|
Trailer Design
for Versatility
Links for further reading:
1. Introduction.
2. Trailer Strength.
3. Stability.
4. Versatility.
Choosing the Right
Utility Trailer.
Trailer Towing Tips.
More Articles . . . |
|
|
|
Page 4: Options for Versatility
A look at Trailer Options for Greater Utility
Versatility is a broad and sometimes vague area to define. In the context of a utility trailer, the necessary
(or even desired) options that make the trailer versatile are so highly dependent on the intended use. However,
when you have a need, choosing the right options will certainly effect how much you like (and use) the trailer.
The areas below are intended as items to consider. The desirability and usefulness will depend on
individual preferences and the given application.
| Size Considerations: |
|
Trailer Size (and size related options) are the obvious first choices. Most of these
options are really fundamental decisions made at the start and are not usually variable.
There are several Capacity Options available. Typical sizes are 1000#, 2000#, 3500#, 5200#,
6000# and multiples of these.
Next are choices for the Number of Axles. Do you choose a single axle? Or double?
Or maybe even triple? It all depends on the need.
Overall Trailer Size will also depend on the need. (See your local restrictions on length, height and width if
you are considering long, high or wide trailers.) |
|
Suspension Type is sometimes overlooked as an option because leaf springs are so common. Actually, the
typical leaf spring with pivots is the most common, but slipper type leafs are also popular -- especially in high
capacity and multi-axle trailers. Rubber torsion suspensions are gaining popularity on light duty trailers
because of compactness.
| Other types of suspensions seen once in a while are the coil spring (right) or latitude leaf spring (below) shown
in these 2 pictures. |
 |
 |
| Thoughts on Suspension: |
|
Each suspension type has advantages and disadvantages. When considering suspension, here are a few things to consider:
Single Axle Leaf springs with dual eyes (one spring set per side):
- Advantages: These are the most common, and probably the most practical. They minimize stress on the frame because they apply a simple
vertical load at 4 distributed points on the frame. They are easy to set-up so the axle position is correct. They are attached with through bolts for
simple constraints of the system, and the back shackle is a simple, dynamically stable method of taking up spring deflection.
- Disadvantages: include size, weight, and package constraints (they can take a lot of room under the trailer and limit how low the bed can be made.
Multiple Axle Leaf Springs
- Advantages: Like above, but for multiple axles, these springs distribute a simple load fairly well to several points on the frame.
These can be made to load share quite well with a rocker link (usually included).
- Disadvantages: Like above, these take a lot of space and pose limitations on bed height. Different variations exist, but typically for load
sharing the rear axle is not as well constrained as the front, so these tend to be somewhat less stable than the simple single axle.
Slipper Style Leaf Springs
- Advantages: There are some packaging advantages, though not too much. These are not used very often on single axles because they don't really
have many advantages over the pivot style, but for multiple axles, they make mounting and load distribution much easier -- particularly with 3 or more axles.
In multiple axle applications, especially for high capacity, these are very popular because they load share well, and have stability advantages.
- Disadvantages: These systems can be noisy on rough roads because there is a loose spring end that can move. They can also create a lot of
wear on the metal parts that rub together, so some accommodation for that should be made.
Torsion Axles
- Advantages: These can be very compact and allow additional freedoms in designing the trailer. The elastomer also gives some natural damping
to the "bumps" in the road. They are also very nice because single sided units make for an independent suspension. Torsion axles can be a good choice
for light duty trailers -- BUT ONLY if the frame is designed for the added stresses.
- Disadvantages: While it is true that they make torsion axles for larger capacities, we do not recommend them for the following reasons:
First, the loading of the torsion axle to the frame is more complex and localized on the frame. This adds stress (a lot) over simple the leaf springs described above.
Second, Loading to the frame can be complex -- especially when individual units are used so there are moments in 2 directions along with vertical loads.
