Advantages of a unibody???

[ChevyKev]

in akxj's thread about his one tons he mentioned strengthening his frame -
which was the second thought I had after thinking "cool" to 1 tons under an xj.

Which brought me to lead his thread off topic - so I am moving it here:

I asked:

WHY A UNIBODY IN THE FIRST PLACE??? (Not you, JEEP) What, if any, is an advantage to unibody? Expecially from a company like Jeep that has their trail rated logo and off-road roots? Does it really cut down on costs? Weight? Handeling charateristics?

Not meaning to thread jack, but I see no substancial benefit. And if no benefit, then why not a solid frame? And if a solid frame - you wouldn't have to be reinforcing it.

So is there a substancial positive characteristic to unibody vehciles? I'm not trying to put down the company, the vehicle, or anyone's choice to build one - I honestly want to know if there is an advantage that I haven't thought of.

Educate me!

Which lead Kyle to respond with :

Lighter, more ground clearance and cheaper all come to mind.

Solid frames need to be reinforced too. Go flex out your plow truck and measure how much the cab and bed move relative to each other.

By the time you brace up a standard frame SUV with a roll cage and by boxing the frame, you end up remarkably similar to what you have in a braced XJ. If the end result is the same anyway, what's the problem?

DISCLAIMER: I like XJ's. I know several people that have made thes into very serious wheeling vehciles. I have owned several in the past, but mostly as DD family vehicles which thee unibody handles very well. This is not a slam on anyone for owing or building an XJ.

However, I don't like Jeep engineering on several points. The unibody on a vehicle that has the Jeep name - which is fairly synonymous with off-roading is one of those engineering designs I think are questionable. I'd like this thread to discuss the use of unibodys - pros and or cons. Don't even get me started on bolts requiring E-sockets!:pissed:

[ChevyKev]

Kyle, let me pretty much COMPLETELY disagree! :pbbt:

Lighter, more ground clearance and cheaper all come to mind.

Lighter - ok, maybe - how much really??? :confused:

More ground clearance? :tease:4 inch gain for 3.5 feet maybe. Did Jeep really engineer this vehicle to be a unibody for ground clearance reasons? This to me sounds ludicrous. Why would they need ground clearance? Speed bumps in shopping malls? These vehicles can be built into incredible wheeling rigs, but they were not designed that way from the factory. Thus it is incredibly highly unlikely that ground clearance played into their decision making.

Cheaper? hifty: This is the only logical conclusion to me. less metal, and an integrated design may equall less material costs and less assembly time and cost. Now, while on 1 or 2 vehciles this may not add up to much, multiplied by the thousands or millions of these vehicles to be made = huge savings. From a business standpoint, this makes some sort of sense.

Solid frames need to be reinforced too. Go flex out your plow truck and measure how much the cab and bed move relative to each other.

This argument makes no sense - while yes, the frame twists some, the body is designed to flex with the frame. So you don't have the same issues as a unibody vehicle where the frame isn't as supportive and the body twists more. You're comparing apples and thermostats here. Most solid framed trucks that are made into serious wheelers take little to no strengthening (except around the chevy steering box:doh: ) because the body flexes with the frame. [and I have flexed my plow truck before, thank you!]

Also, how many TJ/CJ/YJ's need frame strengthening when making it a more capable rig? We aren't talking about a vehicle the length of a pickup - we are talking about an XJ.

By the time you brace up a standard frame SUV with a roll cage and by boxing the frame, you end up remarkably similar to what you have in a braced XJ. If the end result is the same anyway, what's the problem?

Thank you for making my point! :expert:

My question was Jeep specific - Jeep being somewhat synonymous with off-roading. So why put a unibody under a vehicle with the off road name, that when you make it into a more serious off-roading vehicle you HAVE to do the work yourself to make it as strong as a solid framed vehicle from the factory?

What's the problem? all the extra work to get a similar result in a vehicle that is supposed to be trail rated in the first place.

[sevenslats]

The reason I asked akxj what he did to reinforce the frame wasn't flex issue. It was a sheetmetal tearing away from the wieght of a wider axle with heavy tires.

[naturalbornmudder]

In my own opinion, th eonly benefit to a unibody is the XJ/ZJ that is attached to it.

I do not like unibodies and I do not see any benefits to it as opposed to a frame

[Jamakeit]

I think when Jeep wanted an suv which could still offroad like a waggy and fit 5 people but drove more like a car the uni-body was the creation. Less truck, more car, still Jeep, and thus the "soccer mom was born"......I think it is a great product for it's design, heck I own one too, but to be built really big it does need attention, as all rigs have their shortfalls.

[Advent]

More ground clearance? :tease:4 inch gain for 3.5 feet maybe. Did Jeep really engineer this vehicle to be a unibody for ground clearance reasons? This to me sounds ludicrous. Why would they need ground clearance? Speed bumps in shopping malls? These vehicles can be built into incredible wheeling rigs, but they were not designed that way from the factory. Thus it is incredibly highly unlikely that ground clearance played into their decision making.

I'm sure it played at least a minor role. The jeep certainly called for more ground clearance than it's stable-mate the Eagle.

