Prior to starting new plans, we do research to understand the landscape, then look for opportunity to improve and make a better product. That is certainly the case with our upcoming Equipment Transport Trailer & Car Hauler design. * New plans are coming soon. *– (Photo above from M&G Trailer.)
There are a lot of Car Hauler design ideas and configurations. So, over the past while we have studied them, thinking about the good ideas, and about areas to improve. Of course, every trailer has a target purpose, so things do not always compare. Yet, in this general category, there are some key similarities.
For this article I want to share JUST ONE finding that has me both confused, and a little shocked. With the perspective of trailer frame failures, I always look at the materials and think about the Engineering. From our finding about Car Hauler design, here are some things to consider.
Material Choice
In the Car Hauler trailer / Equipment Transport world, it is very common to identify (and brag) about the material size for the main beams. Names like H6X 6″ CHANNEL BUGGY HAULER, or the 6″ Channel Equipment Tilt (T6) are two examples. I like the concept, but for many people the name is a bit deceiving – because it implies strength.
Along that same line, I like the trend in the trailer industry to be more open about materials in general. Many websites and videos talk about material and spacing, for things like the frame, cross members, the tail, deck, etc.. I think this is great.
But, there is a catch. Since we do not know what is actually Strong Enough, statements about materials pose an interesting deception. What if the names and claims are smoke and mirrors?
Are they are actually bragging about how weak the trailer is? That will not help our new Car Hauler Design.
Car Hauler Design & Loading
Here is what I mean. We will look at some capacity claims, then at the load. After creating a simple CAD model to represent the situation, I ran some numbers. My past experience says the large trailer manufacturers do a lot of bragging – without backing it up – so this is worth a check.
I have a particular interest in the tilt top car hauler design. I think they offer excellent functionality. However, this car hauler design has some fun challenges.
One challenge is holding the entire load on a center pivot. But it is more than that. The load is a car (or jeep, or truck, or tractor), which means the load contacts the trailer at only 4 points – the 4 wheels. And, the 4 points are a distance apart.
For the sake of argument, let’s use the dimensions of a pickup truck or large SUV. The wheelbase of a Ford F-150 SuperCrew® 4×4 is 157.2″. Weight is right around 5000 lbs. To compare, a Chevy Suburban has a wheelbase of 134.1″ and a weight of ~5700 lbs. Other large vehicles are similar.
If you had one, would you put it on a 7,000 lbs capacity trailer? A 5000 lbs vehicle would probably be near the limit (because the actual vehicle will weight more with fuel in the tank, a driver and perhaps some other stuff in it). For the Suburban or a larger vehicle, you would really need a 10,000 lbs trailer.
While most 7,000 lbs Car Hauler trailers brag 5″ Channel in the design, some go as small as 4″ Channel. The 10,000 lbs trailers are a mix, but most 14,000 lbs trailers brag 6″ Channel. Here is what I found.
Second Guessing Their Designs
The analysis model is a simple tilt deck. For simplicity, we are examining only the Tilt Deck, not the whole trailer.
While crossmembers are important on the actual trailer, once the vehicle is on it, only the cross members immediately under the wheels hold the load. For these analysis images, crossmembers and other components are NOT shown. A pivot bar is shown.
We are evaluating a transitional condition, because it is the point of load balance. Since this is a broad look, we acknowledge many minor factors, but we will not analyze them. Admittedly, for driving, the load is forward of the pivot for proper tongue load. That can reduce stress by 15% or so, static, but it is also subject to driving dynamics like bumps and potholes. That is a different analysis.
We will compare 3 vehicles. While these numbers are not exact, they do represent typical loading for a car hauler design trailer.
- An F-150 with a 157.2″ wheelbase at 5000 lbs.;
- A Suburban with a wheelbase of 134.1″ and a weight of 5700 lbs.;
- Just for grins, a Porsche 911 with a wheelbase at 97.6″ at 3800 lbs.
Results
First, this is the result with the Porsche 911 on a trailer with 4″ C-Channel for the main beams.
That seems reasonable. Replacing the Porsche with the F-150 — 5000 lbs at 157.2″ — we get this result for the trailer with 4″ C-Channel main beams.
