It seems the most common concern when purchasing a trailer is the material from which the trailer is made. Aluminum and steel are the main materials used in trailer construction. I am going to explore the differences a bit in this post. Mind you, this is intended to simply cover the major issues, just skims the surface of this topic, and is speaking in general terms to give you things to consider. Realize, there are ALWAYS exceptions. More information on the actual science, design, and manufacturing can be found in other sources.
Steel trailers have been around for a LOOOONG time. They are rugged, sturdy, heavy duty, and stand up to abuse. When it comes to livestock, particularly animals that may be a bit rowdy or rough, rugged is a good thing. I once witnessed an incident in a large steel trailer, in which multiple horses had been loaded. I’m not exactly sure what caused the accident, but somehow, the horse at the very front of the trailer collapsed, falling under the horse next to him. This caused the second horse to react, and he began violently stomping, bucking, and kicking at the horse underneath. All horses in the trailer were unloaded as quickly as possible, and all horses were OK in the end (minus a few scuffs on the front horse that had fallen). The trailer, however, didn’t show a single ding or mark from this rather violent, abusive incident. Likewise, I have seen both aluminum and steel trailers where horses have reared up and smacked their heads, usually leaving dents in the softer aluminum, but I don’t recall having ever seen a dent in the steel. That’s not to say it can’t happen, rather, I’m just trying to emphasize that steel is durable.
Steel is also a metal that is in plentiful supply and thus easier for manufacturers to acquire. It is easy to work with and easy to repair. For those reasons, steel trailers tend to be significantly less expensive than a similiar trailer made of aluminum. Because steel is always painted, trailers come in many color choices.
The weight of steel can be a downside. While there isn’t much that can be done, some manufacturers of stock-type trailers use steel piping for the walls rather than solid walls, while others just use lots of windows, all to decrease the weight a bit. At the same time, steel conducts heat much slower than aluminum, meaning animals can actually remain cooler in a steel trailer than in an aluminum one.
Another downside is rust. If it does get a dent from a horse kick, a scratch in the paint, or a little rock chip in that galvanized coating, the steel is more susceptible to rust. And man, can it rust fast! I have seen 10 year old steel trailers so rusted out, you have to wonder how the frame is still standing, let alone driving down the road full of cattle! At the same time, I have seen 20 year old trailers that are looking in really good condition, with just little bits of rust in strategic places, such as around bolt heads and wheel wells. What’s the difference? First of all, the quality of the steel and the paint and/or galvanizing job that is coating it (read the “Composite” section for more info on galvanizing). This is determined by the manufacturer. As a GENERAL rule, you get what you pay for. I have seen brand new steel trailers, matching the same specifications, but one is priced at $4,000 while another is priced at $7,000. Such a difference should be a red flag that causes you to further research the way the steel is coated and how durable that coating is. In the case of the $4,000 model I found, I liked it, but it turns out it was one of the most common trailer brands in my local repair shop, not only for structural issues, but also because the paint tended to chip and easily flake off, and the trailer would rust very quickly. The most important factor in dealing with rust issues, though, is prevention. First, look for a manufacturer that uses good painting and paint-drying technique. Some lesser manufacturers simply spray the paint on, while others use primers and have full, trailer sized “ovens” that heat and bond the paint more securely. They may also use multiple layers of paint. Rust is caused by moisture. A trailer should be cleaned, the urine hosed out, and the trailer dried thoroughly immediately after use. This includes the undercarriage and axles, which also tend to get hit with all the salts and contaminated water from the road. If you live in a humid area, you need to make sure any dents, dings, or chips in the paint are sanded and repainted as soon as possible. The trailer should be regularly washed, and maybe even waxed, to prevent oxidation, and to give you a chance to closely inspect it. This will go far in preventing rust.
Aluminum trailers have been around for a number of years, and are becoming increasingly popular. The advantages touted by fans of aluminum are the fact that aluminum does not rust and is very lightweight, allowing it to be towed by a smaller vehicle, and it has a higher re-sale value. Many people like the attractive silver color, which also eliminates issues with chipping, aging, or oxidation of paint. The aluminum itself will oxidize also, which, although unsightly, actually creates a protective barrier over the aluminum. There are some manufacturers now offering colored aluminum, which adds some variety. The major downside of aluminum is the expense involved and decreased durability potential of the frame. Many of these facts, however, are either widely exaggerated or not fully understood by buyers.
