Trailers – How to Design & Build

Guilherme Campos

2 Sep, 2023 11:33 PM

This is at least the second or third major version of this book and hopefully the final version. After 14 years of writing, rearranging, drawing and calculating we have found that it will take three volumes to present this material. The first volume has six chapters which include most of the things people think about when they think about building a trailer. The 2nd and 3rd volumes cover calculations and other technical aspects which are also very much a part of building a trailer and often don’t get included in the process. Frame strengths and towability are covered in Volumes 2 and 3. If you actually do intend to design and build your own trailer, reading and understanding all three volumes will help you understand many of the basics necessary to start and work through your project. The information in this series applies primarily to trailers under 7500-lbs gross capacity. Some may be applicable for larger trailers but an expert should be consulted.

1. Step 1: Trailers – How to Design & Build

   

   
   

   NOTES

   This is at least the second or third major version of this book and hopefully the final version. After 14 years of writing, rearranging, drawing and calculating we have found that it will take three volumes to present this material. The first volume has six chapters which include most of the things people think about when they think about building a trailer. The 2nd and 3rd volumes cover calculations and other technical aspects which are also very much a part of building a trailer and often don’t get included in the process. Frame strengths and towability are covered in Volumes 2 and 3. If you actually do intend to design and build your own trailer, reading and understanding all three volumes will help you understand many of the basics necessary to start and work through your project. The information in this series applies primarily to trailers under 7500-lbs gross capacity. Some may be applicable for larger trailers but an expert should be consulted.

   Volume 1 has been divided into six chapters. Chapter 1 and 2 are introductory. Chapters 3, 4 and 5 cover components. Chapter 6 discusses the actual building and assembly, cutting, layout, welding and painting. Major suppliers are listed in the Appendix. If you have no place else to start searching, this is a good beginning. Other beginning ideas can include recreation areas where people use trailers. Find one you like and use it as a starting point. Use the cautions in these books to evaluate and improve upon that existing design. Do be cautious because some trailers aren’t what they seem, as we discuss here.

   This book is a record of my experience building trailers and is in no way “the Gospel.” There are certainly other ways of doing it which are just as effective. The advantage of a book is that you have the choice of using the information or not. The disadvantage is that you often have no one to check the manner in which you choose to use the information. As a result it is difficult for us to take any responsibility for what you can create or what you do create. Remember this as you read or use the information contained here. Make sure it makes sense to you and to your situation. If you have any questions about it, be sure to consult with someone who has the necessary knowledge to help you.

   ACKNOWLEDGMENTS

   As with any book, it takes more than the author to complete it. And with a technical book of this nature, this step is especially important. In the beginning, Rich McCormack of Newport Press helped with the concept and initial formatting. Overall editing and finding of those infamous little errors was done by two trusted friends—Wendy Jo Block, a journalism expert and R. E. Williams, a technical expert in the field of engineering.

   Typing the first draft of the manuscript (and a few thereafter) was the tedious doing of Delores McTaggart with an old fashioned typewriter. Finally in 1987 drafts were transferred to the Macintosh computer. From there, the book began to take its present shape. Debbie West and Paulette Kelly tirelessly revised draft after draft on their own computers as the book was transformed into its present configuration. And now thousands of hours later with numerous corrections, additions and changes behind us we have a 100 page book which has grown to two volumes of almost 200 pages each.

   Although the majority of drawings in this volume were done from my own knowledge, data for some was gathered from other sources. Especially helpful were the people at Kruse Feed & Supply in South El Monte, California who assisted me with weighing of alfalfa bales when I showed up with a scale. Comments on Chapter 3 were solicited from my friends at Century Wheel & Rim Richard Starks, Gene DiSano and Jerry Milsap. The ade calculations in this same chapter were checked by Ken Foster, a structural engineer and Merle Bolden, a trailer engineer with Century. Wheels and tires for photographs were provided by Al Featherstone at Industrial Tire Company. And Dan Guinn of D & G Welding in Littlerock, California provided his plasma cutter and heliarc welder for photos used in Chapter 6.

   And I certainly must thank all the torsion axle manufacturers for their assistance in providing information to make a thorough discussion of torsion axles possible. Norm Reynolds of Torax wrote a 5 page detailed letter about the benefits of torsion axles in general and more specifically the benefits of steel torsion axles. Don Boerger and Vic Rosengarten at Henschen were also extremely helpful in providing useful test data and general technical information in this area. Conversations with Vince Scott of UCF and Mike Platz of AL-KO rounded out the subject of torsion axles. Mike Platz also looked up and sent me a large amount of data and literature on mechanical brakes commonly used in Europe.

