy of the trailer's not reacting for 10 feet might be an industry wide fallacy. The trucking school I attended and the trucking company I now work for are not affiliated with each other, so I doubt one of them got the fallacy from the other. This adds plausibility to the theory that the fallacy is industry wide.

 

[OCR]

Once I realized that, I could alleydock without any problems.

...

 

[RonL]

This one, right ?

View attachment 104881​

Lol, just kidding... pretty, though, isn't it....

Mine has the gas engine and not nearly as heavy duty, nor a sleeper cab as the one above.

 

[berkeman]

the trailer reacts to how the tractor "pushes" the trailer.

That's how I back my motorcycle trailer. Visualize how my steering wheel movements push my hitch, and visualizing me using my hand to move the hitch to turn the trailer. Works well for me.

I can't imagine how to try to back a double trailer.

 

[256bits]

First of all, please review my original post on this thread. I never used the word radius in my original post.

My instructor said that because the tires are 10 feet in circumference, that means that it takes the tractor's backing 10 feet for the trailer to react. I don't think that the whole industry thinks that the tires' circumference is what determines how long the tractor has to back for the trailer to react. That's just what one instructor said.

circumference = 2π radius

My instructor said that because the tires are 10 feet in circumference, that means that it takes the tractor's backing 10 feet for the trailer to react. I don't think that the whole industry thinks that the tires' circumference is what determines how long the tractor has to back for the trailer to react. That's just what one instructor said.

Since both my trucking school and the trucking company I now work for both say the same fallacy about the trailer not reacting until the tractor backs 10 feet, I think that the fallacy of the trailer's not reacting for 10 feet might be an industry wide fallacy. The trucking school I attended and the trucking company I now work for are not affiliated with each other, so I doubt one of them got the fallacy from the other. This adds plausibility to the theory that the fallacy is industry wide

The fallacy I was referring to, as your instructor seems to believe, is with the circumference of the tires being a factor.
Go for the 10 foot rule and you should be good.

 

[256bits]

That is true. On the first day that I ever tried alleydocking a tractor-trailer at the truck driving school I attended, I did not realize that the trailer does not react to the orientation of the steering wheels but to the orientation of the tractor with the trailer. I had the truck to myself, and I tried to alleydock into a parking spot for about an hour and a half without getting it into the spot. I mean, I was no closer to the parking spot after 90 minutes than after 5 minutes. Then I realized that the trailer reacts to the orientation of the tractor with the trailer. The way I thought of it is that when alleydocking (or doing any type of backing) , the trailer reacts to how the tractor "pushes" the trailer. Once I realized that, I could alleydock without any problems.

Kudos for you.

 

[DaveC426913]

That's how I back my motorcycle trailer. Visualize how my steering wheel movements push my hitch, and visualizing me using my hand to move the hitch to turn the trailer. Works well for me.

Backing a boat trailer, I put my hand on the bottom half of the steering wheel. The trailer's stern will move in the direction I move the wheel. Push steering wheel left, trailer stern goes to left. Push right, goes right.

Ths would work on a rig just as well.

 

[sophiecentaur]

Backing a boat trailer, I put my hand on the bottom half of the steering wheel. The trailer's stern will move in the direction I move the wheel. Push steering wheel left, trailer stern goes to left. Push right, goes right.

Ths would work on a rig just as well.

On the subject of boat trailers, where the wheelbase is probably shorter than the car, if you reverse for ten feet on full lock, you can be sure of a jackknife. What counts is the relative wheelbase of the tractor and the wheelbase of the trailer. If the pivot is forward of the rear wheels (typical of a large rig) the situation is very different and much easier to deal with (but you still need a lot of room).
Your system for holding the wheel at the bottom is along the lines of pointing the line of the tiller in the direction you want to go then steering a boat astern - or standing forward of the wheel and steering in the direction you want to go. It gets to be second nature - except if you stop and think about it!

 

[anorlunda]

Backing a boat trailer, I put my hand on the bottom half of the steering wheel. The trailer's stern will move in the direction I move the wheel. Push steering wheel left, trailer stern goes to left. Push right, goes right.

Ah, I like that. Instead of a wheel, treat it like a tiller. Since my sailboat steers with a tiller, I'm very used to that. Thanks. @DaveC426913

 

[DaveC426913]

Ah, I like that. Instead of a wheel, treat it like a tiller. Since my sailboat steers with a tiller, I'm very used to that. Thanks. @DaveC426913

Heh. Contrarily, I own the smallest sailboat possible that has a wheel. It was the #1 requirement of The Admiral - who never could get the hang of a tiller. (She doesn't drive either, so not used to a wheel, but easier than a tiller)

 

[bluemoonKY]

Backing a boat trailer, I put my hand on the bottom half of the steering wheel. The trailer's stern will move in the direction I move the wheel. Push steering wheel left, trailer stern goes to left. Push right, goes right.

