Even if you’ve no desire to live in one, you must admit, Airstream trailers look cool. Aerodynamic styling is part of the appeal, but so too is the bright aluminum bodywork. It’s said that 70% of all Airstream trailers ever built are still on the road, and while there’s probably no way to verify that claim it doesn’t seem unreasonable. We know aluminum doesn’t rust like steel, and let’s be honest, someone who spends six figures on an Airstream is probably going to look after it!
Of course, you don’t have to buy an Airstream to get an aluminum trailer. Aluminum is used for trailers of all types, including horse trailers and general utility trailers. It’s known for being lightweight and rust-resistant, but when used for a trailer are you trading durability for low mass? Here’s a comparison of aluminum versus steel for decreasing trailer weight.
Grades, Strength and Specific Strength of Aluminum and Steel
Aluminum and steel are both alloys. They’re made by mixing the base material – aluminum or iron – with other elements. Each composition produces a specific grade and both are produced in grades to suit various applications. There’s not enought space here to go into all the details, but lets just say that, going forward we’re talking about the two metals in general terms rather than referencing specific compositions.
Alloy composition determines properties like strength and hardness. Strength is defined in various ways such as Ultimate Tensile Strength, (UTS) and shear strength, but it’s probably ‘2% yield strength’ that best reflects useability. This is the load under which the metal transitions from elastic to plastic deformation. Whichever measure you look at, steel comes out on top, but this does need qualifying.
The point missing from this discussion so far is Specific Strength. That’s the strength per pound and it’s where aluminum turns the tables on steel. That’s because while steel is stronger it’s also a lot heavier. A cubic foot of aluminum, (which is a pretty massive block of metal,) would weigh about 169 pounds. The same volume of steel will tip the scales at 490 pounds. What this means is that the specific strength of aluminum is higher than that of steel. In other words you need only a little more aluminum to fabricate a shape with comparable strength to one made from steel.
Other Properties Relevant to Trailers
Strength is really about load-carrying ability, but there’s more to choosing a trailer material than that. Elastic behavior and fatigue strength are other considerations, and ones where aluminum comes out ahead.
In simple terms, it takes more force to bend a piece of steel than a piece of aluminum because it’s stronger. Aluminum however has better elastic behavior, meaning it springs back to it’s original shape while steel takes on a permanent deformation. In addition, being harder, steel is also more brittle. Subject it to a cyclic load, as a trailer might see, and it will start cracking sooner than aluminum. And in one other interesting twist, unlike steel aluminum actually gets stronger at low temperatures.
Aluminum for Light(er) Weight Trailers
Whatever type of trailer you buy, it’s purpose is to haul stuff. A lighter trailer is advantageous for three reasons. First, given that your tow vehicle has a maximum weight it can pull, a lighter trailer means more payload. Second, maybe you can get away with a smaller tow vehicle when a lightweight trailer reduces the total weight you’re pulling. And third, by reducing the total mass you’re towing you’ll improve your fuel consumption.
In a trailer aluminum works for both the load-bearing structure and the panels. Load-bearing members are almost always extruded into “I” or box sections which gives them a lot of strength while panels can be very thin to save on weight.
A couple of points to note on this are:
- Panels and structural components are made from different grades of aluminum. This complicates the welding, as detailed in our TikiTalk post, “Trailer and Truck Body Manufacturing with 5356 Aluminum Filler.”
- It’s rarely a good idea to clad a steel structure with aluminum panels as this creates a risk of galvanic corrosion. (If you want to get really lightweight, consider GFRP, as discussed in “Lightweight Comparison: Steel vs. Aluminum vs. GFRP.”)
So having been through all the points about material properties, let’s turn to what you really want to know: how much does aluminum decrease trailer weight when compared with steel?
Honestly, it depends on the skill, creativity and materials know-how of the engineer. However, you’re looking at a 10 to 15% reduction in total weight. (Remember that you still need brakes, bearings, wheels and so on, so there are no, or very little, weight savings to be had in those areas.) If you want to get more specific, talk to your trailer fabricator.
After weight this is probably the second thing you want to know about. Here we’re going to make the argument that you should consider total lifetime cost. Yes, we understand that when you read that it means an aluminum trailer costs more than one made from steel. Aluminum does cost 3.5 times as much per pound as steel, but you are using less of it, so the premium for aluminum isn’t that great.
However, stay with us while we explain the total lifetime cost perspective. Like steel, exposed aluminum oxidizes. Unlike steel though, aluminum doesn’t disintegrate in a cloud of brown flakes. In fact the oxide layer on the skin of a piece of aluminum is self-healing: scratch it and it just forms a new oxide layer. As a result, you don’t need to paint an aluminum trailer every few years. That’s a saving right there.
Another saving hits your pocketbook when you buy gas. Being as though aluminum trailers weigh less than steel ones, you’re going to save money by using less of it.
In addition, the aluminum trailer is going to last much, much longer. Maybe one aluminum trailer could last as long as two or even three made from steel. (We don’t know that for sure, but based on Airstream trailer longevity we think it’s a fair assumption.)
So when it comes to cost, the bottom line is this: an aluminum trailer will cost more initially, but thanks to low weight and long life it should more than pay for itself.
Not Everyone’s Concerned About Weight
If you were wondering about aluminum versus steel trailer weight, hopefully we’ve settled that for you. Aluminum. But what about the weight of an Airstream trailer? Well that’s gong to depend on how you fit yours out, and some people like them pretty fancy. It’s probably fair to say then, this is one aluminum trailer where no one worries much about the weight. They do look really cool though.