Weight is often the first consideration. In this modern day, there are many owners who want to haul just one or two horses, and desire to use their small SUV or 6-cylinder pickup. A small 2 horse, straight-load, basic trailer may weigh as little as 1800 lbs or so. A similiar model steel trailer, however, may weigh 2500-3000 lbs, which makes a big difference, and could require a larger tow vehicle. However, if you are looking for a bigger trailer, this benefit is greatly decreased. S spoke with an un-biased engineer, who formerly worked for Alcoa (world’s leading producer of aluminum), regarding using aluminum for the frame. He explained that one of the most widely used high-strength aluminum alloys is alloy 6061 with T6 temper. Pound for pound, 6061 can be stronger than some steels, but not as strong as others. The fact is, for any given aluminum alloy, there are higher-strength steels that outperform aluminum in strength-to-weight ratio. In layman’s terms, you could actually build a steel trailer that’s lighter than an aluminum trailer but it might cost you a pretty penny. He also pointed out that in order to properly use aluminum, the entire trailer would need to be redesigned to accomodate the differences in materials. Unfortunately, some trailer manufacturers may have taken their standard steel trailer design, and simply replaced the steel with aluminum (not a good idea). While there are exceptions, if they did it right, you would pay for the re-design process and the increased structural support. The vulnerability of aluminum would be the welded joints. Steel welds well but aluminum welds are difficult to do and require some significant overdesign to prevent cracking. In fact, our engineering expert, who used to work at Alcoa, explained that when working with aluminum that could withstand a stress of 35,000 lbs per square inch (psi), the joints and welded areas were designed to hold only 2,000 psi. That is a HUGE difference if you think about it! Another thing to consider is that the aluminum used in trailers is generally softer than their steel counterparts so a well-placed kick from a horse could significantly damage an upright support that would compromise the integrity of the trailer. In any case, the softness of the aluminum used (probably 6061) means that multiple or thicker layers of the aluminum must be used, particularly in the frame, in order to support the stresses of supporting the weight of the trailer and livestock, and the vibration stresses involved in travel (aluminum is more vulnerable to long-term vibration damage than steel). Longer trailers also often have tack or dressing areas and heavier-duty axles for hauling more livestock weight. My comparisons of different brands, and different trailers within the same brand have shown that the actual trailer weight of aluminum vs. steel only changes by about 800-1500 lbs. in trailers of 16 foot to 24 foot length. In this size range, chances are you would be using a tow vehicle capable of hauling up to 10,000-15,000 lbs or so anyway, in which case an aluminum trailer weight of 4200 lbs isn’t a big advantage over a steel trailer weight of 5000 lbs–especially if you consider that you would be paying a difference of roughly $5000 dollars more for the slightly lighter trailer. In fact, during our search for the right trailer, we discovered one top steel brand that used floor supports of angle iron on 16 inch centers. Right next to it was a similar model aluminum trailer with aluminum I-beam supports on 8 inch centers. Due to the extra reinforcement of the aluminum trailer, there was only a 200 lb difference between the two trailers!
A popular feature of aluminum is it’s resistance to rust. This is true, and can be very beneficial–especially in humid environments. HOWEVER, it does corrode, and some of the most corrosive liquids for aluminum are urine and salts (often found on roads at all times of year). Just as much preventative cleaning is required for aluminum as for steel in order to prevent the corrosion. Further, a factor usually overlooked with aluminum trailers is that the part of the trailer most susceptible to salts, urine, and moisture is the undercarriage. In most aluminum trailers, the axles and attached components are usually made of steel anyway, meaning you get no benefit from aluminum in this area. I have come across only one trailer manufacturer that makes all components of the undercarriage from aluminum, but I haven’t been able to figure out the intricacies of this fact, since aluminum is so soft. The durability and safety of this design would require a lot more research.
Another factor we discovered in our research was the quality of the aluminum itself. Different manufacturers use different sources for their aluminum. They melt it down and mold it in differing ways. If not done properly, the processing of the aluminum can cause weak “stress points.” These points are more prone to failure. While the average hauler may not notice minor issues with the frame, which is mostly hidden anyway, the repair shop owner I spoke with explained that certain brands of aluminum trailers have shown a consistent problem with “stress fractures,” particularly near joints and soldered areas. In fact, as it turns out, one of the most popular aluminum trailer brands, thanks to its famous high quality aluminum, recently changed suppliers. The new supplier also happens to be the supplier for the lesser brand that this repair shop regularly sees for stress fractures. While difficult to know for sure, I did find that pricing helps determine quality. I found a standard model of trailer from the lesser manufacturer to run about $13,000, while an identical model from a still well-built manufacturer was closer to $17,000. You pay for quality. Most of the time. I also found a similiar model from a well-known company going for $19,000, yet, according to the repair shop owner and my research, it is really just average.
