Building An Offroad Trailer From Non-Offroad Plans

A good question from some of our customers:  “I want to build an offroad trailer, but I can’t seem to find the right trailer plans to build it.  Is it better to buy the 4 x 6.5 – 2500# – Off-Road Trailer Plans, then enlarge it, or to buy one of the other trailers and  beef it up?“

That is a good question, and I have answered similar questions briefly for customers a number of times.  That probably means even more people are thinking about it, so, let’s dive in an give a full answer.

The most common versions of the question involve the trailer sizes of  5′ x 8′ -and- 5′ x 10′.  We will use the 5′ x 10′ as our example in this article, yet the answer is very similar for a 5′ x 8′ -or- 6′ x 8′ -or- 6′ x 10′ trailer size.

Disclaimer:  I speak only for the Mechanical Elements trailer plans.  I know these plans because I designed them, and I know what they are capable of.  Extrapolating the information below to plans from other sources may or may not be a good idea.  Many other designs are comparatively weak, so I will leave the choices, and judgement, to you.

What Is Offroad?

This term, “Offroad”, has different meanings to different people.  So, when you think of “Offroad”, what do you mean?

Do you think about offroad as dirt roads, fire roads, and occasionally an excursion off the path?  Or do you mean serious off roading like 4×4 trails, rock crawling, and deep river crossings?

For the sake of this article, we will consider 3 places people drive.

1. Roads.  – Any place a normal production vehicle is intended to drive.  Paved roads, dirt roads, dirt driveways, etc..  (This is not a function of temporary conditions like weather (snow and ice), etc..  Think normal.
2. 4×4 capable.  – Any place a normal production 4-wheel drive vehicle can go.  A little steeper, a little more ground clearance, and other typical conditions.  Off the “road”, maybe fire roads, the remote campsites, etc..

   

3. Places that require vehicle modifications.  – Raised for added ground clearance.  Bigger than stock tires.  Lockers, etc..  See the next photo below.

Now don’t get crazy with the exceptions.  Sure, there are plenty of variations where one production vehicle will struggle, and another will not.  There are also crazy folks that take nearly stock 4x4s where they probably should not.  We can use these 3 categories as a general perspective as we consider the build for an offroad trailer.

Ground Clearance For An Offroad Trailer

Ground clearance is one of the main factors in where a trailer can safely go.  It is not just the clearance, but also where the clearance is.  There is clearance under the axle which is one important place.  Yet, arguably the more significant clearance for an offroad trailer is approach and departure angles.  This is one of the reasons that Jeep trailers for rock crawling are often so short.

With respect to our trailers, we normally consider the road categories 1 and 2 pretty generic.  All our trailers can do Road condition 1 – with the possible exception of ground clearance for offroad.  The related approach and departure angles can create trouble in some situations.

Ground clearance is the limiting factor for some of our trailers for road condition 2.  While the frames are strong enough, the clearance might not allow it.  (Ground clearance is less by choosing a drop axle with many of our trailer plans.  It is desirable in some situations, but not in others.)  That is important if you build an offroad trailer.

Getting into the areas of offroad conditions 3, takes a little more work.  This is why our 4′ x 6.5′ – 2500# – Off-Road Trailer Plans are in the “Specialty” list, rather than utility.  It is not that the frame is so tough, because all our trailers have tough frames.  It is more because of the accommodations for ground clearance and the resulting approach and departure angle improvements.  The photo above shows the value of a short trailer in serious offroad conditions.

Load Range

For ground conditions 3, most of the time we are talking about something pretty light.  A lot of people want to take a mini camper into the hills with them, or a small trailer for gear.  For our purposes, we will focus here on something in the range of 2000 lbs or 2500 lbs.

We can extrapolate that a little higher pretty easily, but we will keep this discussion to a single axle.  (Articulating a tandem axle for rock crawling is quite a trick, so we will leave that out for now.  (Read the article about axles with no suspension for a bit on that.)

If you want a trailer for conditions 2 above, the below modifications will work.  Please note that the longer the trailer is, the less of the technical crawling stuff you will be able to do.

If you are looking for conditions 3 above, better stick to a short, light trailer – or really focus on the skid plates.

Concepts To Build An Offroad Trailer

Our experience shows a few things of big importance to build an offroad trailer.  All of these interrelate.  In this instance, we are using the assumptions noted above for a desired 2000 lbs capacity, 5 x 10 trailer:

1. 1. Tires:

      The biggest gains for offroad (to improve both ground clearance and handling bumps) are with tires.  Large tires, with low-ish inflation pressure can help a lot.  We suggest truck tires for an offroad trailer build, and while there is some argument, read this for more tires info.

      To use the bigger tires, we also recommend a stronger axle.  Get one rated for more than you need so it has extra spindle strength, larger hubs, and bigger bearings to handle the big tires and the rough roads.

      

      Side note:  If wheels and tires match for both trailer and tow vehicle, it gives many possibilities to conquer issues.  The spares work for both.  It is more expensive, for sure, but worth it if you’re going extreme.

   2. Torsion Axles:

      To get more ground clearance, use torsion axles with a start angle down.  They go down to 45 degrees.  You will lose some compliance with a large down angle, but that is OK, because you will gain compliance with the larger, underinflated tires.  The angle down gives more ground clearance under the axle.  (If the plans you purchase do not have a torsion axle, get the torsion axle conversion plans also.)

      
      For even more clearance, add material between the torsion axle mounts and the trailer frame.  This does not change ground clearance for the axle beam, but it can definitely improve approach and departure angles.  Basically, more ground clearance for the front and back of the trailer.  It is like adding a lift kit to your vehicle because it raises the trailer frame.  With the angle down, plus some lift, the trailer will have more ground clearance than the tow vehicle.

