So, I know over the years this topic has been beaten to death, but I recently dug in and did some research as to IF the current generation SD mild grade steel frame is actually superior to a RAM or GM frame which consists of primarily of HSLA Steel (High strength low alloy).


My findings aren't exactly heavily based in science, however, they are probably close to accurate.


If you take the Open C channel frame of the Super Duty, which is made from .26" 36,000PSI Yield strength Mild Steel and divide that correctly, you will see that the actually yield strength (given the thinner than 1" sq block that PSI is measured in) is closer to 9,360PSI Yield Strength.


However, if you take a RAM Boxed Frame, which is made from .15 (main sections from cab back) to .20 (front boxed section) 50,000PSI HSLA Steel and do the math, it actually has a yield strength of 7500PSI-10,000PSI up front.


Anyways, given the move to a Fully Boxed frame in the future Super Duty, I think its fair to say that the marketing gurus at Ford were clearly trying to jump on the band wagon in terms of overall strength. That's why the only marking you hear from Ford about the new frame is all related to rigidity and not actually frame strength.


Also, in order to retain ANY real strength from a thinner gauge yet fully boxed frame steel frame, you must use HSLA steel to compensate for the lack of material. This is why you see all the manufactures going to High Strength steel in their frames when boxing them.




Here are some pictures I took from both my trucks frame and a 2016 RAM 3500 frame. From 6" and then from 2" away.


Enjoy

 

This is the video that is often connected to this issue.

 

Here's the video I made to rebuke that video

 

So who's winning ? I think but i may be a little biased.

 

Totally agree with Iron Cobra, it's going to be one of my biggest concerns when I order the 17 F-450 the c channel has always been a durable and work friendly frame his videos correct flexing and giving is much better than being rigid. Totally concerned with plow with the truck too knowing how for decades Super Duties handled the plow and the impact of snow piles what will its new rigid frame think of the impacts year in and year out? Chevys are well-known to bend in between the cab and bed where the super duty would never fail time will tell

 

All I ever watch are the Class 8 heavy duty trucks.........they all use "C" channel frames.......no marketing hype and other BS involved!!
Now the EXTRA heavy duty will go to double channel.....but, if "C" channel is good enough for them, it is good enough for me!!!
Thanks for sharing!

 

Im not quite sure where you are getting this math from. 36 Ksi steel is 36 Ksi steel, no matter how thick it is. The rigidity of steel is pretty much constant, no matter what the grade. In other words, two truck frames constructed the same way, one with 100 Ksi steel and one with 36 Ksi steel will flex exactly the same amount under the same load, until the 36 Ksi one breaks. You will be able to continue to flex the 100 Ksi frame further - under a greater load - before it breaks.

The big marketing point here is torsional strength. A "C" section has much less torsional strength compared to a box section, no matter what material is used. The bending strength is pretty comparable to a box section, using the same amount of steel (actually the box section will be only about 75% as strong and as rigid in bending, but much stiffer in torsion). The use of high strength steel in either case will either increase the amount the frame can be flexed before it breaks, or allow the use of less steel for the same breaking strength. This is why in the video they did not show bending the two frames, it would not be much different (or the box frame weaker). They show twisting the frames.

In a race car, torsional rigidity in the frame is essential to suspension tuning. In a truck, it isn't all that spectacular an advantage, probably improves ride a little, and might keep your tailgate from jamming if you are foolish enough to high center it diagonally. You might also be able to cut down on the number of cross members (which aid torsional rigidity in a C section frame).

 

My logic is that if 36k psi steel is based on a square inch, it is not taking into account the gauge of the steel if it's less than 1" sq. So technically if the thickness of the steel adds torsional rigidity vs steel that is thinner. If you eliminate thickness you also decrease that steels ability to maintain its original PSI rating when force is applied.

 

I am not totally sold as on the box frame concept. As 99150 stated the larger trucks use C channel frames. I know that with the last set of custom fire engines we bought the manufacturer uses a double c-channel frame. Since they custom build every frame they could use anything they wanted, but they choose the double C.


As with the nature of large scale manufacturing, I have to imagine that cost plays a role somewhere. For the strength desired, the box may be cheaper to use. The box may end up to prove to be a superior design, but my C has held up to 293K of hard miles and is still doing just fine.

 

You are not using the terms as an engineer would, though your conclusions are basically correct. 36 Ksi spec steel is 36 Ksi spec steel, no matter what it is formed into. A particular piece of 36 Ksi steel measuring 1" x 1" will have a strength of 36,000 lbs in tension, while another piece of the same steel made 1/4" x 1" will have a strength of 8000 lbs. Both pieces still withstand 36,000 lbs per square inch.

The bending strength of a steel section depends on the distribution of the steel across the section. A section with 1/2 square inch of steel properly distributed can be stronger and stiffer than one with 1 square inch poorly distributed.

A "C" section (Or "I" section, which is just two back to back Cs) is not a bad shape for bending, but is a poor one for torsion. If a "C" is boxed in with the same thickness of steel, it will be stronger in both bending and torsion - but it will also be heavier, so usually thinner material is used.

In the example you gave above of 0.26 C vs 0.16 box gage steel, I don't know the other dimensions but let's take 9" tall by 3" wide as an example. They will weigh nearly the same, but the C will be 20% stronger and stiffer in bending, if made from the same spec material. The box was made of 50 Ksi though, so it will be 16% stronger, in spite of it's weaker section. The stronger steel does nothing for stiffness, so the C will still be 20% stiffer.

In torsion, the box will be about 6 times as stiff as the C. But about the only time a truck frame is heavily loaded in torsion is in a test like the video. That isn't what I do with my truck. If you bought it for rock crawling, then the box section would be much preferred.

 

I like C channel frames.
You can hose the muck out of them easily.

 

I wonder how the box frame is going to handle the salt in the rust states.

 

I guess that depends on how well E-coating holds up to salt. I know most manufactures moved away from waxing their frames a decade ago or so.Super duty started e-coating around 2006 I believe, not 100% sure though.

 

Wow......where were all the c-channel pundits when Ford was saying how much better the box frame was on the 150???

I always giggled at that ignorant silver creek test and questioned why Ford didnt run an F-250> on that course.

Now that GM threw that nonsense right back at Ford.....well, we all see what's happening...lol!!@

Signed:

A very satisfied F-350 owner with no (gasp) frame issues to date.

 

Ummmmm......the same as the '04 and newer 150's???