If the trailer is 7000 lbs capacity and it weighs less than 2000 lbs, then both of the above are within the load specs. However, the trailer frame would certainly fail with the F-150. From this analysis, even as simplistic as it is, I would NEVER have a car hauler design with a 4″ C-Channel frame. Even with a double beam like in the image at the very top of the page.
(The top photo is an aluminum car hauler design, so it is a little different. I am not seeing the double beam design in most.)
Reading the Results
Now, we can take a minute and explain the graphics. First, the analysis setup is the image above with the tilt frame all in gray. Loading. The purple arrows pointing down are the location of the 4 wheels contacting the trailer deck. They represent the vehicle on the deck. Green arrows show the pivot axis. It is a 16 ft deck, but that does not really matter because the wheelbase is less, so we are not using the ends.
Wheel placement is not perfectly accurate since it assumes a 50%-50% split for load front and back. However, the beam loading (moment) is the same near the pivot at the balance point even if the actual vehicle is 60%-40% or some other number. Please remember, this is simplified to see the concepts, it is not for exact results.
Colors. The scale at the right shows a bunch of colors. They represent stress levels in the frame. Blue is near Zero stress, and Red is at the design stress of the material. (A36, rating at 36,000 psi.) The Bright Pink shows areas that exceed the material strength. That means failure. Sure, actual materials can be a little stronger, but it varies from batch to batch, so we must design under the minimum. Read this article about material and safety factors.
One more important point. This analysis is Static (non-moving). In practice, we almost never have true static loads. While it is nice for simplicity, trailers are all about dynamics with bumps, potholes, and dips. The car on the trailer will jostle up and down which momentarily increases load. For example, read about bending the tongue on this trailer. We compensate by designing with safety factors because we cannot possibly guess all the conditions it will experience.
Exploring Other Beam Options
What happens when we change our theoretical car hauler design to 5″ Channel? This is the result with 5000 lbs at 157.2″ on 5″ C-Channel.
For the 5000 lb. pickup, this is a marginal car hauler design. According to these results, it is just below the failure threshold. (Note the Max stress.) So, this is possible, but not on a rough road.
The Suburban is heavier, but shorter, so we will try it also on 5″ C-Channel.
For all practical purposes, the stress is the same. That shows us that wheelbase makes a big difference. The lighter vehicle with a longer wheelbase results in nearly the same car hauler design stress.
Next, we will change the frame to 6″ C-Channel. This first image is, again, the 5000 lb F-150.
This 2nd image is the 5700 lb Suburban.
Again, the results are nearly the same for the 2 vehicles. Notice that the highest stress is now about half the material strength. This is a big difference from 5″ to 6″ channel.
We had to go to 6″ Channel to find something acceptable for these vehicles. Acceptable, to me, means not near the limit of failure. BUT, on most trailers the 6″ Channel does not appear until the 14,000 lbs trailers. Hmmmm.
14,000 Lbs Car Hauler Design
We will take it one more step. If a 14K Car Hauler weighs something less than 4000 lbs, then we can put a 10,000 tractor on it. Right? Let’s see what happens. Here is the 10,000 lbs tractor on a 6″ C-Channel tilt deck. Wheelbase is 12 feet. What do we see?
Oops. The analysis shows the 3″ C-Channel cross bars fail. That is what we have in the CAD model because that is what the trailer manufacturers say they use. OK, we will give them the benefit of the doubt. Most large vehicles will have a wheel stance that will put at least part of the wheel on the main beam instead of completely on the cross member as in our model.
Well, for the sake of simplicity, we will change to 4″ crossmembers and rerun the analysis.
This shows the 14,000 lbs car hauler design is right on the limit if you actually put 10,000 lbs on it. Over the limit, technically. If we are lucky and this batch of steel is 3% stronger than the minimum, then it lives? If the wheelbase is actually longer, the beams will fail. Ouch.
Analysis Summary
We ran a lot of tests with fun images, but what does it all mean?
Basically, when comparing what trailer manufacturers are saying, when we put a these specific vehicles on, the tilt bed is either at the limit, or ready to fail. All of these are beyond the design limits I am comfortable with.
Now in fairness, this is a simple analysis with some hand-waving. The analysis does not take into account extra structure that is present on some trailers. Some manufacturers make accommodations for more of this load, but it is not as complete as I would like to see.
Also, on the practical side, once the vehicle is on the trailer, it will move forward, past the tilt point. This will reduce the distance to the overhanging back load. However, no matter how you justify it, these numbers are painfully close to disaster.
