Bed Stiffener Alternative Solution???

Which bed divider do you have? Which one is this?

 

https://www.tacomaworld.com/threads/december-sale-bed-supports.695914/

 

Thanks. I’ll probably end up with a set from them or someone else.

 

The one in the picture as well as the one I own is the Toyota OEM cargo divider.

 

Thanks!

 

You're right. I realized that after responding. They limit bowing out but not the bed flexing inward. Anyway... Bed stiffeners are an easy install and I think we'll worth it.

 

Thanks again for the link. I went ahead an ordered a set of these. They look pretty stout and are priced very well. Plus, reading through the posts about these, he seems like a stand up guy.

 

And thanks again for everyone’s help and advice.

 

If one of the cargo rails is far enough back, it would prevent the bed rails from pulling in, and create something close to a square box with tension cross-bracing to add shear rigidity (limited by the pull-out strength of the buillt-in rail system since the D-rings on the deck attach to the mounting bolts into the frame and are definitely not a weak point). For the most part, that kind of shear rigidity isn't necessary in a truck bed, which is why truck beds haven't been significantly redesigned in many decades because most beds aren't subjected to much of the kind of torsional load that comes from doing off-axis trail driving with something like a RTT mounted on a bed rack or hard shell topper.

 

Did ya go with the stiffeners @tacoma_JT ? I have a cap on order and was thinking about these too - similarly fell down the rabbit hole - and am realizing that prob most people don't ever put these in with just a cap on their truck. Good insurance I guess, but we're not overloading our truck yet. Cheers. Adam

 

I did purchase some... but I since decided to go with a Softopper (installed last week) instead of bed rails and a RTT. So I don’t really have a pressing need for them now. I will probably try to sell them.

 

Got ya! I had the soft topper on my 2010 Tacoma for two years. I really liked it and came in super handy for the few yearly projects where it just got in the way. I'm holding off on the RTT for now but have ordered a Leer XR for my new truck. Good luck!

 

Why would a Tacoma need them and not other trucks. Why don’t we hear more about damaged bed from other owners. Is there any science or testing done to prove these are actually needed? Folks have carried camper shells with extra weight in many different ways and I am sure over loaded. Tacoma has been around for over 30 years. Plastic beds second gen and third gen. From 2021 to present 300k were sold. I wonder how many have damaged beds from not having bed stiffners. I have to say the creators of these are very smart to feed on our fears. This smells.

 

maybe even pull them in a little bit?

 

@Blisterinthesun reviving an OLD thread.

That would stress the weak points in the bed.

 

I'm sure it's more of a case by case situation than it is a universal solution, as people don't all use the trucks the same way.

There's not really any research, because not all tacoma owners are enthusiasts. I'd bet there's probably tons of trucks out there with damaged bedsides whose owners have no idea because they don't care, or don't stress the bedsides enough for it to completely fail.

ultimately, no one is forcing anyone to buy them. They give me peace of mine, so I have them. If you think they're a gimmick, don't buy em. Don't think anyone will say you have to have them, or that you're stupid for not buying them lol. Just that it might inhibit future/further damage

 

From what I've seen and understand, the people that have issues with their bedsides bowing out are the ones who have heavy shells on their trucks. More so the people who have shells with additional weight on top of them like RTTs for example. Think of a 5 gallon bucket on it's side with a stack of books on top; the sides will bow out. It's the constant weight over time that is going to flex the bedsides out and keep them out so that the material eventually adopts that position and doesn't return to it's original position when the weight is removed. If you were to take that stack of books off the bucket after a couple minutes, it would return to it's original shape; leave the weight on there for months or years however and it's gonna stay deformed.

In my mind, a little flexing is not a bad thing. It's the hard, rigid structures with zero give that end up getting damaged. If you put your bed bars on with an RTT and take your truck onto a trail, it is going to flex and deform a little as the truck moves, just as the frame of your truck will flex and deform a little, the key is that it isn't going to permanently deform, it has a certain level of elasticity and will bounce back so to speak as long as you're not doing anything too extreme. If you put those straps on, I would be more concerned with hitting a big bump and that rigid setup not giving at all and then you're looking at possibly damaging one of your anchor points, your ratchet straps, or your bed rails. I personally would prefer a little flexibility with the setup you are proposing. The guys and gals with shells and a bunch of added weight on top of it are the ones who should consider stiffeners to prevent the bedsides from spreading apart under that constant weight over time.

