F100 vs. F250 frame steel thickness

[FORDification]

I finally got around today to measuring and comparing the frame thicknesses of an F100 and F250 frame, to verify what I've been told....that the F250 frames were made of heavier steel. Just with a visual comparison it did seem the F250 frame was thicker, but I wanted more accuracy. I used a standard micrometer and measured in three different spots on each frame: front, center and rear. I got the same measurements in each spot on each respective frame, so we know that the thickness remained constant from front to back. The frames I measured included a '68 F100 and a '67 F250. Both were cleaned well with a wire brush at all measuring points to ensure accurate and consistent readings.

...and the final verdict?

The F100 frame measured .171" thick and the F250 frame measured .200" thick....a .030 difference between the two. I did a search online for a chart to convert these measurements to 'gauge' readings, and the conversion charts I found showed that the F100 frame would be app. 7-gauge steel whereas the F250 would be app. 5-gauge steel. I checked these with several different online conversion charts and found them to be fairly consistent, though one site mentions "Actual thickness will vary depending on the mill it was rolled at, batch number, etc."

So now you know. I've added this little tidbit of info to the 'Did You Know' box at the top of each page.

[68F250]

Very good, thanks for checking that out!

So, putting the pieces of the puzzle together, the “Fact & Featuresâ€Â

[FORDification]

Sombody else will have to help out with the 4x4 frame measurements, as I have no access to any '67-'72 4WDs around here.

...and I'm not ashamed to admit that you've completely lost me on what "Frame Sectional Modulus" is. I've never even heard of that before. Can you put that into laymen's terms?

[ttyR2]

I took it to mean torsional rigidity, how easily the frame can twist.

[discman]

My 1970 F100 Was bent in the center, as you could tell by looking at it sideways. I had a frame shop rebend it to somewhat straight. The only problem is that as soon as you load it up again, or overload it I guess. It will, again, sag in the middle. All the F250s I see are straight as an arrow. I've been thinking of reenforcing it somehow.

[68F250]

Keith, I had to blow the dust off the books and am almost on the verge of comprehension so here goes, help me out guys!

Frame Section Modulus: engineering term that indicates the relative strength of a frame as it relates to its shape. It takes into account the frame depth, flange width and material thickness. It is a property of the cross sectional shape and its amount of stiffness.

Section modulus (S) is also equal to the moment of inertia (I) divided by the distance from the centroid to the edge of the section (c) so S = I/c. Moment of inertia is a measure of the “efficiencyâ€Â

[Comet]

That's very interesting Keith. I have never been able to confirm that, but heard it before too.

[NM5K]

Frame Sectional Modulus......

Hummmm...I'd wondered what that meant...
I'd seen it in the original ford brochures in the
chassis specs....MK

[ttyR2]

discman, if the bent frame was caused by a one-time severe overload, it may not bend again in normal usage.

[rjewkes]

But could you bolt to a 250s frame your entire body and there for have a stronger frame under you? although i must say that the .177 or 7 guage is pretty good and solid in its own right.

[FORDification]

Sure...you can bolt the entire F100 body and suspension to an F250 frame and have the best of both worlds....that is, a 5-lug setup on a frame that's sturdy enough to do some regular heavy towing.

If anyone in the area wants an F250 frame, I've got one that's going to be otherwise sold for scrap within the next week or two, unless someone wants to haul it away for me.

[rjewkes]

Dang and i'm so far away.

[Comet]

Keith, no one has come forward with an answer for the hi boys on this question. If you tell me exactly where you measured your frame thickness at, I'c be willing to go check my '71.

[FORDification]

Cool...thanks! Just use a standard micrometer to measure the frame thickness in several spots down the frame...it really doesn't matter. From my experience the readings should all be the same. Just make sure to really clean the metal well with a wire brush first, to eliminate erroneous readings from rust.

[Comet]

Ok, we'll do. I have tomorrow off and unless it's really raining hard I'll do it tomorrow.