From the Experts: Why the 2018 Jeep JL Wrangler MAY come with a Fixed Roof

wayoflife

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I know there are a lot of purists out there who what to chastise Jeep for making all the changes that we'll most likely see on the new JL Wrangler that is expected to be released in 2017 but really, you need to understand that their hands are tied and are being forced to make these changes thanks to the government. You ever wonder why cars no longer come with pop-up head lights or why nobody ever makes T-tops anymore? Well, you can thank the NHTSA (the National Highway Traffic Safety Administration) for that and while there is a “convertible exception” in the FMVSS 216 rule that essentially allows open-top cars to "resist less force than other vehicles", this may all change and very soon. Needless to say, the possibility of the new JL Wrangler coming with some kind of fixed top may be something that Jeep will be forced to make. You can read what the experts have to say in the following AllPar article below:


2018 Jeep Wrangler in depth: Convertible/roadster or fixed roof?
by Robert W. Sheaves (edited). Part 6 of a series. Written in mid-October 2014.

2017-wrangler-hardtop.jpg

Bob Sheaves was responsible for 4x4 suspension design at the Jeep/Truck Engineering's PreProgram Engineering Department from the AMC days until 1993.

Allpar’s members asked what we are likely to see as the next-generation Jeep Wrangler. This article is based on my engineering evaluation of various public sources, plus private discussions.

2018 Jeep Wrangler: “convertible” or fixed-roof?

A regulatory change in 2009 is why there are now no more T-tops.

The reason why Wrangler may not be able to remain in its current form is because NHTSA (the National Highway Traffic Safety Administration) may change its rules. Currently, there is a “convertible exception” in FMVSS 216 which allows open-top cars to resist less force than other vehicles.

Given the trend of ever-increasing mandated safety, NHTSA may require extra strength in the A-pillar during the long design life of the next Wrangler. This does not mean that the Wrangler will need to go to a fixed, steel-skinned roof like the Cherokee, but it does mean major changes will be needed — if the rules change.

The current type of body may not be practical if the exemption is overturned. Therefore, to avoid stalling the project, I expect the first direction to be an open, fixed structure with removable panels of plastic and/or cloth material, and a fixed A-pillar that no longer folds.

My opinion is that the risk of a law change is great enough that Jeep must assume the worst case — that separate standards for convertibles will be dropped. This might mean a fixed roof (not necessarily a car-style steel-skinned roof) with the higher crush loads on the A-pillar, which eliminates several load cases caused by a removable or folding top, and minimizes the load cases for a convertible should that be required later on.

The Jeep JJ is an example of what I expect to be the configuration for JL. This means a body on frame, with the structure of the aluminum body designed to support the crush test standards for the conventional car, while still allowing an open top feel.

In this manner we can follow all the NHTSA rules by certifying the car to 216 without any exemptions.

There might be a way to soften the blow: making a “SkySlider” (Jeep owned trademark) fully opening top panel like the later Libertys.

How engineers meet the standards
To grossly simplify: When designing a body to meet standards, one positions a special mannequin (“OSCAR”), which covers 95% of Americans in size, and follows the swept space of its joint movements in a crash. The rules state the amount of impact, in force and intrusion, that will not kill the person. The designer must create a structure that will not deform so much as to kill off the occupants.

In addition, FMVSS 103, 104, and 111 all and the relevant SAE standards all show what and how you need to see out to safely operate your car.

In rough numbers (I am going to illustrate the problems, not solve for real numbers) you need to be able to support 25% of the gross vehicle weight, placed at a compound 45° angle, in all planes to the body, to pass the deformation test in compression. To do this, you can play with the:

A-pillar structure
•Windshield glass
•Front side glass
•Body mount and/or structure attached to a-pillar and frame (for body on frame) or subframe structure (for semi-monocoque or “unibody”)

Your limitations are:
•You cannot pass any structure through another panel (no cage tubes that go through or bolt through the dash panel/firewall)
•You can only follow the FEA (finite element analysis) load paths to minimize structure mass and complexity
•You are not allowed to split load paths and recombine into one path
•You can change thickness of materials up to 3x the thinnest section​

Now, overlay the Class A “show” surfaces from Design Office, along with the “master sections,” which show you the desired construction at key locations around the body.

Once these are in place, you get to start sweeping the sections into each other to determine the actual metal shape you will cut stamping dies from.

As you are building all these surfaces, you are also analysing the structure for adherence to the FEA load paths.....so you don’t end up with an oops and create a buckle condition under load, or a formability issue for fabrication.

Where you get a buckle, twist, or crack, you now have to decide on how to repair the issue. For example, can you stiffen the part by adding thickness to the base material — do you need a double panel to “glove” (this means be slightly smaller in size to completely fit inside your main panel), or can you add a separate piece to transfer the load elsewhere in the structure to another part to act as a bridge between the two parts that have failed?

You can also change the shape of the A-pillar itself, adding section height or width, but keeping the same thickness. You cannot intrude on any of the prohibited zones — commonly called DNE for “Do Not Exceed” zones.