Another Way To Look At Car Hauler Design
If we do the analysis again, this time we use an evenly distributed load, we see something entirely different. Of course, this is unrealistic for a car hauler design, but we will go with it for educational purposes.
These look much better. Maybe that is how big trailer manufacturers design? But, the data is irrelevant, because that is not how a vehicle sets. Compare this to the F-150 on 5″ C-Channel frame. The truck puts weight in 4 locations. – I do not know what they do, but it is fun to experiment. If load ratings come from analysis like this, it is a problem for something sold as a “Car Hauler” design.
One conflict for trailer makers is material choice. They want a light trailer to save money, so they go (beyond?) the limits. But what about failures? Just search “Bent Trailer Frame” on Google or YouTube. You will find them. Unfortunately, most people blame themselves, rather than a weak design.
From a personal note, I wish manufacturers would make robust trailers. Unfortunately, in my career, but I see failures. People contact me about them, and I make money consulting to find a fix. That is not how I want to make money. I prefer to work with happy situations rather than stressful ones. Perhaps that makes me skeptical.
Anyway, you get the benefit from experience with plans here at Mechanical Elements. We do the full engineering, so build one that will perform.
Of course, building is not for everyone. If you are buying, get it one weight class heavier than you need. Then, label it down.
Examining Trailer Length
Another trend I see too often for Car Hauler design and Equipment Transport trailers is length choices. I think it is wonderful to offer the various lengths, but it is not what it seems. As we saw above, distance between the load points matters – a lot. So, a chart like this showing trailers ranging in length from 16′ to 24′ (50% more length) using the same material is a little scary.
Of course, capacity is the same, and the longer trailer obviously weighs more, so the load you can put on it is less. And, it has the ability to spread out more. But, if you load something on the front (like a pallet of bricks), then you need to push the skid loader back for proper tongue weight. That is opposite what we said above. That is why, 50% longer with the same material is kind of scary.
The above analysis we did is based on a 16′ tilt deck. What happens when you put 2 Jeeps on a 24 footer?
What Are We Learning?
The above quick analysis tells me our new car hauler design must consider the real loads. Failures in the field, and issues with weak trailers (on YouTube and in Forums like this one) tell me I am NOT wrong.
There are a lot of these trailers around, and they have a long history, so can it be that bad? Certainly, we will not argue with historical success, but I also cannot ignore the “so close to the edge” engineering. I think we are learning once again about opting for cost saving instead of good quality. They sure talk about quality, but I am not seeing it where it counts.
If you have a failure, a true warranty claim will they deny it? I see that in videos and forums. So, are we learning the wrong things? Are we learning again: buyer beware?
There is a statistical element too. I would like to know if it is real, but I wonder how much the manufacturers look at numbers. Do they think a certain number of failures are OK to justify lower cost? It is hard to say.
Anyway, after doing the analysis above, I will not be pushing the limits of those trailers. For our new car hauler design, we are setting (and meeting) appropriate trailer design goals.
How Would I Design a Car Hauler?
OK, I am blabbing pretty negative in these last few sections. It is always easier to critique than to create, so you might say “Hey, put your money where your mouth is!”
Stay tuned, because we are answering the questions with complete plans you can build. The first is a fixed deck at 20′, at 10,400 lbs. More Car Hauler Trailer designs are in process – made for DIY – with full engineering. Hang tight. Tilt Decks will come in a few months. (This is how we make the plans.) And, you can see all our Car Hauler Design Trailers on the Plans Catalog Page.
There are a lot of things I really like about the trailers in the research we did. Some features we will include, some not, some will be in the plans as an option. While some features are similar to existing trailers, we are definitely putting our spin on them. Especially when it comes to strength. Our car hauler design(s) are different, and stronger than what we see from the big boys. Here is the article on Car Trailer Philosophy.
UPDATE: The First Tilt Deck trailer plans are now available as a 7×21 Gravity Tilt Car Hauler / Equipment Transport. They are ready for you to build. While it all sounds so simple, anything with moving parts is more complex than a fixed deck trailer, so these new tilt deck trailer plans include a lot more pages – both in the drawings and in the instructions. Download your copy today.
Watch the Trailers Section of the Mechanical Elements Plans Store. More Car hauler design(s) are coming.
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