towing with my lowered crew cab

[stutaeng]

I'm not into lowered trucks much...even less notching/cutting a frame. I thought doing so was just for appearance, so I get that.

But from a strength of materials standpoint, any steel section that is deeper is going to be the strongest, for a given thickness. And the opposite is also true. Reducing the channel depth by notching, even if you box it, will most likely become a weaker section. I'm no mechanical engineer, but this is from simple beam mechanics theory.

I don't know the answer to the OPs question. I'm not sure how that could get quantified. At the minimum a photo is required. If someone can show me bridge girder that has been notched to half the depth and reinforced, at mid-span, I'd like to see that. It's all in the stresses imposed.

Just driving around on my 3500 CCLB SRW...the body seems to flex plenty over bumps, twisting ramps, etc. If anything, the frame is too flexible and lacks stiffness as it came! LOL. That's kinda true of older trucks in general though.

 

[618 Syndicate]

Towing something like a camper is much harder on the truck than a car trailer.

How so? Weight is weight, car trailer or pull behind camper the truck don't know the difference if the weight is the same. As far as gooseneck/5th wheel being different than a pull behind I agree, but again, weight is weight.

 

[618 Syndicate]

I'm not into lowered trucks much...even less notching/cutting a frame. I thought doing so was just for appearance, so I get that.

But from a strength of materials standpoint, any steel section that is deeper is going to be the strongest, for a given thickness. And the opposite is also true. Reducing the channel depth by notching, even if you box it, will most likely become a weaker section. I'm no mechanical engineer, but this is from simple beam mechanics theory.

Agreed, but you are replacing the removed material with 3/8 gusseted notches. I'm not an engineer either, but I believe that the gussets and thicker steel in the new section make it stronger than what it was before the notched part was removed.

I don't know the answer to the OPs question. I'm not sure how that could get quantified. At the minimum a photo is required. If someone can show me bridge girder that has been notched to half the depth and reinforced, at mid-span, I'd like to see that. It's all in the stresses imposed.

Just driving around on my 3500 CCLB SRW...the body seems to flex plenty over bumps, twisting ramps, etc. If anything, the frame is too flexible and lacks stiffness as it came! LOL. That's kinda true of older trucks in general though.

If the girder had been reinforced with stronger material it would probably be stronger even though notched. It is indeed about the stresses, reinforcement helps deal with them.
Bridges flex or they break. Ever stood on one as a vehicle crosses, or a strong gust of wind hits?

 

[Lanny]

I understand where Stutaeng is coming from with this one. As a civil engineer I've done a fair bit of material testing and worked through numerous materials problems. Both Stutaeng is right and 618 is as well. Pictures really are necessary because if the C notch section was made out of thicker material, theres a good chance its just as strong as the original section. C channel steel is not particularly stiff. Boxing it would help but the weakest section here is most likely the connection point between the frame and the notch. As you will probably be loading the weight directly over the top of the notch, I wouldn't worry too much about its stiffness.

Take a peek under and check out how thick the C notch steel is as well as the relative dimensions. That'll give us some information.

 

[letitsnow]

How so? Weight is weight, car trailer or pull behind camper the truck don't know the difference if the weight is the same. As far as gooseneck/5th wheel being different than a pull behind I agree, but again, weight is weight.

Weight is weight, that is correct. Wind resistance is the killer though.

You had stated that you pulled a truck "on" a car hauler. To me that means that it was on an open car trailer. If you put the truck "in" the trailer, than it would be comparable.

While some might say that wind has no effect on frame mods, maybe they are right? I really don't know, I just watch the way that the wind pulls my camper/truck around and I think of the forces on that frame...

I'm not saying that it won't work - just want the OP to be sure that he is getting accurate info.

 

[Supercharged111]

Weight is weight, that is correct. Wind resistance is the killer though.

You had stated that you pulled a truck "on" a car hauler. To me that means that it was on an open car trailer. If you put the truck "in" the trailer, than it would be comparable.

