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Extra Axle

Reversing the dificulty inherent in reversing.
  (+8, -6)
(+8, -6)
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Pulling a trailer is no great chore, you simply attach it to your car and drive (looking occasionally into your mirrors to make sure it's still there) but reversing - or pushing - a trailer, when attached to your vehicle is a more difficult matter.

You twist in your driver's seat, turning your wheel to the right, and having the back-end of your car turning towards the left - only now your trailer is veering sharply off to the right!

Whichever way you turn, the trailer will head in a direction counter to the one you hoped it would.

The solution, of course, is to add a secondary trailer between the car and the 'real' trailer. This secondary one has an axle with wheels, but is otherwise very small, its only purpose being to add another pivot point to the system and in doing so, reverse the counter-intuitive nature of backing up a regular trailer.

zen_tom, Aug 07 2006

Some Diagrams http://www.bimmerbo...riginal/Trailer.JPG
To help in visualizing. [jhomrighaus, Aug 08 2006]

[link]






       //add another pivot point to the system and in doing so, reverse the counter-intuitive nature of backing up a regular trailer.//   

       And make the job of manuvering a trailer infinetly more difficult than it already is. Though this sounds great on paper it is really quite easy to back a conventional trailer and adding an extra pivot makes the job damn near impossible to do. As a Class A CDL holder I have some experience with this.   

       BONE.
jhomrighaus, Aug 07 2006
  

       [angel] oops - sorry!   

       //You twist in your driver's seat, turning your wheel to the right, and having the back-end of your car turning towards the left//   

       That is to say, right-hand down, reverse, and the car will rotate, around its vertical axis, to the left, (while your trailer will rotate about its vertical axis, to the right)
zen_tom, Aug 07 2006
  

       Drive backwards whilst looking in the mirrors?
Dub, Aug 08 2006
  

       It's still counter intuitive, whether you look in the mirror, or have had the extensive training required to qualify for your CDL/HGV license.   

       An extra axle would cause the trailer in your mirror to follow the natural reversing line of your car, rather than acting counter to that line.   

       Larger trailers (such as you might find behind CDL and HGV drivers) benefit less from this idea because of their size, visibility, and greater arc of movement provided by the average truck-trailer connection compared to the more restrictive small trailer hookup available to cars with an attached blobby thing at the back (what are those things called?)
zen_tom, Aug 08 2006
  

       A little trick that really helps is to position your hand on the bottom of the steering wheel while backing, then just move your hand in the direction the trailer should go. Its really very intuitive then.
jhomrighaus, Aug 08 2006
  

       //That is to say, right-hand down, reverse, and the car will rotate, around its vertical axis, to the left//

Mine doesn't. Right hand down - ie, turning the steering wheel clockwise - turns the front wheels to the right. If I'm going forwards, the car turns to the right, away from the large brick wall on the left hand side of the car; if I'm going backwards, the car also turns to the right, also away from that wall.
angel, Aug 08 2006
  

       [jhomrighaus] the fact that you hold a class A CDL and can doubtless trailer with the greatest of ease does not negate the value of this idea for a trailering novice. I can follow your tip and [tom]'s logic, and I can't see how a device that turns the trailer into an extension of the back of the towing vehicle in behavioural terms can possibly complicate things . [+]

[angel] I think [tom] is taking his perspective from the front of the car which will turn in an anti-clockwise direction when you apply steering in a clockwise direction and move backwards.
DocBrown, Aug 08 2006
  

       If you would like to see how difficult this would be then go out and take your kids(or any kids) wagon. If you just hold onto the handle that is equivilent to backing a normal trailer.   

       Now tie the wagon handle to the back of another wagon. and see how well you do in backing it up. I suspect you will find that this menuver is VERY difficult as the intermediate "trailer" will not allow the trailer to continue to move until it jacknifes into the back of the car, at which point the trailer would begin to move in the desired direction.   

       Essentially the problem is that upon the start of backing menuver you turn to right, trailer turns to right. You straiten out and the trailer contiue to turn to the right until blocked by the vehicle.   