Just my $0.02

 

For the most part, I agree with you. No need for bed stiffeners if you aren't loading weight on your bed rails. They are handy for extra tie down points though, and I do love them for that. I ran an AT habitat on the bed rails, so consistently had 350+ pounds on them. Definitely not what they were built for. I've seen a good number of pics of cracks on here where the corner of the bed, like where the vertical part containing your taillights makes a 90 degree and goes under the plastic bed and to the opposite taillight (sorry, I didnt look for any, but could find some if you wanted).

 

The parts in bold are inaccurate in their entirety.

Every manufactured bedrack and every topper on the market has the ability to keep the weight of itself and what it's holding from causing the bed to splay outwards simply due to the weight sitting there on the bedsides. They have their own inherent rigidity/stiffness which does not splay the bedsides out. The weight of itself and its contents acts straight down towards the ground. This goes out the window if the bedrack is assembled incorrectly, or your topper is severely cracked, etc.

Movement (i.e. driving) is what causes the distortion of the bedsides.

Here is what I spent an hour writing for another bed stiffener thread. I have added bold to the parts that are more applicable to this thread.

Alright, I will attempt to shed some light on this topic as I see it brought up numerous times a year and I feel qualified to offer a sophisticated opinion on the matter.

I am a practicing Structural Engineer with a degree in Mechanical Engineering (meaning I understand dynamic motion, kinematics, kinetics, etc.) and another degree in Mathematics.

Alright, so let's start with the difference between static load and dynamic load.

Static load is stationary. This is the weight of all of your camping stuff if you placed it all on a scale and summed the weights. For explanatory purposes, let's say this is 500 lb. in total, 300 is stuff in the bed of the truck, secured to the bottom of the truck bed in various ways, and 200 lb. is your RTT and rack. Rack connection style (i.e. fully welded, or modular/bolted together) is not important, as we are analyzing the truck bed and not the rack. Either connection style (of all manufactured racks I have seen, someones DIY rack may not be designed properly) will perform the same.

Dynamic load is a static load under movement. Think of yourself standing on a scale, without moving, and seeing a displayed weight of 150 lbs. Now, to get off of the scale you decide to crouch down and jump off of the scale. At the moment of maximum force (when your body begins to accelerate from it's lowest position, assuming accel is constant throughout the jump) the scale reads 320 lbs (arbitrary number as it is a function of how hard you jump up). This 320 lb. is the dynamic load generated from a 150 lb. person through movement.

Ok, so now that we understand the fact that static loading can be modified to dynamic loading via motion/movement let's move on to the next topic.

The translation of forces. As an astute follower of Physics 101 you may say, "I know the weight of an object acts towards the center of the earth, which for all intents and purposes is perfectly vertical towards the ground" which is 100% accurate. But what is important to understand is what happens to purely vertical forces once they are resisted at a location that is not co-linear with their center line or neutral axis or center of mass. You see, when you're driving down a bumpy road with your RTT loaded onto your truck and you're causing your rear suspension to compress and elongate as you travel, your RTT is moving up and down. But due to the fact that it's center of mass is a distance truckbedwidth/2 from the sides of the truck bed and (truckbedheight + rackheight (to tents COM)) from the bed of the truck a portion of that vertical force is translated into lateral (side to side) force. This force is what ultimately damages your bedsides.

This is why rack support hardware that allows for the installation of a tonneau cover, i.e. the KB Voodoo rack in the video linked above, are inherently flawed. Flat plates are terrible in resisting bending forces caused by the lateral motion in this system. This is also why a flat plate system can easily support 1,000 lb while you and your family and your dog are sleeping in the tent at night, but the manufacturer imposes a weight limit for the flat plate system that is far below that (200 or 300 lb IIRC). The flat plates could never handle the dynamic forces caused by a static load of 1,000 lb, which we have demonstrated above as being much larger than 1,000 lb.

This takes us to our final topic for this post. Shape properties.

We have now left the RTT and tops of the bedsides alone and we are looking at the bottom inside corners of the bed near the tailgate, as this is the location where all of the lateral forces created by the dynamic motion of the static load are resolved/handled/dealt with.

There are a lot of things to think about here but a couple important ones are as follows:

Stress concentration factors (k factor): This is a factor that is a function of the shape and size of a discontinuity in a shape i.e. a 90 degree bend with a very small radius in the case of our truck beds. This situation has one of the highest k factors, second only to a perfectly square 90 degree angle with a radius of 0.

