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Do Doors Add Strength, Thread

OT

NAXJA Forum User
Location
Jensen, UT
There is a debate on several threads going on, about the structural strength provided by doors and hatches.

I am of the opinion that any FACTORY hinged panel is not intended to add strength to the unibody.

I mean think about it. If a body wanted to twist up enough for the rear hatch to be the limiting factor, don't you think it wouldn't hesitate to rip the catch right out of the fiberglass structure of the hatch? (I know late models have steel hatches)

As for the door issue, if the same twisting really was limited by the doors, then wouldn't worn hinges negate that theory?

I certainly wouldn't feel comforted knowing the integrety of my XJ's stucture relied on a few skinny doors and a few little catch pins.

But I must say, the most insane theory would be the "if you pull off your doors you'll get death wobble" theory. :bs: The silliness of this is rather self explainatory.

Edit: This relates to the topic of MODIFYING hinges for quick removal of doors and hatches.
 
Last edited:
JnJ said:
U must be from Okiehoma.....

Oh ya, I think this is OEM Tech.

Oh ya, this thread already sucks.
Actually I think it's Non-tech or even borderline Off-topic, but I wanted it HERE, so nnyaaahh.

yeehaw
 
dennisuello said:
and this has been discussed how many times? is it worth starting another thread on this?
Sure it is.

I'll pay for the bandwidth. Oh wait, I already have.
 
Ok. If you remove the doors it will cause death wobble, fuel delivery problems, and it is not approved by any race sanctioning body. Oh and it will fold like a taco.
 
all one needs to do is study the design of the latch assy to see that all it does is keep doors closed.

it doesn't reinforce the unibody.......

a little common fawking sense goes a long way....

if you remove a doorframe in a house, does the wall collapse?

why would enginners design a fawkin door to be a major componant in the strength of any form?
 
JnJ said:
Ok. If you remove the doors it will cause death wobble, fuel delivery problems, and it is not approved by any race sanctioning body. Oh and it will fold like a taco.

But I'm OK without a front swaybar, right?
 
If you are building in removable doors you should have a roll cage tied into the subframe. This makes the structural point moot.

Nay
 
Beezil said:
all one needs to do is study the design of the latch assy to see that all it does is keep doors closed.

it doesn't reinforce the unibody.......

a little common fawking sense goes a long way....

if you remove a doorframe in a house, does the wall collapse?

why would enginners design a fawkin door to be a major componant in the strength of any form?

You don't drive your house.

Or do you?
 
With the doors in, the A pillar (and windshield) will collapse, to a rather striking degree, between the doors (the top front corner of the door pops out a bit), the front door corners are largely the only thing keeping the roof from going totally flat (along with the B pillar).
If I was going racing I´d figure out an L bracket welded to the A Pillar, to catch the top of the door in a roll over and add a roll cage, keeping the A pillar in mind. More is better.
To say this in another way, the roof/windshield /A pillar, collapses between the doors in a pretty mild rollover, roof ends up just above the front seat headrests. Or pretty much a straight line from the hood to the top of the B pillar. If your over say 5'8" leave the doors in or install a serious A pillar B pillar roll bar.
But what the heck do I know, I just drive the tow truck.
By the way, have seen guys run wthout doors, put the doors back on and couldn´t get them to shut again. My guess is they add some kind of rigidity to the frame.
 
i think there is some validity to the roll-over point, but as far as chassis flex, the doors do nothing. the reason you've seen guys not be able to get their doors back on is that the stupid hinges are a freakin pain in the *** to line up right.

in the summer i leave my doors off whenever i'm driving around town or on a mild trail (no AC), but if i'm hitting a harder trail, the doors go on so that i can drag a door on a rock rather than myself. getting an exo-cage with a removable door bar would remedy that problem.
 
8Mud said:
By the way, have seen guys run wthout doors, put the doors back on and couldn´t get them to shut again. My guess is they add some kind of rigidity to the frame.

This simply means that they don't know how to align them properly when they put them back on. There is substantial room for adjustment built into the hinges.