Finally, a factor we never considered previously was the difficulty in repairing aluminum PROPERLY. Mind you, a number of folks take their trailer in for a repair that may require welding, and never think twice about it. However, all you have to do is ask a couple engineers or welders about it, and you will quickly discover that aluminum and steel must be repaired very differently to be done properly. Unfortunately, most trailer repair-men and welders have been using a welding technique intended for the heavier-duty and thicker steel since they started their craft. They tend to use the same technique on the thinner, weaker, softer aluminum. This can result in the aluminum developing weak areas around the repair. The fact that the aluminum trailer continues to hold up is likely due to the fact that the average trailer owner uses their (repaired) trailer relatively infrequently, loading it with horses that stand fairly still, thereby limiting the abuse.
Finally, there are trailers made of composite (2 or more) materials. The most commonly seen mix is a trailer with a steel frame and aluminum skin and roof. It seems this would be the best of both worlds, giving the trailer the stability and strength of steel, with the lighter and rust-resistant shell of aluminum. In fact, this is usually how manufacturers advertise such trailers. Some manufacturers use galvanized steel or “galvaneel,” which is steel coated with zinc. The difference is that “galvanized” essentially means the steel was hot-dipped in zinc, and then dried, forming a thin, paint-like coating that will eventually flake off under stress. “Galvaneeled,” on the other hand, is also steel hot-dipped in zinc, but then the zinc is actually baked on, forming a tight bond between the two metals. While it too will erode over time, it lasts much longer and is a much higher quality.
Other materials often seen are fiberglass and canvas, typically used on the roof of the trailer in order to reduce weight, reduce paint fading or oxidation by the sun, and to decrease price. Of course, such materials would never hold up under a trailer roll-over, but then, who plans to roll their trailer anyway?
I came across one manufacturer that has developed its own patented frame technology, which is a zinc alloy, advertised as having the strength of steel, but the weight of aluminum. My engineer husband laughed when I read that to him, as the quality, weight, and strength of both steel and aluminum vary so widely, that making such a broad statement is clearly an advertising tactic (which steel and aluminum are they comparing?). What many people don’t realize, however, is that two materials can function one way when they stand alone, but when either mixed into an alloy, or simply allowing them to contact each other, may cause them to function a totally different way. Consider an aluminum skin on a steel frame, for example. When these two metals contact each other, one becomes an anode and the other a cathode type reactor (search “galvanic corrosion”). When a corrosive liquid is introduced (ie urine or salt water), the aluminum rapidly disintegrates in a reaction that protects the steel. This is great for your steel frame, but terrible for an aluminum floor! Of course, this type of reaction can be prevented by inserting an insulating material between the two metals to prevent their touching. However, over time, this material would eventually deteriorate. You also couldn’t put any insulator between the actual weld and the metal piece it is supposed to be holding. We did find two manufacturers that do just this, and they use a high quality, long lasting insulator. However, you will pay for this extra precaution!
As you can see, every trailer material has its pros and cons. Fortunately, every trailer buyer has their personal needs and desires because every situation is different. I guess that variety is part of what makes the world go around (and keeps trailer manufacturers in business)! One thing is for sure, whichever trailer you decide is right for you, prevention is the key! Proper maintenance will help prevent all sorts of issues with your trailer, as well as improve re-sale value and trailer longevity. Keeping the trailer cleaned, rinsed, dry, and waxed (if applicable) will prevent rust and corrosion. If you have rubber mats, remove them regularly and clean them and the floor underneath. If you don’t remove them, at the least, place something under the mats after washing the tops, in order to raise them a bit and allow air to circulate, to ensure the floor underneath dries thoroughly. Don’t forget to rinse the undercarriage, belly, and wheel wells on occasion. To prevent brush and road-gravel damage to the outside, you can add a protective liner of some sort on the bottom 20 inches or so of the outer wall. Aluminum diamond-plating still seems to be the best buy. Spray-on liners are becoming popular, but still have a tendency to chip overtime when hit with gravel. Finally, between uses, store the trailer under some type of roofed shelter to protect it from the elements. If this is not possible, consider spending $100-$250 on a fabric, water repellent trailer cover. This helps shed some water, and protects from wind, blowing sand and debris, and sun exposure. When we used to live in the Mojave desert of southern California, this was our only option for protecting our trailer from the infamous desert winds and sand-storms. It worked quite well, actually. The cover completely disintegrated under the high element stress of the area after about a year, but our trailer still looked shiny and new! If a shelter is not an option, those covers can be worth every cent you pay for them!!