20 ft 15,000lb cap trailer

[Frank S]

Actually I built this trailer in 2002 shortly before I went to kuwait It was one of the first trailers I used Solidworks to assist in my design.
the frame is made of 4x6x3/8" angle with 3" junior I beam the tongue is 4x6x3/16" rect tubing the fenders and running boards are made of 2x4x1/8" tubing and 1/8" treadplate
The bed is 20ft by 6'6" overal width at the rear is 8ft 6 in tapering from the fenders to the front to 8 ft wide
from the rear to the hitch is 28ft overall
the axles are 7,500 lb cap each with electric brakes on both axles
I recently re floored the trailer with boards saw-milled from utility poles
This trailer has been pulled all over the country in the past several years just 2 years ago I pulled it from here to southern California then up to Seattle Washington and back with close to 17,000 lbs on it,My friend while I was in Kuwait has hauled everything from a case 580 backhoe to a couple of Mack trucks on it and even a 24 ft Winnebago on it from St.Louis to Houston.
We started the Title process before I left but in all that time until just last Friday it had never been registered So now for the first time in nearly 15 years and over 150,000 miles the trailer has tags on it that are not paper permits.




I made the tool boxes between the tires to carry straps and chains


Mounted in the tongue is the battery for the winch and the brake away safety
the hitch and tongue are designed for up to 6000 lbs of tongue load I could probably put 10,000 lbs load on it but the 2 5/16" hitch would be the weak spot
I normally use load equalizer bars on my receiver hitch


THe holes cur in the tubes are for weight reduction but mostly to add signature to the trailer

I made the equalizers 20 inches longer than stock to spread the axles this was to allow weight to be more evenly distributed on the trailer

the hole in the inner fenders are for placement of special hooks for chaining a load

note the rear rub rail and pockets for chaining and tail gate kit or to hook the ramps on
also all along the sides fo the trailer there are a series of paired holes 1 is a pocket for side biards the other is for passing the hook of a 4 inch strap through

[DIYer]

Thanks Frank S! We've added your High Capacity Trailer to our Trailers and Towing category,
as well as to your builder page: Frank S's Homemade Tools. Your receipt:

High Capacity Trailer by Frank S

tags: trailer, I-beam

[Grampa]

your concept for the double axle is excellent. I designed one similar many years ago for a company I worked for. We needed one that was easy to back up. from the configuration I would say this one is the same. it is clear you have some good understanding of the dynamics of a trailer. You will find that it is easy to handle and can balance it to provide a tongue weight so it can be towed by a small light weight truck. very good design. Keep up the good work and keep the designs coming......Grampa

[Frank S]

Grampa adding in the extra distance between the axles was primarily intended to allow a more even weight distribution for hauling large concentrated loads on the Interstate Highway system, behind a special built 1 ton conversion Chevy Suburban.
The normal distance on tandem axle trailers have a tendency to transmit a harmonic bounce to the coupling on many of the highways due to the way they are built this condition worsens during certain times of the year a condition in some states it is due to frost upheaval in other states it can be caused by extreme heat.
However stretching the center link spring equalizer posed a couple of issues you would not normally have with the standard length equalizers.# 1 being in order to maintain a reasonable amount of vertical tire movement the spring hangers had to be made taller instead of a normal 2 inches bolt center to frame height I made mine 4 inches with a 7 inch bolt center to frame for the center equalizer bolt instead of the 3 1/2 inches communally found for the type of springs I used. this gave me nearly 4 inches of axle travel over the regular 2 inches. This was needed since spread axle assemblies tend to be more susceptible to bottoming out on road way approach aprons from fueling centers as well as almost any driveway When the suspension system bottoms out on either axle that axle receives more of the load than the other.
Issue # 2 was with the spread system keeping the axles straight inline is more difficult I addressed this issue from what turns out to have been not the most efficient manor. I added guides inside of the extra long equalizers to limit their side to side movement. This works great for going straight down the road or even taking normal radius turns on the highway, but when making tighter turns there is a tendency to create extreme sidewall rollover and even some flexing in the axle itself. Since the trailer has over an estimated 150,000 miles on it if I ever start noticing wear in the system I will up grade by removing the guides and installing rubber or poly mounted bushings to the equalizers and torsion link bars to the axles. This will allow for more side movement in the tighter turns without the fear of breaking a spindle off, while maintaining axle alignment when traveling down the road.
One more issue is the body of the trailer really needs to be as level front to rear as possible to allow for maximum vertical travel of both axles since they are so far apart having the hitch too high or too low severely limits the travel of one or the other axle causing it to receive more load than the other. This is true for standard spaces axles as well but not nearly as critical especially on lighter duty trailers with Eye to eye link bar equipped equalizers where they might have several inches of movement.
Another thing about the design thought to this trailer was one day I might want to convert it to a goose-neck style.But instead of having a trailer with only a 20 ft bed I will build a drone the length of the tongue and mount the goose neck to that . Then I would simply pin it on over the tongue this would give me a 28 ft bed But that is just a long distance thought Since I actually built this trailer for a friend before going to Kuwait if I want a longer or more versatile trailer I will simply build another.