      A really nice thing about the Dexter Torflex axles (and other brands) is you can order them in various capacities.  At the factory during axle construction, they put in a little more or less of the rubber cord to meet your desired capacity.  It is a cool system and it really helps in a situation like when you build an offroad trailer.

      So, if the trailer is 2000 lbs, upsize the axle from a Dexter Torflex 9 to the Torflex 10, and order it with a load capacity of 2500 lbs.  We want a little extra capacity for offroad conditions.  We also want the larger spindles, bigger bearings, and larger hubs of the Torflex 10 axle.  This, combined with larger lower pressure tires will give both the strength and the soft ride we want for offroad.

   3. Tire Pressure:

      For tires, large diameter is your friend offroad.  It helps roll over things better.  However, most larger tires have more capacity than you need, so we use lower air pressure.  Don’t go crazy with low pressure, you do not need it for traction like with the drive vehicle, you only need a little tire compliance.

      For example, if the tire has 2094 lbs capacity (load range 106), but you need 1250 lbs (half of the 2500 lb axle).  We take the normal pressure for the tire, for example 40 psi, (not the max pressure), divide that by the tire capacity (2094) and multiply by actual capacity (1250).  This example comes out at 24 psi.  That will keep the tire on the rim, while it softens some of the bumps.

      In reality, tire pressures are not mathematically linear like this example implies, but because of sidewall stiffness in the ranges we are talking about here, it works well enough.  You can experiment with lower pressures, but be careful.

   4. Lift Spacers:

      To get the most for ground clearance, we can also lift it.  This is just like lifting a car, but less sophisticated.  As above, it does not change ground clearance for the axle beam, but it will increase approach and departure angles.

      

      In our plans we specify a “Torsion Axle Mounting Bar” which welds to the frame as the place to bolt the axle.  When you build the offroad trailer, we can add ground clearance with a spacer between the frame beam and the “Axle Mounting Bar”.

      The hiccups with lifting like this are three.  1)  The deck height also raises, so getting into your trailer becomes more difficult.  2)  A higher Center of Gravity decreases the trailer tip angle.  A narrow tall trailer will not do 4-wheeling so well.  3)  Any instability will get worse as the Center of Gravity becomes higher, so pay close attention when loading the trailer.  Proper tongue weight, axle position, heavy things at the bottom, etc..

   5. Skid Plates (and other Protections)

      Handling the scrapes is a big deal.  We talk about approach and departure angles, and that is important for offroad.  Make sure you protect your trailer – front, back and center – from serious scrapes.  More important for longer trailers, and more important for the more challenging terrain.

      We will put a specific highlight on the hitch.  This coupling area is often abused – because it is often the low point.  See the discussion about adjustable hitch geometry.  Even if you do not use an adjustable hitch, take note of the concepts, and apply them also to other things, like the jack, battery box, tongue tubes, etc. as low points that can scrape.

      We recommend adding smooth places to scrape, with rounded edges so the trailer does not catch an edge and bend or break something.  The back bumper and the front corners, for instance.  These should have accommodations to allow them to slide easily over a rock if it catches one.  Any other place of particular importance.  Of course, we temper this to the need for the driving in the conditions you expect.

   6. Finally, the Hitch

      This is an often neglected part.  Whatever the size of your trailer, and no matter what type of hitch you want, we recommend going one size heavier.  Put a Class III hitch on your Class II size trailer.  Take a similar step up for other trailers.  In offroad conditions, the hitch takes abuse, so beef it up.  It is a cheap upgrade.

   Modifying Trailer Plans

   Now to the original question.  “Is it better to buy the “4′ x 6.5′ – 2500# – Off-Road Trailer Plans” and enlarge it, or buy plans for another and beef it up?”

   We do not recommend expanding a trailer as much as required if you start with the 4′ x 6.5′.  Read here for what is OK.  It is much better (and safer) to start with trailer plans for something too big and reduce a little.  So, since we want a 5′ x 10′, we can start with that, then build an offroad trailer.

   The 5′ x 10′ – 2000# – Lightweight Camper Chassis is for a camper chassis.  If that is what you are building, at 2000 lbs or less, then that is the right place to start.  Lift it a little, upsize the axle with large tires, and it will work great.  This can be a great build for an offroad camper trailer, like a teardrop or square drop.

   If you want something a little more robust, use the 5′ x 10′ – 3500# utility trailer as your base.  It is a little heavier frame, but it will certainly take the offroad duties nicely.  Downgrade axle capacity  to the load you need to carry (for a softer ride), and that trailer serve well.  If you want the full 3500 lbs capacity, upgrade the axle to a Torflex 11.  Have the axle made for 4200 lbs capacity.  Yes, it is a little more stout, but the added benefit of yet larger spindles and bearings is worth it when you build an offroad trailer.

   The same is true for our 6 x 8 -and- 6 x 10 trailers.

   Build It Well

   Both the design and the build are keys to success.  We take care of the chassis design, but the build of an offroad trailer also includes the design of the upper portions.  Whether that be the cargo holding, or the camper body, both design and execution are important.  To that end, the article about where you put weight in your trailer is good information.  Design it to be stable, not just the chassis, but the whole trailer.

   Our slogan – Build it well, and it will serve you a lifetime.  That is also true when you build an offroad trailer.  Don’t go cheap on the parts, build in a few extra gussets, and take care to build it well.

   OK, we have a lot of good info here, so hopefully that gets you going.  We wish you the best of luck in your project.