Third, Torsion axles don't load share in multiple axle configurations. This means as a trailer is pulled over a bump, the one axle takes far more of the load
than the other -- which means one could overload while the other is hardly loaded.
Finally, because the "spring" is an elastomer, it has a limited life. Over time (years), the elastomer will gradually harden and crack.
Other Suspension Types like transverse leafs and coil springs (shown above) are not widely used because of their limitations. Coils can be
the most compliant (soft) and can have the most travel, but they usually require more complex attachment (like trailing arms) and can be space inefficient (vertically).
Shock Absorbers. I am frequently asked about shock absorbers on trailers. Most trailers do not have them. In general, if you
wish to have a cushioned ride, shocks are great. If a little bouncing is not a bother to the load, shocks are not necessary.
Note that shocks will not reduce the bouncing of a nearly empty trailer. Shocks work between the axle and the frame but the bouncing of a nearly empty
trailer is really the tires (like bouncing a basketball). To avoid the bouncing, reduce tire pressure when the trailer is empty -- maybe as low as 15 psi or even 10 psi.
|
| Recommendations: |
|
The key is using the right suspension for the application. This article cannot cover every possibility, so use the knowledge and choose a suspension that best fits the need.
A first choice is usually Single Axle Leaf springs. Why Single Axle?
- Tires are pretty good these days so extra tires to compensate for a flat is not a good reason for multiple axles.
- Single axle applications are less expensive.
- Single axle trailers require less maintenance.
- Single axle trailers are easier to maneuver.
- Single axle trailers are more efficient to pull so fuel efficiency is better for the tow vehicle.
For multiple axle applications I usually recommend the Slipper Style Leaf Springs for stability. Use multiple axles when:
- The loads are large -- too much for a standard single axles.
- The trailer is quite long (with large loads) such that stresses are a factor in choosing multiple axles. However, it is usually cheaper and easier to strengthen a long frame
than to add axles, so load is really the controlling factor.
Choose Torsion Axles when the load is particularly light, and/or when the ride needs to be particularly cushy. If you use them, choose a full length axle rather than 2 short ends.
The stresses will be less and the wheels will align.&nbps; ... Some say to use Torsion Axles for a low bed height, but I say, unless the load is light (< 1000 lbs.),
sacrifice a bit on bed height in favor of a more robust suspension.
Note: I know some will disagree. That is just fine. There are lots of great trailers out there that don't fit these recommendations.
And that is just what these are: Recommendations -- from my experience and point of view.
|
|
|
Some functional options for Brakes (needed or not?) including types and methods of actuation (electric,
hydraulic, applied or surge) are discussed in detail in the Stability section.
Breakaway brake activation can be another nice safety feature. Basically these devises activate the
trailer brakes if the breakaway connection comes disconnected. These are used mostly in more industrial and
heavy applications and require additional setup, configuration and maintenance.
Options for Wheels & Tires abound. Trailer specific wheels and tires are available for most applications,
however, automotive components offer some nice benefits. From a functional standpoint, automotive tires offer a
better ride and wider availability. Then for aesthetics, automotive components offer a whole world of options.
Like with cars, wheels can make the look, so if you want to go in style, get the nice wheels. Just be sure the
specs (load, speed, size) match your intended use.
A Spare Tire. Do you need one? If so, where should it be stored? The picture at right shows a
good idea as a place to keep the spare. Not only is it out of the way, but it's convenient to check the tire pressure.
| How important is a spare tire? |
|
Perhaps a better question is how often are spare tires used?
The answers to these questions may be best attained with an assessment of the trailer use. If the trailer is
rarely used, or stored in the sun where dry-rot can be an issue, it might be really important to have a spare. On
the other hand, if you carefully inspect the trailer before use, keep the tires in good shape and have a good road-side
assistance program, a spare may not be needed.
If it's possible in your circumstance, a nice idea for efficiency is to have the wheels and tires of the
trailer match those of the tow vehicle. That way, if there is a flat, the vehicle spare will accomplish the task
for any of the wheels.