   Ron Haase at Dutton Lainson provided accurate information on bearing protectors and an engineering drawing, included as an inset in one of the Figures in Chapter 3. John Bechtold of Unique Functional Products also took the time to discuss the benefits of bearing protectors and send photos and drawings.

   Tom Kneiss of Hammerblow Corporation referred me to a distributor, AgServ West where John McKeon, Jr packaged and sent several heavy duty trailer jacks for the photographs in Chapter 5. Thom Perry and Julie Dunham from SuperwinchTM sent a chart describing methods of calculating winch strengths for use in Chapter 5. Charles Perry followed with an additional detailed letter providing information which has been added to this newer version.

   Photography in general was largely my doing with many photos taken from files of vacations across the Southwest. Most product pictures were chosen from the IRD library of photos, which were also taken by the author. Some product photos were provided by Hammerblow, Unique Functional Products and Dutton Lainson. The Mubea ironworker photo shown in Chapter 6 was the courtesy of Steve Cashion of Meyer Sheet Metal Machinery in Los Angeles. As you can see it takes effort from many people to compile the information necessary to write a complete book. We must all be extremely grateful to these people (and I sure hope I haven’t missed any), because they helped to fill in areas of the book that were weak or non existent. Luckily, my 18 year tour of duty in the trailer manufacturing business was instrumental in providing the foundation .

   SAFETY FIRST, LAST & ALWAYS!

   This book has been written to improve your safety and the safety of trailers in general—not decrease it. We believe that increased knowledge is a prime key to your building of a successful trailer. Bear in mind though that all the knowledge needed is NOT included here. There are so many aspects to a project like this, we can’t possibly cover them all. This book contains few outright recommendations and is merely a list of specifications for items used to build a trailer. How you combine these parts and pieces is beyond our knowledge and control. Any trailer designs you concoct must be carefully considered and done with the entire system including the tow vehicle as part of your thinking. Due to these facts and the immense number of variables, what you create is your own responsibility.

   Remember, changes to improve the trailer’s towability may decrease the tow vehicle’s performance or put extra strain on the trailer’s structure. TRAILERS – How to Buy & Evaluate discusses some of these aspects. Volume 2 and 3 look more closely at concepts and describe calculations one might want to perform to gain insight into these areas while designing a trailer. Any newly built trailer should be checked out and road tested slowly and carefully, preferably in some remote unoccupied area, such as an empty parking lot or test track designed for such maneuvers. An extra wide EMPTY boulevard as one might find at 6am Sunday morning may be more accessible. Freeways, city boulevards and winding mountain roads are least desirable and not recommended. As you venture forth, listen and watch for sounds and sights of trouble. Be sensitive to the movements of the trailer and don’t risk anything. Remember that instability can be initiated by downhill grades, wind gusts or passing trucks (to name a few) and caution is the watchword here. Speeds must increase slowly, and any hints of instability heeded and checked immediately and thoroughly. Please don’t just keep driving in hopes it will just disappear. An inherently unstable trailer may not show its colors until it’s too late. If available, the use of test equipment can improve your perceptions and knowledge.

   Because your ability, along with the resulting combinations, modifications, materials and methods used are beyond our control, naturally we cannot assume any responsibility as to the results obtainable. Bear in mind that building a trailer for use on public roads is serious business, as are any vehicle modifications you may attempt. And while few laws exist as restrictions to your design choices, common sense and an accurate assessment of your abilities is imperative to assure your safety.

2. Step 2: Developing a Desing Trailers

   

   Designing and building your very own trailer can be fun and very rewarding. To embark on such a project, work through the myriad and numerous questions that inevitably occur and end up with something that will haul whatever bounty you have is worth more than just a pat on the back. But beware … this project is fraught with pitfalls and actually carries the potential for creating a lethal weapon. Yes, if your home-built trailer is constructed poorly, it and your tow-car could be so unstable at certain speeds as to become a life threatening risk—one you cannot control. The information in this book and its Volume 3 will provide many of the keys to avoid such a disaster. TRAILERS – How to Buy & Evaluate also contains a simplified summary in the event Volume 3 is not yet available.

   Yes, trailers can be built and hooked to a tow vehicle that are a delight to tow. These trailers don’t just fall together by accident. They are tediously and carefully planned using the principles of structures, dynamics and basic engineering laws. In addition, components are selected to be appropriate and optimum for the job.