While some might say that wind has no effect on frame mods, maybe they are right? I really don't know, I just watch the way that the wind pulls my camper/truck around and I think of the forces on that frame...

I'm not saying that it won't work - just want the OP to be sure that he is getting accurate info.

His truck on a car hauler is no less than 8500#. There are tons of bumper pull campers that come in well under that. At some point it will offset the difference in drag.

 

[618 Syndicate]

Weight is weight, that is correct. Wind resistance is the killer though.

You had stated that you pulled a truck "on" a car hauler. To me that means that it was on an open car trailer. If you put the truck "in" the trailer, than it would be comparable.

While some might say that wind has no effect on frame mods, maybe they are right? I really don't know, I just watch the way that the wind pulls my camper/truck around and I think of the forces on that frame...

I'm not saying that it won't work - just want the OP to be sure that he is getting accurate info.

The aerodynamics of an enclosed trailer vs a open trailer are what I think you're talking about right? The side loading might have an effect on the frame with extreme cross winds, but a notch isn't gonna be a factor. The dual rear wheels will provide stability and the frame reinforcement I discussed earlier will provide more strength than was originally there.
I gave the op accurate information, but obviously we can discuss the "whataboutthis" scenarios until forever.

 

[BowtieJC]

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Thanks for all the replys. I will weld and box to strengthen the c notch and changing my rear bags to the airlift 5000. And pray for the best. Back in the 80’s and 90’s these lowered crew cabs were everywhere and all the hot rod shops had them and towed huge trailers with them. I wished i could buy a duramax dually but i love my OBS crew and its never leaving lol. I cant afford a late model duramax and a toy hauler . Sucks to be poor lol. This is my truck

 

[drewcrew]

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Thanks for all the replys. I will weld and box to strengthen the c notch and changing my rear bags to the airlift 5000. And pray for the best. Back in the 80’s and 90’s these lowered crew cabs were everywhere and all the hot rod shops had them and towed huge trailers with them. I wished i could buy a duramax dually but i love my OBS crew and its never leaving lol. I cant afford a late model duramax and a toy hauler . Sucks to be poor lol. This is my truck

Beautiful truck.

 

[stutaeng]

Agreed, but you are replacing the removed material with 3/8 gusseted notches. I'm not an engineer either, but I believe that the gussets and thicker steel in the new section make it stronger than what was removed.


If the girder had been reinforced with stronger material it would probably be stronger even though notched. It is indeed about the stresses, reinforcement helps deal with them.
Bridges flex or they break. Ever stood on one as a vehicle crosses, or a strong gust of wind hits?

Without running numbers I personally couldn't say "probably." Even if you make a smaller section SOLID, the geometry can be such that stresses can just blowup out of proportion (i.e., steel starts to yield and go into plastic deformation.) A metal paper clip getting bent with minimal force is good example...It's obviously an extreme example.

OP hasn't even stated if he did the design/work or any other details, or if he bought the truck like that...Did they use that cheap Harbor Freight flux core AC junk welder? Maaybe he's a certified welder. Who knows. Was the notch designed by a company that did finite element analysis of the capacity? Or was it Billy Bob hacking away with a torch and some oilfiled scrap metal? At this point we have more questions than facts.

I don't know what steel was used on these frames. The grades of steel used in the building industry that I work in are 50 ksi (A992) for wide flanges beams, tubes are usually 46 ksi (A500) but plates/channels and bars are only 36 ksi (A36.) The steel you get at home depot is all A36...So most likely the steel used to reinforce the frame is not "high strength." Then there's the weld filler metal grade: 70 ksi?...then there's the welding process SMAW, FCAW, GMAW, and GTAW...stuff starts looking gray. But if you say it's stronger, that's fine by me...

All I'm saying is that we are all just guessing here, LOL. Sorry guys. I'll stay out.

And vibrations on bridges are sort of another matter...Has to do with stiffness, mass, damping, natural frequency, etc...

Edit: Didn't see OP's last post. That is a very nice truck indeed! And any reinforcement is better than no reinforcement! Cheers!