From a personal standpoint, in all the years I've pulled a trailer, I've only needed a spare once,
and it was the same size as the tow vehicle. I had 2 spares, and wondered why? |
|
Adjustable Height Hitch |
The Type of Hitch used to pull your load is certainly an option. Normally it's a given with a
particular trailer as to whether it's a bumper type hitch or a goose neck or a 5th wheel -- though I have seen
some interesting conversions.
In the realm of bumper type hitches, there is optional equipment to help stabilize the trailer with respect to
the load. Load-Distributing Hitches are a great thing for this. Dampers between the trailer and tow
vehicle are also available, but usually if one is needed, there are other more serious issues with stability.
(See the Trailer Stability page for more information.)
Tongue Jack and Safety Chains |
The option for a tongue jack and whether it has a wheel or not and whether it telescopes or not.
From a functional standpoint, the size of a tongue jack wheel will determine how easily the trailer can be moved
(off the hitch) on concrete, gravel and/or dirt (or muddy) surfaces. For trailers to be stored on dirt
surfaces, a larger tongue jack wheel may be desired.
Safety chains are required in most places and are a very good idea. The chains (and chain attachment
points on both the trailer and the tow vehicle) must be sized appropriately for the trailer. Obviously a small,
light duty trailer needs far less in safety chain than a Caterpillar hauling monster.
Sides (or not) are an obvious variation. They come in all different sizes and configurations.
Think about your intended use, then choose sides or not; make the sides permanent or removable; choose solid sides
or perhaps slatted, tall or short.
For the creative, when remodeling a trailer, the bed and sides can be extended beyond the wheels as shown in the
picture on the left. Just be careful then in the loading and load distribution.
If you choose sides, you may also want a Trailer Top. The top can be canvas, or hard; it may be permanent
or removable. A top may lift to gain access or it may be stationary.
One item of particular importance to consider with a top is the weather. What will it carry?
Is water an issue? Where and how will the trailer be stored?
That brings up the next item -- Fenders. There are all sorts of fenders available from stamped steel to
plastic, fiberglass or wood. They come square, round or as pasture fenders. Mostly they do the same job, so
looks and taste are the big reasons for consideration. Also, your state or province may regulate the need for fenders.
Another popular option is ramps. Sometimes the ramp is really the tailgate that folds down, sometimes
they are purpose built for motorcycles or ATV's, or perhaps a store under variety like on some of our trailers.
Let your needs dictate the type of ramp.
A good usability option that is often overlooked at the time of purchase is that of tie-down points.
Tie-down points are especially important with open utility trailers. Sometimes the tie points are part of the
frame, sometimes attached to the sides. Examine tie points to be sure they are adequate, accessible and not in
the way. (I've wracked my knee many times against tie points welded in an exposed location.)
Round bars on the trailer sides make great tie points all along.
Tie points should be located in convenient locations based on the intended loads, or (as in most of our designs)
have adjustable positioning. Dedicated tie points for specific loads (like motorcycles or ATV's) must be strong
enough for the given application.
Added Storage compartments like the tongue box in the picture can make a nice addition to a trailer. As
with this box, a nice weather tight (and/or secure) place to put tools, tie-downs and other items can be very useful.
Boxes such as this can also be added to the sides just in front or behind the wheels, or just under the bed. It all
depends on the specific application, and on your needs.
Finally, every trailer designer has some nifty options available with their trailers. Some we have done
are the movable (adjustable) axle, and the removable tongue. The movable axle allows the trailer to be flexible to
loading needs. The removable tongue allows the trailer to be stored in a much tighter space.
Summary:
Options for a given trailer are primarily a matter of taste and need - and perhaps a matter of what things can be
accommodated in a particular design. Several options for both safety and utility are listed here for reference
and consideration.
 Go to "Choosing the Right Utility Trailer"
|