   Don’t underestimate the size of this task … or the impending responsibility of building something that will not risk your own life or the lives of others. Don’t assume your Motor Vehicle or Police Department will check out your trailer for design, towability and safety. They are not engineers. They are there to enforce the laws, not provide you with design expertise. All you can count on your Motor Vehicle Department to do is verify that what you’ve built is indeed a trailer—not an auto or a truck or a bus—and assign a serial number to it. They also will check for lights and their correct placement, as well as add a serial number to your frame. After you have studied this book and understand its contents, you will know so much more about constructing a trailer that you may well be able to tell them how to build one. However, I don’t suggest you do that.

   This book is a record of my experience. It has information in it which can possibly be of help to you. It can guide you through the inevitable challenges and be an excellent reference book, there to answer questions when needed. Designing something can be a lot of fun, especially if you have the energy, enthusiasm and focused will-power to carry through the construction and end up with something useful, something you understand stem to stern because you’ve taken the effort to study the physical laws that affect its performance.

   
   

3. Step 3: Steps to Organization & Success

   

   
   

   
   

   The first step in any project is to PLAN with a capital P-L-A-N! This may seem boring and unnecessary, especially when you can just walk to your shop or garage and start welding something together. Welding it together first and planning as you go locks you into something you may find later isn’t appropriate. Use a piece of paper to start your building … and we’ll show you how easy it is to correct your mistakes before they’re cast in concrete … or steel, as the case may be. If you want to make a change just get out your eraser … or a clean sheet of paper. By the way, spouses tend to like the economies of this method, too.

   As you draw, you will find groups of questions popping up that need to be worked through before you can finish drawing something. The correct design approach involves a whole series of “oh no, not again”… and “what do I do now?” This confusion can be terribly unsettling. But the success of the final product depends on your perseverance in thinking these things through. It may appear to be a lot more effort than the actual building. But that is only because there are so many questions brain-work and maybe foot-work to answer. If you follow a standardized procedure in answering your questions you can check off the steps as you go and it will seem a lot easier. Let’s look at these steps in detail so you know what to expect and have a pattern to follow.

   The process for designing a trailer is the same as for designing anything else. It involves a step by step sequence which leads to an end product. Each step can be rather involved and take a lot of time. But please don’t despair. Properly attended to, each step will lead to the next and may answer questions you’ll have further downstream. Before you know it everything will fall together and you’ll be at your last step. The steps to guide you to success are as follows:

   
   

   
   

   1. State the problem (basic requirements for the trailer);
   2. Lay out the basic product using only general, basic dimensions;
   3. Investigate thoroughly the options available;
   4. Calculate material sizes and overall configuration;
   5. Select materials using calculated answers as a guide;
   6. Decide on final dimensions to be used;
   7. Investigate & select all components;
   8. Determine relative positions of all parts and pieces;
   9. Lay out the final design using chosen parts and pieces;
   10. Transfer all info to the final layout.

   These steps are not necessarily done in this order, although it is the order in which you will first encounter the steps. New information obtained in any one step may modify a decision you have already made and cause you to rework a previous step. This checking, changing and rework gives you the ultimate design. It is important to let this process occur; don’t allow yourself to become impatient or say “I’ve already done this.” Do it again and again until it is as perfect as you can get it.

   It’s all done on paper with a pencil, a few straight edges, triangles and lots of erasers. Some of these useful tools are pictured in Figure 1.1. These are the same ones you may have used in high school drafting class. Hauling out that old high school equipment will bring back some memories along with a raft of useful tools. And for us frugal folks using what we have can be a financial boon.

   Tools in the form of tables, equations and methods are also necessary. Volume 2 discusses this aspect of design. Used in conjunction with your drafting tools, they give you what it takes to put a trailer design together. All it costs is time – no investment in metal before you’re ready. A few chapters into this book, the whole process will be more familiar and comfortable and the steps will fall into place.

   Setting goals is another useful tool for moving your project forward. Although your overall goal is to build the trailer, setting your first goal at some intermediate point will minimize discouragement. In fact, if the overall goal to build a trailer is your focus, the importance of a drawing can be easily underestimated—sometimes enough to cause you to completely ignore it. After the drawing is done, though, your next goal can be to specout all the required materials; next to buy the materials … and so forth.

   Doing it step by step in this manner is much more approachable than looking to the overall completion of a hand-built trailer.

   As you read through this series of books, Volume 1, 2 and 3, many of the complex technical terms you need to understand the trailer, the tow-car and the combination vehicle (trailer and tow-car together) are defined and explained. Use the steps to simplify your project, to give you a guide-line and help you make decisions before you cut metal. The steps will help you in building any project. As you read through this and the next few chapters, continually refer back to the original outline to keep you on track.