I don't believe the doors have any strength vertically or torsionally speaking, but obviously horizontally they provide a great barrier for rocks, trees, Hondas, etc... Most of us are high enough now where a honda would go straight under our doors and into our rock rails or maybe clear underneath in a side impact, but there have been plenty of times where a rock has come up real close to my door and if i was another 6" over, it would be in my personal space. I don't like rocks in my personal space..... :D
 
Counterpoint:

Park a stock XJ sort of twisted up.

Open the rear hatch to pull out some gear like lawn chairs, lunch, etc.

Now close the hatch.

You can't!

The unit body has twisted and the latch assembly no longer goes in the correct place.

To be clear/precise:

I'm NOT saying the the doors and hatch assembly were DESIGNED to be structural components.

I AM saying that the XJ platform/unibody IS FLEXIBLE like a wet noodle and should be dealt with if you are really planning on leaving pavement.

As always, just my spin.

r@m
 
Beezil said:
all one needs to do is study the design of the latch assy to see that all it does is keep doors closed.

it doesn't reinforce the unibody.......

a little common fawking sense goes a long way....

if you remove a doorframe in a house, does the wall collapse?

why would enginners design a fawkin door to be a major componant in the strength of any form?

:worship:
 
ECKSJAY said:
But I'm OK without a front swaybar, right?

Yeah, I have mine off on my 91' xj with 35" mtrs & 7-1/2" of lift and short arms. There is more body roll when turning, but I've adjusted my driving style and take it slower. You will need the track bar though because this is responsible for the lateral stability and location. I took my front sway bar & track bar off of my 10" lifted 94' wrangler with a spring over with leaf springs. The leafs are great in that they locate the axle and are also the susp unlike the coil spring that can flex better but needed multiple links to locate it and the coils to provide the susp.
 
Safari Ary said:
I don't like rocks in my personal space..... :D

I hate 'close talker' rocks too.

I pulled the doors too 'cause I like tacos.
 
2¢ more...

Picture the main structure of the XJ as a simple box as in drawing A below. With all six sides of this box enclosed, an input to one of the corners would impart a twisting force on the box. In order for the box to twist, some of the panels have to distort as pictured in drawing B. The roof, floor pan and firewall/windshield act as sheer panels on three of the six sides of the box, effectively eliminating this type of distortion on these sides.

The left and right sides and the rear are for the most part, open, and therefore rely on corner strength to resist the distortion pictured in drawing B. Metal in the corners is sometimes double thickness and the corners are radiused to bolster the strength, but without the benefit of a sheer panel, the three open sides are not even a tenth as strong in resisting torsional loads applied to the chassis. Force is applied at the corners with the length of the sides acting as a lever arm having a 10 to 20:1 advantage over the corner strength.

Now place doors in the openings of the side and rear panels. The doors, in contact with the weather seal moulding, are a loose fit in the openings. They act as a floating sheer panel, providing little resistance to small distortions in the structure, but resist larger distortions. More importantly, a fairly rigid triangle, pictured in drawing C is formed between the two hinges and the latch mechanism. This triangle adds considerable strength to the door opening, effectively cutting down the opening size by half. Bending moments at the front of the door opening are transferred into near vertical movement at the latch. The latch mechanism and the door pillar it attaches to are designed to handle loads in the vertical plane. At the rear, a similar triangle is described by the upper hinges and bottom latch of the lift hatch. Distortions pictured in drawing B result in horizontal movement at the latch.

You can see where adding a tubular X member to each of the openings as shown in drawing D would add strength similar to that of the sheer panels. With the chassis under torsional load, one tube would resist in tension and the opposite tube in compression. It isn't practical to do this, but even one X member across the B or C pillar area will overcome much of the weakness of the rear hatch opening. Adding diagonal membrs along the sides will help reduce the loads at the corners of each door opening.

Add X or diagonal members to the extent possible as a substitute for the lack of sheer panels on the three weak sides of the chassis "box".

Consider this analysis vs the practice of plating the frame rails. Adding material to the uni-rails will harden the rails against impact and can spread the load of suspension attachment points over a broader area, but will add little to the torsional strength of the main structure as the floor pan is already one of the strongest sides of "the box".

torsion_box.jpg
 
proof of what can happen. RevDen left his doors on, but removed part of the roof. Result: TACO TIME

RevDen_Taco.jpg
 
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