towing with my lowered crew cab

[df2x4]

I remember many years ago watching a TV show in which the crew was lowering a truck. Can't remember the name of the show, I was a little guy. But I remember them saying that if anything the truck would be more stable while towing due to the lower center of gravity. Blew my little kid mind at the time but it made sense.

 

[drewcrew]

Its all about loading and how how that load transfers through a structure.
Imagine if you had a 14 foot piece of 4x4 square steel tube.
We could support it on both ends while ten of us stood on it and it might deflect a 1/4 inch maybe.
Because we are applying a concentrated load but the structure transfers that load to the ends of the tube.
The top of that tube we are standing on tries to squeeze itself together.
The bottom of that tube is trying to pull apart.
The sidewall of that tube transfers that load away from the failure point and keeps that tube from failing because of its form

Think about a 1/4 thick piece of 4 inch flatbar that is 14 feet long.
If we lay it flat on some blocks.
I can sit my ass on it and bend it.
I can step on it and bend it.
Take that same flatbar and restrain it in a verticle position so it cant deflect and your whole family can stand on it and wont deflect.
A C notch changes the load from being mostly a linear load to a load that transfers through a hard welded corner or change of angle.
And then all of that linear characteristic and strengh and ability to tranfer a load is done.
Metal structes do not carry their properties through welds.
And the weld is the weak point.
And the heat affected zone adjacent to the weld.
Box the frame way past the C notch and weld it up.
Its all about getting the loads transfered away from your notch.
Not about keeping them on and loading the notch.
You want that "energy" and "work" to have a place to transfer down the frame so it doesnt point load at the notch or the welds.
Plate it over the c notch and past it fore and aft and weld it.
Weld the frame box to the notch.
Then figure out how to weld that new frame to the truck.

I'm not saying your wrong but I don't agree the weld is the weakest point. I was in the pipefitters union as a welder for years. We were taught if you use the right rod (stick welding) that has a higher tensile strength rating than the base metal the weld is the strongest point.

 

[Supercharged111]

I remember many years ago watching a TV show in which the crew was lowering a truck. Can't remember the name of the show, I was a little guy. But I remember them saying that if anything the truck would be more stable while towing due to the lower center of gravity. Blew my little kid mind at the time but it made sense.

Pure speculation (and at best, hair splitting), especially depending on how the front was lowered. I'd forget you ever heard that.

 

[df2x4]

Pure speculation (and at best, hair splitting), especially depending on how the front was lowered. I'd forget you ever heard that.

Oh I wasn't taking it as gospel, I don't even remember what model truck they were talking about. I just thought it was interesting to hear someone with more knowledge than myself state that lowering a truck wouldn't necessarily negatively impact it's ability to do truck things. Just adding to the conversation.

 

[Supercharged111]

Oh I wasn't taking it as gospel, I don't even remember what model truck they were talking about. I just thought it was interesting to hear someone with more knowledge than myself state that lowering a truck wouldn't necessarily negatively impact it's ability to do truck things. Just adding to the conversation.

Ahh OK, that's a better perspective than what I drew from it.

 

[thinger2]

I'm not saying your wrong but I don't agree the weld is the weakest point. I was in the pipefitters union as a welder for years. We were taught if you use the right rod (stick welding) that has a higher tensile strength rating than the base metal the weld is the strongest point.

That is true but only happens if you know how to weld.
And that is rarely the case in DIY welding.
To properly stick weld something as thin as a frame is a pretty rare talent.
What usually happens is they grab a rod out of a can thats been open and in the unheated garage for 5 years and soggy as hell. Aint no amateurs using a rod oven.
And they dont notice the flux popping off of the rod and landing in the weld puddle in chunks.
And they dont prep the joint or preheat it or multi pass/ backgouge etc..
But they will blow half a can into a 4 inch weld.
So you are right, it may not be the weld itself that fails.
But the undercut base metal that got heated into taffy right next to that weld is weak as hell.
So the weld doesnt necessarily fail, the heat affected zone adjacent to it fails.
MIG has its own set of problems including bad prep lack of penetration not understanding the difference between spray transfer and globular etc..
Wrong gas, no gas, welding in the wind while the shielding blows away and on and on..
All of this leads to porosity and inclusions and surface welds with no penetration and welds that look like a porcupine from all the wire sticking out.
Im sure youve seen it.
Boxing the frame not only transfers the loads, it also adds redundancy to the structure because it has more welds spread over a greater distance.
This is especially important if those welds are sketchy to begin with.
And dont even get me started on people who weld frames with a harbor freight flux welder and think they are MIG welding

 

[Mr Eric]

I'm not saying your wrong but I don't agree the weld is the weakest point. I was in the pipefitters union as a welder for years. We were taught if you use the right rod (stick welding) that has a higher tensile strength rating than the base metal the weld is the strongest.

Situation like this lead to problems.

We don't want a weld or an area welded "stronger" we want it to be as strong as the original. If it's less, then that's a problem, more reinforced isn't always a great thing either, as now the flexing that used to occur doesn't or it moves to a different location. Bending moment and location are not well thought out, some of the kits I have seen are a sledgehammer approach. Just adding a bunch of thick metal for stiffness is not something that fixes everything. Does it work? Perhaps, it might be a bandaid. Well on cause a failure, no, not likely. The safety factor, the idea that a c framed truck is going to flex a lot going down the highway isn't a big reality either so making a section of the frame rigid from the reinforcement added may never be an issue.

Bottom line, is isn't factory. If whomever does this understands all this, and says " I'm OK with it" well welcome to 'Merica, land of freedom to do things.
Understand however that the responsibilities are not in the factory anymore, they are on the builder. That's a liability and most people have never really thought that whole angle through.

Do what you want, but live with the consequences...... build and man up.

 

[TC Cunha]

were looking at getting a KZ Sportster 331TH13 toy hauler 5th wheel. my C3500 has been lowered 5/7 with C notch. the camper will weigh fully loaded about 11500 pounds. will the c notch be ok or is that too much weight . thanks

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I bumper tow my race trailer with the car and all the track day stuff... 8K total.. My baby is a 7.4 gas motor.. torquey and tows like it isn't even back there.. though the gas gauge says differently!

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[93chevyluvr]

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If it's installed properly (I suggest welding and bolting it) the notch won't be the weak spot.
I strongly recommend helper bags with an on board compressor as well.

Found these on a website

 

[Chris Westphalen]

Just for a little more info: with the way the stresses are generally applied to the truck's frame with a bumper pull trailer, the strength of the frame is proportional to the cross section. So, if you are cutting out 1/2 the height of the frame and doubling the thickness with the brace, you are breaking even. If you remove more than 1/2 the height, you will need to increase the thickness by a proportionate amount.
Also, if you are not a competent welder or do not have the right equipment, you are better off just bolting the brace to the frame. The shear force a 1/2" grade 5 bolt can withstand is 10,000 lbs. A grade 8 is 30% higher. So having 6 to 8 bolts through the frame and brace will more than handle the stresses applied. As mentioned above, the Heat Affected Zone around the weld is the weakest area. An improper weld can reduce the strength by far more than removing material did, just due to changing the properties of the metal.
Therefore, I believe most c-notch kits on the market are designed well enough to support the max tow ratings of the truck.