This would work on a rig just as well.

Dave, please review the original post of this thread before you post any further on this thread. Your post is not germane. This is not a thread about how to back a trailer. This thread is specifically about whether or not a trailer reacts to the driver's turning the steering wheel until the tractor has backed 10 feet.

 

[bluemoonKY]

Go for the 10 foot rule and you should be good.

The 10 foot rule is bogus. The trailer will react to the driver's turning the steering wheel instantly when the tractor backs up.

 

[OCR]

The 10 foot rule is bogus.

The "10 foot rule" is absolutely not bogus... however, it might have nothing to do at all with backing up a semi trailer .... lol

The first reference I'd heard about it, beside you, was in the video... I got a chauffeur's license back in 1972, and "grandfathered" that to a Class A CDL, with all the endorsements, including HAZMAT, but not School Bus. I had to take all the written tests, and a Background Check through the Transportation Security Administration... you probably know about the Transportation Security Administration.....

And, as I stated...

due to "rear trailer swing", it comes into play more so when doing sharp or 90° backups...

Watch the video again, maybe.....

You're right, though, this statement doesn't seem to make sense to me.....

A trailer doesn't react to a tractor's backing up until 10 feet of travel...

BTW, did you notice that the tractor runs super singles on the drivers...?

 

[DaveC426913]

This thread is specifically about whether or not a trailer reacts to the driver's turning the steering wheel until the tractor has backed 10 feet.

Yes. Did you not get the answer you sought? Typically, once an answer has been found, forum discussions tend to diverge. If you feel the answer has not been adequately answered yet, ask for clarification, and the thread will stay on-topic.

 

[RonL]

Yes. Did you not get the answer you sought? Typically, once an answer has been found, forum discussions tend to diverge. If you feel the answer has not been adequately answered yet, ask for clarification, and the thread will stay on-topic.

I'm so thankful I stayed on topic

 

[jim hardy]

I think the key word in your quote is "significantly".

right on. I'd have said "perceptibly" but that's just finicky editing.

 

[bluemoonKY]

Dave, the only replies that addressed my question are posts #2 and #8. But i would like more people's opinions. Also, i would like for people to answer in a more clear, unequivocal and direct way.

 

[DaveC426913]

...the trailer will react to the driver's turning the steering wheel (during straight line backing) IMMEDIATELY. Maybe the trailer's reacting to the driver's turning the steering wheel might be too subtle to detect until the tractor has backed ten feet, but it seems to me that the trailer's reacting to the driver's turning the steering wheel should happen when the tractor has moved just one foot.
...
Are the instructors at my truck driving school and at my trucking company correct that the trailer will not react to the driver's turning the streering wheel until the tractor has backed 10 feet?

It is quite likely that the instructors are talking in practical terms. i.e. what is the minium a driver needs to know to take the correct action.Afterall, there's a lot to learn.

If drivers were told that - technically - it reacts right away, that could very likely lead them to expect a visible change right way, and - if they don't see it - they may over-correct.

 

[EnumaElish]

The 10 foot rule is bogus. The trailer will react to the driver's turning the steering wheel instantly when the tractor backs up.

Everyone I've consulted on this agree it's bogus. Railroad locomotives back up while pushing RR cars. Sometimes they do that on a straight patch, and sometimes to push the car(s) through a switch, at an angle. If this rule were true, there would have been RR lore about attached car(s) not reacting before the engine has backed up 10 feet. But AFAIK there's no such belief among the railroad folk. Not one that google can find anyway. So why do people keep repeating it? Could the 10-ft rule meant to be the distance before the trailer will jackknife (unless the driver corrects), rather than the distance for the trailer to react? E. g. a correction rule? Perhaps that's how it started, but over time its meaning and intent was obfuscated?

 

[sophiecentaur]

Railroad locomotives back up while pushing RR cars.

Once you involve rails in the situation, everything is totally different. The path followed is totally governed by the rails and there is no 'steering' involved. There are, of course, minimum radii for railroad curves but that is a different matter, I think.

 

[EnumaElish]

Once you involve rails in the situation, everything is totally different. The path followed is totally governed by the rails and there is no 'steering' involved. There are, of course, minimum radii for railroad curves but that is a different matter, I think.

