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Open Roads Forum  >  Fifth-Wheels

 > 40 ft. 5th Wheel Turning Radius?

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skylos

Columbus, OH

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Posted: 01/20/12 07:32am Link  |  Print  |  Notify Moderator

Math.

K = kingpin to rear axle
Y = kingpin to front axle
Z = truck front width

TRACK turning radius @ 90 articulation: (where the wheels rub the ground)

Trackradius = ((K+Z/2)^2 + Y^2)^0.5
TrackCurbToCurb = 2 * ((K+Z/2)^2 + Y^2)^0.5

J = rear axle to rear of trailer
I = width of trailer wheel track

Clearance required over curbs while making curb-to-curb tightest 90 degree maneuver:

ClearanceBeyondCurb90 = ((I/2)^2+(J-I/2)^2)^0.5

I IS possible to get the clearance EVEN TIGHTER if you can articulate some degree beyond 90 degrees, such that you rotate on the outside rear trailer tire for 90 degrees, then on the inside tire for 90 degrees which can be described by some calculations, but it involves yet another layer of abstraction calculating off the wheel at curb position rotations instead of the rear axle of the trailer rotating at its center, so I won't go into that... unless you ask me to. [emoticon]

I love trigonometry.

Hotel California

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Posted: 01/20/12 08:24am Link  |  Print  |  Notify Moderator

skylos wrote:

Math...I love trigonometry.


And now I remember why I didn't love math. Bottom line is: If the truck can make the turn, the fiver can make the turn. Except for the inside track of the fiver and obstructions. And exxcept for the outside rear edge of the fiver. Look at the back corner of many fivers on the road. Lots of dings and scrapes. Those folks were not good at math. I'm half good at making U-turns, half bad at making the same turns and half not good at fractions.


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ausie607

white lake

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Posted: 01/20/12 08:53am Link  |  Print  |  Notify Moderator

Francesca Knowles wrote:

As I understand it, turning radius is affected by both the length of the rig and the placement of its wheels.

I'm hoping somebody out there understands the math involved well enough to tell me how the formula would differ for a rig with the wheels (pivot points) situated differently than those on the rig in the picture.

When trip planning, the widths of ingress/egress roads and sharpness of campground curves is readily available...
It's be nice to be able to make a real determination of accessibility before deciding on destinations!


You are correct in saying that the turning radius is affected by the distance between the TV pivot point and the distance to the trailer wheels As the distance increases from the pivot point so does the turning radius.

Now to your second point, WT? are babling about. I have never in 40 years of camping seen an accurate scale map of a CG, nor have I ever seen any fools with formulas or calculators, standing in the CG roadway calculating the radius based on Pi laws. Once in Fl i did see an egret get run over, or was that an egress?[emoticon]

Francesca Knowles

Port Hadlock, Washington

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Posted: 01/20/12 11:33am Link  |  Print  |  Notify Moderator

skylos wrote:

Math.

K = kingpin to rear axle
Y = kingpin to front axle
Z = truck front width

TRACK turning radius @ 90 articulation: (where the wheels rub the ground)

Trackradius = ((K+Z/2)^2 + Y^2)^0.5
TrackCurbToCurb = 2 * ((K+Z/2)^2 + Y^2)^0.5

J = rear axle to rear of trailer
I = width of trailer wheel track

Clearance required over curbs while making curb-to-curb tightest 90 degree maneuver:

ClearanceBeyondCurb90 = ((I/2)^2+(J-I/2)^2)^0.5

I IS possible to get the clearance EVEN TIGHTER if you can articulate some degree beyond 90 degrees, such that you rotate on the outside rear trailer tire for 90 degrees, then on the inside tire for 90 degrees which can be described by some calculations, but it involves yet another layer of abstraction calculating off the wheel at curb position rotations instead of the rear axle of the trailer rotating at its center, so I won't go into that... unless you ask me to. [emoticon]

I love trigonometry.


[image]...um...

So THAT'S what those little ^^^^^^^'s above the 6 on my keyboard are for!

