The Strength of Different Styles of Frame Notches (Info)

[cpolaris502]

I found this posted on GMFullsize.com which was linked to 67-72chevytrucks.com. It talks about the different styles of notches, both step and bolt in and how stong each is compared to original. Some of the data was pretty insightful and a little scary to me!

http://67-72chevytrucks.com/vboard/s...d.php?t=457037

[DROPTSBLAZE]

I wonder how strong a taller tube type notch would be. I wonder if height of the notch would affect it?

[lowdime96]

thanks for the info!

[tsayyote]

Thanks Cory, I have always wondered how notching affected the strength of the frame. It's nice to see some numbers from an engineering standpoint.

[90blueS10]

Makes me feel a little better. lol

[lowsdime99]

Wow that is a little Scary def have to go with the half circle if I ever start another truck!

[cpolaris502]

Here is the original post from 67-72trucks.com. All credit goes to lakeroadster for the original post and information. I am simply copying here incase the link goes bad in the original post.

Maybe a mod can edit the original post in this thread to contain this info?

Quote:

To discuss this topic go here- LINK


I reviewed this thread and was concerned that some of the information that was posted would be taken out of context and misused. To prevent this from happening I deleted my posts and reworked the data into the following:

Frame Notch Based On Strength


Frame Notch Based On Strength
A lot of guys are notching their frames to lower the trucks stance. As a Mechanical Engineer some of the photos these guys have posted on various websites reflect notches that are scary.

Please note that I don’t have a dog in this hunt; I am not selling anything. Don’t shoot the messenger, I am merely trying to help.

How you notch your truck frame should depend on its original factory design and how it will ultimately be used by you or any future owner. My personal philosophy has always been any change to the frame should restore the original strength, but that is me. I always assume that just because I may never push the envelope of my truck to its rated capacity doesn’t mean the next owner won’t.

Things to consider:

How do you plan to use the truck? If those plans include hauling loads in the truck or pulling a trailer with the truck the frame will see these loads and frame strength will be very important.

Long bed trucks load the rear frame section more than short bed trucks.
A look at various designs using Finite Element Analysis
A Stock Frame (based on a 65 C10) is the baseline for all of these designs. The FEA assumes a factory stock standard coil spring / trailing arm type suspension, circa '65 (I have been told that the suspensions from 63-72 were all very similar) and assumes a bending moment from hauling and towing loads. Worth noting is that if hauling and towing loads are not present the trailing arm suspension style frame has almost no load at the rear axle, only the weight of the frame itself and the truck bed.

A Stock Frame (based on a 65 C10) is the baseline for all of these designs. (See 1st attached picture)





Commercially Available Notches

Bolt In
This model replicates the popular bolt in notch, it gains you about 3-1/2" additional clearance. It captures the bottom and the outside of the frame and is ¼” thick. The frame is not boxed. FEA reveals the frame is 80% weaker than stock.

Bolt In Type Notch (See 2nd attached picture)




Add a welded in boxing plate to the back of this design and the FEA reveals the frame is still 60% weaker than stock. (See 3rd attached picture)




Weld In (Dim. data was taken from this website: http://www.suicidedoors.com/notches/...step-notchkit)

The half circle notch is slightly stronger than stock (about 10%) and gives about 8" more travel. (See 4th attached ppicture)

Half Circle Notch FEA




The Step Notch is slightly weaker than stock (about 10%) and gives about 8" more travel. (See 5th attached picture)
Step Notch FEA




DIY Weld In Notches

Pipe Notch. This yields 2" more travel than stock and is as strong as a stock frame. It utilizes a 3/8" reinforcing pad and a 1/4” boxing plate to accomplish this. (See 1st attached picture in next post)

Pipe Notch FEA




Deep Pipe Notch. I saw this being done on one of the websites. It was a boxed installation and it is about 76% weaker than stock! (See 2nd attached picture in next post)

Deep Pipe Notch FEA

(See 3rd attached picture in next post)




Step Notch made from rectangular tube. Here is one I developed that is made from mitered 3-1/2” x 2-1/2” x ¼” wall tubing. It is about 10% stronger than a stock frame and gains you about 3-1/2" additional clearance. (See 4th attached picture in next post)

Tube Type Step Notch FEA



Tube Type Step Notch as viewed from inside. (See 5th attached picture in next post)




Summary

If you want the frame to be as strong as stock and you want a frame notch deeper than the 2" there is simply no substitute for adding some sort of truss structure, or replacing the frame section with another structural member that has the same or greater section height as the original frame.

Whenever someone starts talking about a deep frame notch (> 2” nom.) and state that just by adding thicker plates to the sides of the frame rails this makes the frame stronger than it was in its original condition, yet they are and not adding vertical height, they do not understand beam analysis.

Some final thoughts

The implementation of any design affects its strength. The final fabrication can only be as good as the welder – fabricator performing the work.

I have yet to see a bolt in notch that will restore the strength of the frame to the factory condition.

I have not seen any manufacturers “certifying”, via a signed document, the strength of their notch kits.

The information posted here is for reference only. Results will vary based on actual dimensions, materials used and the quality of the implementation and fabrication.

Backup photos:

[cpolaris502]

More pictures.

[SoloSDN]

if someone is notching a truck,they should already know this Good info though

[squareterror]

not everyone is an engineer. i would have never thought that a bolt in notch would make its that weak, nor a step notch be weaker as well. pipe i do understand entirely though. doesnt even look like it'd be very strong

[lowdime96]

Interested to see how strong a bolt on step notch that ART or lowrider depot is.

[jwillie000]

is the stock frame overkilled then ?

[colbye32]

I can see how bolt in notches make the frame weaker than stock, but seriously how many people have had trouble with them ? I think bolt in c notches, and step notches are fine, ive had both with no issues.

Does anyone have any info on say bolt on backhalfs? I've had one of those also, just curious to see if its stronger or weaker than stock, since youre cutting off the stock backhalf, and relying on bolts to hold it to the existing frame. I know some people weld them, but still.

[squareterror]

i would imagine it would be weaker, because you no longer have a continuous piece of steel. you would have two "rubbing" against each other. but i'm no structural engineer.

[chapdou]

Quote: Originally Posted by squareterror

i would imagine it would be weaker, because you no longer have a continuous piece of steel. you would have two "rubbing" against each other. but i'm no structural engineer.

In this case the problem will be not the rubbing. It that a the will be on the area around the bolt. Because the bolt will not be a problem ( 1/2 bolt grade 5 it around 10 000lbs in shear) but the small area around bolt have to hold all the stress. So if the hole are near a eedge or another hole it could be really bad.

[JeremyCollins13]

please repost that in english, just in case there was something of use in it.

[tsayyote]

Go easy on him, man. English isnt his primary language.

But what he's saying is that the metal just under the head of the bolt is taking a lot of stress. I've actually seen a bolt get "pulled through" a piece of steel with the bolt still 100% in tact and a gaping hole left in the steel.

[JeremyCollins13]

ok... See, I didn't get that at all. Thanks for clearing it up.