You also avoid funky load paths like the split A-pillar used on the Fiat 500L, and extremely fragile glued quarter glass required to bridge between the dual A-pillars on each side, with all that attendant structure.

Using a fixed roof on the Wrangler allows time to be saved in the program, while not limiting options for later study.

As a side note, the removable doors cannot be crushed by the platen used for testing crush. The doors, if installed, must remain operable, so they cannot provide crush support in the load path. (The roof crush protection is not a bunch of round tubing, but would be mill shaped extrusions. A roll cage adds more weight without an equivalent stiffness increase.)

Just remember, regardless of how bleak the outlook, there is always a way to improve and advance. It may not be in a direction that people approve, but that does not mean you have failed.

Entire article with more photos and illustrations can be found on AllPar here:
http://www.allpar.com/SUVs/jeep/wrangler/future/convertible.html
 
I'm far from a Jeep purist as I just got into Jeeps so take what I say for what it is, just my opinion. But a fixed roof wouldn't bother me as much. Whenever I remove anything from the Jeep, it's normally just my doors. I like the shade the top provides while still being able to experience the "naked" feeling. That's why I sold my soft top and put my hard top back on with no intentions of buying another soft top.

I don't know if that slanted front will ever grow on me though...
 
As long as a Jeep can be modified to be personalized to my taste, to look and to act like a bad ass. If this can all be done with some wrenches while a buddy and I re-engineer everything and down a few drinks, I'm in! The rest is trivial to me.
 
Can't say exactly why, but that article reads like a rambling conspiracy theory website. "Because of A, we have B, C and D. However, when we factor in the space-time distortion of E, we arrive at the obvious conclusion: F."
 
If we are talking about crush forces as opposed to holding people in the vehicle, why not just put more of a real cage in right from the factory. I know, I know, it's more expensive. I sure would hate to see the removable top fall by the wayside.

Like I said in my Sharkey's Tip thread:

You can only make life so safe before you start taking away what it means to be alive.:naw:
 
If we are talking about crush forces as opposed to holding people in the vehicle, why not just put more of a real cage in right from the factory. I know, I know, it's more expensive. I sure would hate to see the removable top fall by the wayside.

Like I said in my Sharkey's Tip thread:

You can only make life so safe before you start taking away what it means to be alive.:naw:

I was thinking the same thing. Hell, even a rockhard cage from the factory would help with safety.
 
That's probably because Robert Sheaves is an engineer :crazyeyes: :D

Lol, probably. But mostly because I don't want it to be true.

I can see having large removable panels all over with thick pillars in place of roll bars. But to move to solid body with pano roof as the only option would be a bummer.
 
This is what's stopping me on trading in my Sport for a Rubi right now and being upsdide down 6k too. :doh:
 
If we are talking about crush forces as opposed to holding people in the vehicle, why not just put more of a real cage in right from the factory. I know, I know, it's more expensive. I sure would hate to see the removable top fall by the wayside.

Like I said in my Sharkey's Tip thread:

You can only make life so safe before you start taking away what it means to be alive.:naw:

Because they cant. Per the limitations that were listed a cage is not an option per the federal standards. Or thats how i read that.

The cage also adds weight which they also need to mitigate to be in compliance. From a practicality perspective the cage would be the best option for sure, but from a regulatory perspective the cage is the simplest and most effective fix amd therefore inadmissible.
 
JL....ya doesn't just roll off like saying JK, TJ, CJ...maybe in time.

So late 2016 is the time to buy one of the last JK I guess.

Worse case I guess it's aftermarket to help keep the "soft SUV" look out of my Wrangler.

Exhale........
 
If we are talking about crush forces as opposed to holding people in the vehicle, why not just put more of a real cage in right from the factory. I know, I know, it's more expensive. I sure would hate to see the removable top fall by the wayside.

Unfortunately, the limitations listed would prevent a real cage from being installed.
 
I have to admit. I will be very disappointed if there is no longer a removable top in the new Wrangler. Like Overlander said a more substantial roll cage from the factory would meet those NHTSA requirements.
 
Im gonna get flamed but here goes...I wish the Wrangler had an optional fixed roof. This would allow for 1/2 doors with pillarless glass, and that would be great for me. Still get the open air feel without the sun beating on my neck. The convertible option can remain for those that want it of course. Dare to dream.
 
Im gonna get flamed but here goes...I wish the Wrangler had an optional fixed roof. This would allow for 1/2 doors with pillarless glass, and that would be great for me. Still get the open air feel without the sun beating on my neck. The convertible option can remain for those that want it of course. Dare to dream.

Honestly that's probably coming as a weight saver if this is the direction FCA is going... wouldn't ya think?

Aluminum body with minimized metal engineering. Theyre already debating IFS... this is a potential idea. Who knows. Maybe we are retarded lol
 
Hope this doesn't happen, but it seems there are lots more folks lately who want to save us from ourselves. Glad I love the older iron so much and there's lots of it around. Besides, there's always the sawzall.:shock:

Edit: I do like the looks of this concept. Could possibly grow to accept it.
 
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