Look at how nicely everything tucks up under an XJ. It's very similar to a hummer in that it's all up inside the body area. Those extra 4" can help quite a bit.

This argument makes no sense - while yes, the frame twists some, the body is designed to flex with the frame. So you don't have the same issues as a unibody vehicle where the frame isn't as supportive and the body twists more. You're comparing apples and thermostats here. Most solid framed trucks that are made into serious wheelers take little to no strengthening (except around the chevy steering box:doh: ) because the body flexes with the frame. [and I have flexed my plow truck before, thank you!]

Also, how many TJ/CJ/YJ's need frame strengthening when making it a more capable rig? We aren't talking about a vehicle the length of a pickup - we are talking about an XJ.

My point wasn't that the body and frame should flex together. My point was that they shouldn't flex at all. Flex negatively effects the suspension's ability to do it's job, side to side flex can bind steering (or rip off steering boxes), and it all ends up leading to metal fatigue (though steel is pretty good at not getting fatigued).

As for TJ/CJ/YJ frame strengthening...That's one major benefit of tying a roll cage into the frame. It ends up bracing the heck out of it! It's like going from 4" frame rails to 5' frame rails. Big difference.

By the time you've added that cage to a fully framed rig, you've made all that steel on the underside unnecessary. Lots of buggies down south cut the frame out completely for more clearance and just integrate the roll cage (thus making a tube unibody).

My question was Jeep specific - Jeep being somewhat synonymous with off-roading. So why put a unibody under a vehicle with the off road name, that when you make it into a more serious off-roading vehicle you HAVE to do the work yourself to make it as strong as a solid framed vehicle from the factory?

But even on a solid framed rig that's going to see extensive off roading you generally want to put a roll cage in. As I said above, that makes the extra few hundred pounds of steel unneeded.

Look at a lot of old half ton pickup trucks that have been beat on. You can tell that the frame is slowly bending downward right in the middle. XJs are no different; They're fine until you beat on them. Then you need to stiffen them up a bit. The simple fact of the matter is that most of the vehicles we use in our hobby simply weren't built to handle the ever-increasing stresses we throw at them.

What's the problem? all the extra work to get a similar result in a vehicle that is supposed to be trail rated in the first place.

Did the XJ ever come with a Trail Rated badge? I thought it was discontinued before that was even started :lol:

From a safety standpoint it's probably better that you have to focus first on bracing the rig up. How many people build up big tall rigs and put the roll cage in last?

[sevenslats]

http://en.wikipedia.org/wiki/Unibody

Monocoque design is so sophisticated that windshield and rear window glass now often make an important contribution to the designed structural strength of automobiles. Unfortunately, when a vehicle with a unibody design is involved in a serious accident, it may be more difficult to repair than a vehicle with a full frame.

[ChevyKev]

I'm sure it played at least a minor role. The jeep certainly called for more ground clearance than it's stable-mate the Eagle.

BAH-loney! the XJ already had more ground clearance due to the suspension.

Look at how nicely everything tucks up under an XJ. It's very similar to a hummer in that it's all up inside the body area. Those extra 4" can help quite a bit.

And the suspension bone is connected to the sub-frame bone... I will state again - this results in very little ground clearance in only one spot of the vehicle. You still have the sub frame sticking down in front and back. result is minimal increased clearance, and I doubt was a serious consideration from the engineers during the design phases.

My point was that they shouldn't flex at all. Flex negatively effects the suspension's ability to do it's job, side to side flex can bind steering (or rip off steering boxes), and it all ends up leading to metal fatigue (though steel is pretty good at not getting fatigued).

WHAT??? For a rock buggy, maybe - but tell me why we have rubber or polyurethane bushings between body and frame? To allow - FLEX. Over flexing may negatively effect steering, mostly this is minimal, and designed for a purpose. Some ability to flex is needed to not over-stress things, such as how suspended walkways, bridges, and sky scrapers are designed to be flexible - if rigid they would fail quicker.

As for TJ/CJ/YJ frame strengthening...That's one major benefit of tying a roll cage into the frame. It ends up bracing the heck out of it! It's like going from 4" frame rails to 5' frame rails. Big difference.

By the time you've added that cage to a fully framed rig, you've made all that steel on the underside unnecessary. Lots of buggies down south cut the frame out completely for more clearance and just integrate the roll cage (thus making a tube unibody).

We're not talking about buggies. We're talking about capable rigs and the difference between solid frames and unibodies. My point is you shouldn't NEED to add frame strengthening or a full roll cage for frame strength to have a capable off-road vehicle. Roll cages mostly are not to strengthen the frame, but protect occupants. The reasoning for hooking into the frame is to strengthen the cage in event of a roll, does it strengthen the frame? Sure. Is that most folk's purpose? Not those with solid frames.

But even on a solid framed rig that's going to see extensive off roading you generally want to put a roll cage in. As I said above, that makes the extra few hundred pounds of steel unneeded.

Again, for safety more than frame strength.