Distances: The bottom inside corners of the bed near the tailgate resist what are called 'moment forces'. These are forces that have units of force*length (or distance) (i.e. ft*lb or k*ft). These are not pressures btw, which features units of force per area. Now, moment forces are real things, but they need to be resolved into shear/tension/compression forces. And to do this we need to modify the units from force*length to simply force, as force is the units of shear/tension/compression (i.e. your body weight on a scale - 150 lb). To do this we need to divide force*length by length (of the same units (i.e. feet by feet or inches by inches). Based on simple math, if you divide a moment of say, 100 ft*lbs, by anything less than 1 ft, you end up with a shear/tension/compression (s/t/c from now on) force that is higher than 100 lbs. Dividing 100 ft*lbs by .5 ft results in a force of 200 lb. But, if you divide the moment force by anything larger than 1 ft, you end up with a force less than 100 lb, with the larger the distance, the lower the force (all the way to infinitely long with a force of 0 lb.)

Section Modulus: The easiest way to explain this is to think of a piece of flat steel or aluminum from your local hardware store. If you grab a 4 ft piece from the bin there and you hold it so the flat side is pointed towards the ceiling, you can easily bend it in your hands by rotating your hands from your palms being flat with the ground to your palms being parallel to each other. However, if you rotate the piece 90 degrees so that the skinny side points towards the ceiling and the flat side is towards your chest, all of a sudden the piece cannot be budged even a fraction of an inch. What happened? This is the function of the section modulus, which is a variable that determines a shapes ability to resists bending forces (Fb = M/S). For this example of a piece of steel/aluminum with a rectangular cross section, the section modulus (S) is calculated by the simple equation (b*h^3)/12 with b being the width and h being the height. A quick look at that equation shows you that the height of the section (in relation to the axis about which it is being bent) is much, much more important than it's width as the h term is cubed in this equation and it is located in the numerator of the equation.

So, what does all this crap mean?

What it means is, you need to reduce the stress concentration factor by increasing the radius of the discontinuity, you need to maximize distances away from the point of inflection and you need to be intelligent in the way you design the bracket by using the inherent strength of properly designed/chosen shapes.

This is why, as posted above, a bracket with a small angled piece of steel near the corner is better than the bed itself, as it modifies the k factor, and increases the distance between point of inflection and the resolution of the forces (the small piece of angled steel). Also, the flat plate approximately 1/16" above the lowest bolt does little to nothing to reinforce the bed corner and can be omitted from future designs as it is a waste of material and weight. However, while this bracket is better than nothing, it pales in comparison to a more mainstream stiffener, as these stiffeners takes advantage of the section modulus of a more intelligent shape (i.e. the plate that runs to the top and side of the plates parallel to the bed floor and wall).

So, with all that said, what is my verdict?

Get bed stiffeners if you have a RTT that you mount on a rack that places the COM of the tent/rack combo anywhere above the floor of the truck bed. You see, we ignored the 300 lbs of stuff strapped to the floor of the bed, as all of its lateral forces are resisted co-planar to the floor of the truck, and thus do not impart any moment forces on the corners of the bed (which is what we were concerned about in this discussion). Only a weight a distance above the floor can do that, with the higher the location of the same weight resulting in higher forces.

Now, with that said, I have not performed an analysis of this system to determine the moment forces being resisted at the bed corners, and therefore cannot determine the appropriate size of a bed stiffener to mitigate any potential damage. Until someone pays me to do that I can't say that the smaller angled homemade bracket above does anything less than what is required relative to the more mainstream stiffeners. But I can tell you, based off of first principles in engineering, that the more mainstream mounts are a much better choice for this situation at this time.

This is not the end all be all analysis of this situation, but it is certainly a well thought out one presented by an individual with the necessary credentials to understand the phenomena we are witnessing.

Alright, that took an hour. Let me know if you have any questions.

 

The one case I've seen where the back of a tacoma bed flexed out was a truck with a bed rack that had a RTT and other gear mounted to it which was used for fairly heavy technical off-road trails and rock crawling. Severe off-axis terrain combined with significant weight mounted up high produces a kind of loading which is very uncommon and might not be anticipated by the design engineers. A bed rack vs a hard topper will also transfer that load into the bed rials very differently since the topper has continuous contact over the lenght of the bed rail where the bed rack will concentrate load transfer at the corners (even if there's a small strip or angle of metal connecting the front and rear legs of the rack together, the vertical load transfer will concentrate at the legs. Flexing while also climbing will put a lot of twisting and shearing into the back corners of the bed, and the tailgate latching isn't well suited to really help carry that kind of loading.

In the case I saw, there was also a broken weld in the rack, but it's almost impossible to know afterward whether the rack or the bed had issues first, or if both flexed out too far at the same time.