       I will attempt to draw a picture of what I am saying.   

       And [docbrown]contrary to what you might think, backing is not easy even for a pro, and I do not agree that adding an additional link will simplify the problem.
jhomrighaus, Aug 08 2006
  

       When pushing a trailer, there are two somewhat-conflicting goals: (1) aim the trailer in the desired direction, and (2) also have the vehicle aimed close to the desired direction. To accomplish #1, one must steer opposite the desired direction of travel. To accomplish #2, one must steer toward the desired direction of travel.   

       The problem with your proposal is that it's not only necessary to have the trailer and vehicle aimed in the proper direction, but it's also necessary to have the intermediate link aimed correctly as well. Instead of two conflicting goals, there are now three. Consider the task of trying to push a trailer straight north. All is going well except the tandem trailer starts drifting to the west.   

       If you were pushing a simple trailer, you would steer your vehicle westward to try to get behind where the trailer was supposed to be coming from. Your vehicle would then end up being aimed slightly westward as the trailer started being headed more nearly northward. You would need to steer your vehicle back to the north; if you time it right, the vehicle and trailer would head north simultaneously. The deviations in the vehicle steering would exceed any accidental deviations in the trailer path, but not outrageously so.   

       Now substitute a tandem trailer; the end trailer starts deviating westward. What do you do?   

       If you steer eastward, the middle trailer will deviate westward causing the end trailer to steer toward the proper line. But then what?   

       You need to have the middle trailer start heading away from its westward path, which means the vehicle has to steer west to get behind it. It has to do this with proper timing to ensure that the front trailer doesn't start going too far east. But you can't just end with the front two trailers heading north while the pushing vehicle is deviating westward. You have to get the pushing vehicle behind the middle section, and you have to do so with proper timing to ensure that it doesn't head too far east (and the timing must also be correct to get the front vehicle going straight).   

       Trying to push a tandem trailer without periodically pulling forward is extremely difficult even at "stop and think about it" speeds. The middle link may make one part of the procedure more "intuitive" but it totally messes up the rest.
supercat, Aug 08 2006
  

       Agreed [supercat]   

       You will almost NEVER see a Professional driver even think about trying to back a Tandem Rig. The only time they might consider is for a very short backup that is used to position the cab for a turn or something, even then they will avoid. Most will drop the Pup and park one trailer at a time, never 2.   

       See link that might help explain why this wont work. it requires twice as many manuvers to get to the same point and offers many more potential failure points.   

       Having trained several people on how to handle a trailer(not Tractor Trailer mind you just little trailers) I can tell you the easiest way to learn is to tell them to only look in thier mirrors, use the bottom of the wheel and then move thier hand in the direction the trailer has to go. 9 times out of 10 you should be able to back a trailer without breaking your grip on the wheel. The key is to go slow and move the wheel as little as possible.
jhomrighaus, Aug 08 2006
  

       I used to have an electric remote controlled car that I made a trailer for... It was next to impossible to back up, even with part-throttle and variable steering ratio capabilities. Just thought I'd add that in there...
Hunter79764, Aug 08 2006
  

       We once made a couple of trailers with super goosenecks. The ball was in the truck bed, and the arch of the trailer was so big that we could pivot the truck around and drive with the trailer in front. Backing the trailer was very easy that way. One of the fellows compared it to chasing chickens into a pen.   

       I now use the "chasing chickens" mindset even when backing a normal trailer. I just imagine that I'm scaring the trailer with the back of my car, and forget about rules for hands and turns.
baconbrain, Aug 16 2006
  

       Great idea - totally logical yet bound to end up a total disaster. More sillyness from the zen master.
wagster, Aug 16 2006
  

       looking in the mirrors helps a great deal when trying to reverse a big trailor as you can see it but i assume this "dolly" would be same width as the car and therefore pretty much invisable and therefore you could be perfectly hapy and smiling and thinking your doing a brill job at reversing when the dolly is jack-knifed and tearing your truck to bits! practise is the best way to be able to reverse! thanks Nick
randylandy666, Jul 27 2007
  
      
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