I love trigonometry too, and just as soon as my Tutor gets home from her 8th grade classes I'm going to sit down and try to learn some...[image]

Meanwhile, if you don't mind, a question:
Is that formula true for any/all lengths of "articulated" rigs- trailers as well as 5th wheels?

[image]

And thanks to everybody for all the info on how y'all make it work- please keep it coming!
It's all going into the "getting a grip on how it works " slot in my...database.


" Not every mind that wanders is lost. " With apologies to J.R.R. Tolkien

skylos

Columbus, OH

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Posted: 01/20/12 12:35pm Link  |  Print  |  Notify Moderator

Francesca Knowles wrote:


Meanwhile, if you don't mind, a question:
Is that formula true for any/all lengths of "articulated" rigs- trailers as well as 5th wheels?


No. hitches which cannot swing 90 degrees are limited to a different radius - there is a maximum articulation angle that they can reach. The equations are simplified by the case of the 90 degree articulation (right triangles), so its easier to present the results of the 90 degree articulation.

I would describe the more general case as...

The minimal turning circle more generally is thus, for all front wheel steered single articulated rigs:

The minimum turning circle is the circle which is tangential to the front wheel cut and perpendicular to the rear truck axle and passes through the point at the end of the rear trailer axle's outside end when the articulation between the truck and the trailer is maximized.

If you can't cut your wheel that hard (because the trailer is short) you'll have to do a multi-point turn to get your minimum turning circle for the trailer.

The equations to describe that circle could be written out, if desired.

[image]

Greentreena

British Columbia

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Posted: 01/20/12 12:52pm Link  |  Print  |  Notify Moderator

[image]


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2oldman

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Posted: 01/20/12 12:57pm Link  |  Print  |  Notify Moderator

I've seen that video. Clever, but I avoid 90° turns like the plague.

NC Hauler

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Posted: 01/20/12 02:16pm Link  |  Print  |  Notify Moderator

...As I stated earlier, and several have affirmed...no one is going to take a formula and "do the math" while/when towing....With practice, you'll learn how your 5er tracks...and again, one of your best "tools" is your mirrors, learn to use them and a spotter, (my wife[emoticon]), has come in handy more than several times...(walkie-talkies have been handy also with the spotter)...

"practice makes perfect"...


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Greentreena

British Columbia

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Posted: 01/20/12 04:14pm Link  |  Print  |  Notify Moderator

2oldman wrote:

I've seen that video. Clever, but I avoid 90° turns like the plague.


I keep that move in my back pocket in case I find myself in a pile of trouble. I'm sure its hard on the tires and axles. I've never tried it yet.

NC Hauler

Pence Springs WV

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Posted: 01/20/12 06:11pm Link  |  Print  |  Notify Moderator

...These 5er's and TT's that we own are designed, to some extent to take the "skewing" of the tires when making a very sharp curve....Manufacturers understand that this could happen more often than not.....I would think if it were "all that bad" to do, there would be a disclaimer of sorts or a WARNING in ones PDI, Sales Pitch, in the Instructions that come with ones unit, or at the very least, a WARNING LABEL located somewhere on the unit telling one to refrain from making sharp curves, (ie, U-turns, etc).....

I've never seen that warning in any literature that I had with a TT or 5er. Again, these units, have HAD to have been designed to some extent to take U-Turns...maybe not with alarming frequency, but again, IF it were REALLY bad to do it, I would think we would read more about it as a warning somewhere....Axles, wheels and tires are made to take a sharp curve to some extent and maybe more often than some would think on these forums...It's part of owning one of these....

EVERYTIME I take my 5er out and bring it back; to back it into my driveway, I have to make a U-Turn in the cul-de-sac I live in....Don't know how many times over the almost 6 years I've owned it that I've done this, but I keep an eye on wheels, tires, axles , shocks, spring packs, brackets and welds and I've yet to see any damage from this maneuver...I don't go out of my way to do this, but it's something I've never been concerned about doing. Again, I'm pretty sure the design engineers had to take this maneuver into consideration when they designed the 5er....if not.....where's all the warnings NOT to do this maneuver with one's 5th wheel??

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