I agree with you on steering. But I do not see why the action-reaction lag should be any different. Actually your observation is very helpful to nudge this thread in the right direction. If the 10-ft rule does not apply to RR engines and RR cars then the only explanation for it to apply to tractors and trailers ("TT") must be because of steering. If steering cannot explain the rule for TT then the rule must be bogus.

 

[sophiecentaur]

I agree with you on steering. But I do not see why the action-reaction lag should be any different. Actually your observation is very helpful to nudge this thread in the right direction. If the 10-ft rule does not apply to RR engines and RR cars then the only explanation for it to apply to tractors and trailers ("TT") must be because of steering. If steering cannot explain the rule for TT then the rule must be bogus.

As far as I can see, the rule is followed by most TT combinations because the other dimensions are much the same, not surprisingly because they are probably near optimal. Overhang, wheelbases and positions of axles (and even the limits of the tractor steering, probably) will be what governs the locus of all the wheels.

 

[256bits]

As far as I can see, the rule is followed by most TT combinations because the other dimensions are much the same, not surprisingly because they are probably near optimal. Overhang, wheelbases and positions of axles (and even the limits of the tractor steering, probably) will be what governs the locus of all the wheels.

Three types of tractors, each with its own version of the rule guidline ( for new drivers )
Sleeper - the longest tractor wheelbase - most dificult to back up with.
Regular - for day trips - medium whellbase - what most one will see on the road.
Shuttle - shortest wheelbase - easy connect diconnect - open view - used around yards to manipulate the trailers around - excessively productive compared to the other types.

 

[256bits]

Three types of tractors, each with its own version of the rule guidline ( for new drivers )
Sleeper - the longest tractor wheelbase - most dificult to back up with.
Regular - for day trips - medium whellbase - what most one will see on the road.
Shuttle - shortest wheelbase - easy connect diconnect - open view - used around yards to manipulate the trailers around - excessively productive compared to the other types.

PS. trailers. 53 foot.
Rear three axle and two axle.
Rear axle can be on a dolly that can be moved ( just do the release and push the trailer box back or forth on the locked rear axles ) from most rear to about 1/3 from the rear, depending upon weight distribution.
Dolley position will affect the "ten foot rule" and driver will have to adjust.

 

[EnumaElish]

As far as I can see, the rule is followed by most TT combinations

Dolley position will affect the "ten foot rule" and driver will have to adjust.

Are you all referring to a rule in the sense of a physics theorem, or as folklore regardless of what physics says about it?

 

[sophiecentaur]

a rule in the sense of a physics theorem,

This isn't 'Physics'. It's Maths (Geometry), at least to a first approximation. You would get similar results if you treat everything as 'idea' and with no slippage or drag. The patterns will be derived from combinations of cycloid and tractrix type curves.

 

[EnumaElish]

This isn't 'Physics'. It's Maths (Geometry), at least to a first approximation. You would get similar results if you treat everything as 'idea' and with no slippage or drag. The patterns will be derived from combinations of cycloid and tractrix type curves.

Great. Now read the OP. Either point to a proof (sketchy is okay) or abandon all pretense.

I'll go first. My railroad analogy was posted under the false presumption that the OP was about backing up. I've gone back and reviewed it. I realize that it's about a change of direction while backing up. So my RR analogy totally misses the point. Thanks for pointing that out.

 

[jim hardy]

The angle between tractor's axis and trailer's axis drives itself toward zero when moving forward
and away from zero when moving backward.

When backing , the rate of angle increase per foot of travel depends on the angle. At zero angle it's zero. At any other angle it increases , proportional to magnitude of angle.
Anything whose rate of change is proportional to its magnitude is suffering exponential growth.

When moving forward , the rate of angle decrease per foot of travel depends on the angle. At zero angle it's zero. At any other angle it decreases, proportional to magnitude of angle. That's exponential decay instead of growth.

A perfectly aligned tractor and trailer with angle = 0 would be able to back clear across the Seven Mile Bridge were it not for that dogleg.
.

Exponential growth begins imperceptibly.
So while it might take something like ten feet for the rate of change of angle to become perceptible, rest assured it started much earlier.
Forward motion is the opposite - angle approaches zero asymptotically.


I recently moved the axle of my 12 foot long utility trailer eight inches rearward for two reasons.
1) make it easier to back up. It was overly prone to jacknife , as all short trailers are. Look at the geometry above.
2) move axle behind center of gravity to stop divergent side to side oscillations on the highway.
That dramatically improved its "user friendliness" on both counts.

old jim

 

[sophiecentaur]

Great. Now read the OP. Either point to a proof (sketchy is okay) or abandon all pretense.

