Frame Stiffness ?

Inc · **Posted:** Mon May 04, 2009 1:21 am

A while back on here I saw some percentage figures about how much stiffer the KJ's Unibody is than the XJ's.

Anyone know those figures? If you do, what are they, and where did you get the info so I can check it out.

Thanks.

Guest · **Posted:** Mon May 04, 2009 2:45 am

SOTP twist-o-meter says 9,341,658% stiffer in torsional rigidity, and 4,925,944% better in bending rigidity.

Doesn't really matter, because the KJ is built like a brick outhouse, and the XJ is built like a doo doo brickhouse :lol:

Just go tell an XJ guy to open his door when flexed out so he's cross-axled, and then see if it closes. CJs can, FSJs can, ZJs/WJs can, KKs, WKs, ZKs, MKs can, KJs can :lol:

Numbers are not important in this comparison.

That being said, ThunderbirdJunkie will dive into his old MT's and C/D's to try and find a KJ article from "back in the day"

Fulltimer · **Posted:** Mon May 04, 2009 5:14 am

I had read somewhere a statement by Chrysler where they said the KJ is the strongest body they had ever produced. No idea where I read that. Sorry it doesn't really help you any though.

Terry

JJsTJ · **Posted:** Mon May 04, 2009 8:14 am

Yeah I still need to add a couple crossmembers back in but my d/s door is tweaked from flexing it out. Never had that problem in my XJ.

But I do believe it is a stronger structure overall. Really only a few that are maxing it out though to test the theory that it truly is stronger and will last longer under big flex conditions.
Hey if all else fails though we can just start plating the frame like the XJ's and ZJ's do.

tomsjeep · **Posted:** Mon May 04, 2009 8:46 am

I recall reading (but don't recall where) that the KJ has the strongest roof structure of any Jeep ever built. That may have been here...
http://www.allpar.com/model/jeep/liberty.html

Quote:

Liberty has the highest roof strength of any Jeep vehicle.

jsc7002 · **Posted:** Mon May 04, 2009 11:24 am

JJsKJ wrote:

Hey if all else fails though we can just start plating the frame like the XJ's and ZJ's do.

just add a frame, this guy turned his XJ unibody into a frame, looks good but a lot of work.

http://www.jeepforum.com/forum/showthread.php?t=741237

Inc · **Posted:** Mon May 04, 2009 1:01 pm

JJsKJ wrote:

Yeah I still need to add a couple crossmembers back in but my d/s door is tweaked from flexing it out. Never had that problem in my XJ.

But I do believe it is a stronger structure overall. Really only a few that are maxing it out though to test the theory that it truly is stronger and will last longer under big flex conditions.
Hey if all else fails though we can just start plating the frame like the XJ's and ZJ's do.

I was looking at Ruff Stuff's XJ frame stiffeners and they look like they would work with some very minor modification. I talked to Dan and he said he could easily make me some if I got him exact measurements, but I didn't ask a price for a custom set so it may be cheaper just to mod the XJ ones. I am also looking to integrate a rock rail into the side of the unibody which will also add stiffness. Instead of bolting the rock rails to the frame or welding them on, I would cut out some of the unibody side paneling and weld in a 2x4 or 2x6 metal rail that will be stiffer than the part I cut out and will be perfectly functional rock rails. Plus I'll gain like 4 or 5 inches of side clearance since I won't have the rails hanging low anymore.

I wish I could find the thread where the percentages were discussed.

Fulltimer · **Posted:** Mon May 04, 2009 1:58 pm

Here is some interesting info. They mention the roof strength also: http://www.allpar.com/model/jeep/liberty.html

Terry

Fulltimer · **Posted:** Mon May 04, 2009 2:08 pm

This might be more of what you are looking for:

The part in question is a reinforced swinggate inner. Sixty-five welds are produced in 32 seconds. This work is being performed in the DCX Sterling Heights, Michigan, stamping facility. Jansen says that they had developed approaches for both spot welding and laser welding the component; thanks to a reduction in equipment (e.g., transfer devices) that the laser setup permitted, the total investment proved the case for the laser rather than traditional spot welding. To put some of this into context: compared to the Liberty's big, older brother, the Grand Cherokee, its bending stiffness is 58% better and its torsional rigidity is 43% better.

Here is the link: http://findarticles.com/p/articles/mi_m ... _76445143/

Terry

Inc · **Posted:** Mon May 04, 2009 2:29 pm

Thank you Terry, good info.

Jeepjeepster · **Posted:** Mon May 04, 2009 3:29 pm

ThunderbirdJunkie wrote:

SOTP twist-o-meter says 9,341,658% stiffer in torsional rigidity, and 4,925,944% better in bending rigidity.

The kj is pretty dang stiff and its balanced well also. I had jack stands under the frame just in front of the rear axle and in the little notch in the frame just behind the front suspension. Our garage floor isnt exactly level so the Jeep was really only sitting on the RR and FL jack stands. I could move the front right of the Jeep up and down with one finger and all the door opened just fine.

Frame Stiffness ?

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