Trailer Length and tracking

Chorky

Observer
So from all the research I have done, I generally understand the following to be correct:
IF the trailer axle width matches your tow vehicle, and the trailer center axle to hitch length matches the tow vehicle wheelbase, THEN in theory the trailer will follow in the tracks of the tow vehicle exactly.

There are plenty of sites and documents to support this theory. Now naturally it can get into more advanced discussions with the amount of overhang a truck has behind its axle (as in a stinger - logging truck style), and such, but I think those numbers to have minimal effect as in my case I believe the rear overhang would offset itself and am not using a hitch extension as some with campers use.

Based on this, I would understand that the theory would mean that a F350 with a wheelbase of 168" (14'), would optimally want a trailer with said axle-hitch length. In my case, a 21' springdale with a 15' center axle to hitch length.

So, based on this, does anyone happen to know any actual calculations, to say, figure out how much corner cutting would occur if a trailer, say, had a 18' length from center axle to hitch? So being 4' longer? I'm sure the math is out there somewhere, and probably could figure curvature out myself given enough time, but just curious if theres a calculator someone knows of. I know my trailer, being a foot longer and a 8' wide wheelbase as opposed to the 81" of the truck there is a 6-12" cut of corners. But would like to see the math/engineering behind this.


Basically, trying to figure out how much cutting a trailer of X length would have as opposed to my current trailer - as that may have an effect on future purchases seeing as how some roads really can get tight.
 

takesiteasy

Adventurer
So from all the research I have done, I generally understand the following to be correct:
IF the trailer axle width matches your tow vehicle, and the trailer center axle to hitch length matches the tow vehicle wheelbase, THEN in theory the trailer will follow in the tracks of the tow vehicle exactly.
....

Here's a link to an offtrack calculator: http://toxiccelery.co.uk/Offtrack/Offtrack.html

If you read it closely, you will see that your theory is not quite correct.
 

mobydick 11

Active member
In the real world ,the shorter the trailer or closer the axle to the ball . will be the closer it follows the track of the back axle of the towing vehicle. If you want a trailer to track exactly to the back axle of your truck. My non scientific view would be . Match the exact distance from the center line of the truck axle to the ball ,as the ball to the trailer axle . This would be like a front end loader . If the pivot point is centered between the axles then it tracts true . This trailer would be terrible to back up though . Your theory will probably make for a very nice towing and backing trailer .
 

mobydick 11

Active member
Yes I agree this is not a good formula to build a functional trailer . all we can do is buy or build the shortest trailer that can carry your gear ,and learn to live with it. But I guess I am not answering the question,sorry .
 

gatorgrizz27

Well-known member
I can’t give you exact numbers, but I can tell you that’s not a rig I’d want to drive anywhere that’s considered “tight”, it will track inside the truck’s path a lot, and I pull trailers almost daily.

I’d start by drawing a circle the diameter of the turning radius of the vehicle. Then figure out where the ball will sit, based on vehicle wheelbase intersecting the circle. From there, draw a straight line the length of the trailer centerline from hitch to axle. What I’m not sure of is how you determine the angle of that line. Adding half the width of the trailer track perpendicular to the back of that line should show you the trailer turning circle.

One other thing to keep in mind is having a longer tongue or hitch to trailer axle length allows you to “catch up” to the trailer and maneuver it with less space. If your trailer is too short, once it starts turning tighter than you want it to, there is no way to correct it other than stopping and pulling forward.

On a small Jeep/military type trailer, I think the ideal thing is to build the tongue as short as possible so it follows well on trails, using a 2” receiver with the tongue slid in a ways, so it can be extended for easier backing and carrying kayaks, etc when trail work isn’t needed.

I’ve found a 130” wheelbase with a standard pickup truck rear overhang, and a trailer that is 16’ overall and roughly 12’ from hitch to axle is about as long as I like to deal with.

I did tow a ~30’ gooseneck with a CCLB F-250 for awhile, it takes a lot of maneuvering.
 
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Chorky

Observer
I can’t give you exact numbers, but I can tell you that’s not a rig I’d want to drive anywhere that’s considered “tight”, it will track inside the truck’s path a lot, and I pull trailers almost daily.

I’d start by drawing a circle the diameter of the turning radius of the vehicle. Then figure out where the ball will sit, based on vehicle wheelbase intersecting the circle. From there, draw a straight line the length of the trailer centerline from hitch to axle. What I’m not sure of is how you determine the angle of that line. Adding half the width of the trailer track perpendicular to the back of that line should show you the trailer turning circle.

One other thing to keep in mind is having a longer tongue or hitch to trailer axle length allows you to “catch up” to the trailer and maneuver it with less space. If your trailer is too short, once it starts turning tighter than you want it to, there is no way to correct it other than stopping and pulling forward.

On a small Jeep/military type trailer, I think the ideal thing is to build the tongue as short as possible so it follows well on trails, using a 2” receiver with the tongue slid in a ways, so it can be extended for easier backing and carrying kayaks, etc when trail work isn’t needed.

I’ve found a 130” wheelbase with a standard pickup truck rear overhang, and a trailer that is 16’ overall and roughly 12’ from hitch to axle is about as long as I like to deal with.

I did tow a ~30’ gooseneck with a CCLB F-250 for awhile, it takes a lot of maneuvering.

Well, I can say I've had that combo in some pretty darn tight spots already. Places most wouldnt' want to go with just a normal truck... So, that doesn't really scare me much, just gotta be cautious and slow. But, as you said for comfort sake and manuvering, I think that if one were to build a trailer that, by geometry, would in fact track nearly perfect behind the rear truck axle, it woudl reduce much stress about cutting corners on a full bench road. So I would like to calculate, for example, (at least in theory) if you had a trailer of X length (axle to ball), with a given X overhang of my truck, and X wheelbase, what the actual cutting would be. I'm pretty sure that the angle of the line as you mention would be determined by some geometric calculation of the turning radius of the truck, the steer angle of the wheels, the wheelbase, and the rear overhang of the ball behind the center of the rear axle. And further some calculation to add a trailer of X width and X length from ball to trailer axle centerline. I could figure it out longhand, but would rather find a calculator - i know they exist. finding a simple one seems difficult.


Here's a link to an offtrack calculator: http://toxiccelery.co.uk/Offtrack/Offtrack.html

If you read it closely, you will see that your theory is not quite correct.
Sweet thank you. I'll check this out this weekend. I did find other databases that are used by european engineers to ensure that a new truck/trailer combo will sufficiently track and navigate tight neighborhood streets, but it was a very intense program and more than what I'm looking for. This seems to be much more simple.
 

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