I am not after a "proof" because that would certainly be very complicated but the basic behaviour of back and front wheels on a car will follow the same sort of argument as is used in the derivation of the tractrix curve. (with modifications that make it more or less impossible for me).
The following is "sketchy" but I think it heads on the right direction. The behaviour of the tractor when backing up and turning is, I reckon, based on the tractrix curve - see this link and the animation half way down (pushing part). That curve shows what would happen if the front wheels were steered to follow a straight path backwards but when there has been a slight deviation (i.e. it chooses between right or left) It will produce a jackknife, eventually and the curvature increases rapidly towards that condition. But the driver will prevent this condition by chasing a better path. This involves keeping to the same point on a newly positioned tractrix with a different pair of exes. It seems that for all steered vehicles, the tractrix curves are dependent only on the wheelbase and the direction of the steering motion relative to the axis. he shorter the vehicle, the sooner it will turn by a specified angle. The long trailer must move back further than the tractor, to achieve a given angle and, of course, the pivot will always be on the opposite side of the axis from the tractor steered wheels. So the reasoning in the OP would seem to be correct when it says that the reverse steering for the trailer, is always in the other direction but much smaller with a long trailer. Looking at the animation, the deviation from straight is very little until the movement of the driven end is something like the length of the string / bar / wheelbase. At this point the trailer will not deviate by much (tractrix applies here too, I think) - just enough to be noticed by the driver. The lateral movement of the pivot divided by the trailer length would give you the angle
The ten foot 'rule' is obviously very crude but it was probably thought up when rigs became all of fairly similar proportions (related to a Standard Container, these days) and the resulting error is actually not very great.
I know it would never apply to the situation of a saloon car and a short, general purpose trailer that's used for trips to the local dump or for camping because the trailer length is about half the wheelbase of the vehicle. It will jackknife in about one metre of bad reversing.
Edit: The 10 ft rule is only approximate but it must relate to the wheelbase of the tractor (and they will all be pretty similar). Using a specific number of turn of the wheels may be a better rule because (I imagine) the bigger tractors will also have bigger wheels (?) so there will be some compensating factor doing it this way.

 

[EnumaElish]

I think the rule can be seen in the attached video, mainly between 1:46 and 1:48 and up to 1:52. At 1:46 the trailer is halfway jackknifed. As the tractor backs up, the trailer pretty much pivots at the same spot. At 1:49 it starts to move back. So my thinking is, an actual tractor would have moved about 10 feet between 1:46 and 1:49. Hence the "10-foot rule."

http://www.loveyourrv.com/back-fifth-wheel-trailer/

P.S. Had the trailer fully jackknifed with a 90-degree angle, no amount of backing up could have pushed it back; it would merely pivot on its wheels. I suppose in that case the applicable rule would be the "no good rule" instead of the "ten foot rule." But then, a 90-degree angle is probably not part of an optimal trajectory when backing up a trailer.

P.P.S. Just realized @OCR had already explained this. And with a real-life video. Minus above hilarity.

 

[jim hardy]

Can a Tesla do this ?

http://www.usatoday.com/story/money/cars/2015/05/21/ford-f-150-backup-assist/27705471/

 

[OCR]

But then, a 90-degree angle is probably not part of an optimal trajectory when backing up a trailer.

In certain circumstances a 90°, or even more, angle can be useful to get the tractor in a better position for making pull-ups, for instance... I've used the technique when forced to make a u-turn on narrow roads.

I have even unloaded our dozer, and "dozed" the back end of our lowboy into a better position... that might not work too good in an RV park, though... lol

Just a couple pictures of dozer on lowboy... I was in the Big Horns, heading home from a fire.

 

[sophiecentaur]

Shame there's only a 'like' available for the above post. It would be nice to put in a 'heart'.

 

[DaveC426913]

New Series: The Littlest Dozer. (spin off from The Littlest Hobo*)

Goes across country, town to town, doing good deeds and helpin' folk outta trouble.

​

* Shoot it's a Canadian show. You prolly won't get the reference.

 

[jim hardy]

"The difference between men and boys is the size of their toys."

I just got a case of dozer envy.

 

[OCR]

* Shoot it's a Canadian show. You prolly won't get the reference.

Lol... well, I did have to look that up...

But it's not a German Shepherd ...

It's a Deere ... you know ?

"Nothing Runs Like a Deere"​

... better get back on track (s) ... lol