4. Step 4: STEP 1. State the Problem … or Define the Project

   

   The problem statement is very important. It gives the basis from which to launch your whole project and defines the performance requirements for the finished project. Engineers often refer to this step as completing “half the battle”. Once a problem, or project, can be defined, it can be clarified and worked through. A trailer that dangles as an idea in your imagination can never be manifested into something useful.

   So how do we turn our “ideas” into a problem statement? Start by putting your thoughts on paper-whatever those thoughts are. This doesn’t mean talking about them with all your buddies—that can waste precious energy. It means getting out a pad of paper and starting to write. If you enjoy the pad, paper and pencil you’re using you’ll be able to sit in one place long enough to really think things out. Having the correct drawing or writing tools will turn those “ideas” into something real on paper. Writing things down provides a starting point for organization. Some thoughts you might include regarding your trailer are:

   
   

   1. Cargo dimensions & weight;
   2. Tow vehicle size & specifications, horsepower, wheelbase, rear overhang;
   3. A list of places you might take your trailer;
   4. The miles you intend to tow your trailer;
   5. A list of tasks your trailer may be called upon to perform;
   6. Some sketches of what you think might work;
   7. The storage space available for your trailer.

   
   

   From these … and a few more facts, you can put together what is called “A Problem Statement” which in reality is a definition of your project. The word “problem” is used because it’s what we used in school and it tends to put you in the right frame of mind to analyze all aspects and options. This problem statement might include the trailer’s primary use, its auxiliary use and whether it is to be light weight to save gas or extra heavy duty to withstand abuse. Below is an example statement.

   
   

   Sample Problem — Hauling boxes

   
   

   1. Primary use – hauling boxes filled with books
   2. Cargo weight: 24 boxes @ 60-lbs each = 1440-Ibs.
   3. Cargo dimensions: each box is 12″x 17″x 36″ high
   4. Distance travelled: 30 miles x 2 trips per week = 60 miles/week = 6240 miles/year.
   5. Trailer doesn’t need a cover in sunny weather but provisions for a canvas cover would be nice.
   6. Trailer cannot weigh more than 550 pounds since the tow vehicle specifications recommend a maximum trailer weight of 2000 pounds.
   7. Want to be able to use the trailer on week-ends for recreation—this will increase the mileage by about 5000 miles/year.

   
   

   
   

5. Step 5: STEP 2. Lay Out the Basics

   

   
   

   A picture is worth a 1000 words. And getting your trailer from your imagination onto a piece of paper can quickly tell you whether you are envisioning something workable. Although this step calls for only a “rough” sketch, it may not seem so rough if you are unaccustomed to “sketching” things to scale. And yes, it should be done on grided paper to some small scale so that it will fit on an 8-1/2-in x 11-in sheet of paper. This size makes it easier to file the drawing and slip it under the spring of a clip board. Using a clipboard has an ulterior motive because it means you can take it with you to relax in a big soft chair. In this way getting the drawing onto paper becomes relatively painless. Of course, if you’re a diehard for straight back chairs and rigidity inspires you, use a desk and a nice large sheet of paper.

   If the trailer is really big, though, two letter size sheets could also be used to produce a drawing 11-in x 17-in. À more detailed description of your options in the realm of scales is shown in Figures 1.3 and 1.4 on the next two pages. Following that, on pages 10 and 11, is a background grid, reproduced as Figure 1.5 of this book. Use this if other sources seem to leave you empty handed. Copy this grid onto an 8-1/2 x 11 sheet of paper, it will give you something to start with. Next select an appropriate scale from Figures 1.3 and 1.4.

   Plan and position top, side, front and rear views. These can be done freehand by tracing over the grid lines, or you can use a straight edge (triangle or ruler). Use the grid line to count the squares and check your dimensions. Sketching the cargo prior to delineation of your trailer will help verify the correctness of your dimensions and give you something to “wrap” your trailer around. Sketches of the cargo should be on a separate sheet of paper but of the same scale as the trailer drawing.

   Figure 1.6 is an example of a rough freehand sketch. If you have drawn the item to scale, the dimensions are not necessary but you may want to include them for reference. Once you have recorded a general idea of your proposed trailer, set it aside for the time being and move onto the next step. The details for your trailer will begin to fall into place as you gather more information.

   

   Figure 1.3. Two common scales used for trailer layouts and the points on the paper mu the various dimensions fall. A scale of 25:1 will handle 125″ on a 5″ length: ueramus. scale of 20:1 will handle only 100″ on a 5″ length. The planned length of your trailer il help you decide which scale is most appropriate for your project.