Anyones else have their bed crack like this ?

Definitely a good idea.

No, I would not drill the holes. The bed stiffeners will be far more supportive than the factory setup.

I wrote up a whole write-up on the benefits of bed stiffeners, from an engineers perspective. I need to find it, turn it into a white paper, and put it out for the community.

 

@snowsk8air2 was the fabricator for Wills rear (and front) bumper. I am not sure of his schedule, but it doesn't hurt to ask.

 

Thank you sir!

I should’ve installed the stiffeners when I got my RTT and bed rack. Oh well, lesson learned.

This whole time I honestly thought that stiffeners were a gimmick. I was very wrong.

 

Here's what I wrote in another thread quite some time ago (not every reference will be applicable in this new 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 lbs in total, 300 is stuff in the bed of the truck, secured to the bottom of the truck bed in various ways, and 200 lbs 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 lbs 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.

 

Great info, thanks!

 

Link to thread? Interested in what sparked this response.

 

Fifty years ago, Toyota pickups had a "cam over rear tailgate latch" on both sides.

The beds were single-wall, dented easily, and super lightweight. That cam over lock helped stiffen it going down the road, but people wanted a one-hand opening (center latch).

When I first got my truck, I noticed just easily pulling on the side widened the tailgate gap! Oops, seems funny to remember my 1971 truck.

A random photo reminds people what we old gray beards are rambling about. Drum brakes all the way around, 60 hp, and took about a minute to get up to 60 mph. I got about 25 mpg, but was worn out after a three-hour drive!

 

I simply "slotted" my mat for where the angle iron came up through. Didn't trim any off.
There is a loss of width. Maybe two inches. ?? But I'm living with it.

 

It would be worth the five minutes it takes to stop drill the crack.

 

Hmm it’s not gonna make things worse without the bed stiffeners when I go out this weekend?

 

Drill the hole and throw a ratchet strap across the top of the bed as close to the tailgate as possible until stiffeners arrive.

 

Yes.

 

Moab style climbs won’t do it. Too little time spent on the incline. Face it the other direction on a longer decline, especially with driver side tilted down. Guarantee you’ll see it.

 

Like the Devils Staircase on Broken Arrow in Sedona? A descent that a Tacoma does probably once per day, at least?

Or does it need to be steeper than having your wheels locked yet still sliding down the ledges?

 

If you are referring to the low oil light that comes on at an incline then ya it can come on and it spends its time being ignored, only an issue if you dump oil back in through the PCV but that only occurs really on steep inclines. Let’s see your pics on window maker, that’s not something you just roll up.

 

I recommend Total Chaos, mainly because they are low profile, they go all the way to the top at the bed rail more maximum strength and you can usually just order on Amazon.

 

I’m really bad at getting action shots on my camera because I’m always driving.

 

But not widow maker

Honestly it’s getting like that for our crew. We only take pics when someone needs a spotter otherwise we just roll through.

 

Thank you sir

 

Ha same!