Look at a lot of old half ton pickup trucks that have been beat on. You can tell that the frame is slowly bending downward right in the middle. XJs are no different; They're fine until you beat on them. Then you need to stiffen them up a bit. The simple fact of the matter is that most of the vehicles we use in our hobby simply weren't built to handle the ever-increasing stresses we throw at them.

Compare a 1/2 ton truck with solid frame and a unibodied vehicle, abused similarly, and tell me which one suffers quicker and more. In most cases the unibody will be in much worse shape quicker. So again, on a vehicle with the Jeep name....

Did the XJ ever come with a Trail Rated badge? I thought it was discontinued before that was even started :lol:

True - but the theory was there before the badge. :pbbt:

From a safety standpoint it's probably better that you have to focus first on bracing the rig up. How many people build up big tall rigs and put the roll cage in last?

Hey - quit talking about me!

[ChevyKev]

I think when Jeep wanted an suv which could still offroad like a waggy and fit 5 people but drove more like a car the uni-body was the creation. Less truck, more car, still Jeep, and thus the "soccer mom was born"

Here I think is the real answer to why - underlined in bold.

More car like handeling + less cost I mentioned earlier. :whistle:

I think it is a great product for it's design, heck I own one too, but to be built really big it does need attention, as all rigs have their shortfalls.

Absolutely. As well, I agree that they do well for their design, until you build them "really big"

[naturalbornmudder]

a chebby guy and a toy-o-cruiser guy argueing about Jeeps....Bahahaha!

[Advent]

WHAT??? For a rock buggy, maybe - but tell me why we have rubber or polyurethane bushings between body and frame? To allow - FLEX. Over flexing may negatively effect steering, mostly this is minimal, and designed for a purpose. Some ability to flex is needed to not over-stress things, such as how suspended walkways, bridges, and sky scrapers are designed to be flexible - if rigid they would fail quicker.

Skyscrapers and bridges are also designed to last for a hundred years, and if they flex 6" over a thousand feet the net effect on any given small part is minimal. Contrast that to 6" over an 18 foot vehicle designed to last 10 years.

The reason for rubber and polyurethane bushings is not for flex at all. It's to isolate the passenger compartment from road noise.

We're not talking about buggies. We're talking about capable rigs and the difference between solid frames and unibodies. My point is you shouldn't NEED to add frame strengthening or a full roll cage for frame strength to have a capable off-road vehicle. Roll cages mostly are not to strengthen the frame, but protect occupants. The reasoning for hooking into the frame is to strengthen the cage in event of a roll, does it strengthen the frame? Sure. Is that most folk's purpose? Not those with solid frames.

Sure, frame strength isn't most folks' reason to put in a cage. But it helps. Look at how many full framed rigs have to do significant frame repairs after the frame has cracked? If they had a stiff cage it wouldn't have happened. With a unibody design the damage is visible sooner and progresses. With a full frame it's visible later, after it's nearly catastrophic.

Compare a 1/2 ton truck with solid frame and a unibodied vehicle, abused similarly, and tell me which one suffers quicker and more. In most cases the unibody will be in much worse shape quicker. So again, on a vehicle with the Jeep name....

It was probably a bad example, apples to oranges and all that. But the fact remains that if you beat a stock vehicle's frame it will wear out, whereas if you brace it first it very well might not.

Hey - quit talking about me!

I didn't really mean that as a jab at you, I've just started becoming much more risk-adverse when it comes to my safety. In my case that means I'm moving the new 'cage, seats, and harnesses up from near the bottom of the list to near the top. It's only money

[Advent]

a chebby guy and a toy-o-cruiser guy argueing about Jeeps....Bahahaha!

The worst part is that I'm actually arguing on jeep's behalf.

How in the heck did that happen?!

[ChevyKev]

a chebby guy and a toy-o-cruiser guy argueing about Jeeps....Bahahaha!

:bat::troutslap:

[ChevyKev]

The worst part is that I'm actually arguing on jeep's behalf.

How in the heck did that happen?!

Finally he realizes his logic flaw! :tease:


My point - to restate the stated - Solid frames are stronger than unibody "frames".
Yes the solid frames can wear out - but will do so much less, and last longer before they do, if abused in similar ways.

Unibody's offer little positive to a serious 4x4 - and ground clearance is minimal.

So why would JEEP - a company known for off-road vehciles build a vehicle with a unibody?

Ah - back to the less truck more car - which makes my point.

Again I ask - what actual benefit besides minimal ground clearance does a unibody offer?

[ChevyKev]

The worst part is that I'm actually arguing on jeep's behalf.

How in the heck did that happen?!

How you ask? Because you'd argue with a stop sign!

[Advent]

Again I ask - what actual benefit besides minimal ground clearance does a unibody offer?

Well, if nothing else, you can pick up a mid-90's 4x4 with solid axles for $1500.

How you ask? Because you'd argue with a stop sign!

And like most other arguments I get into, I'd probably lose! :lol:

[INDIANOUTLAW]

Again I ask - what actual benefit besides minimal ground clearance does a unibody offer?

well it's just my opinion but owning a unibody gives the owner lots of pratice welding on thinner materials. besides that i have to agree w/ kev i think that the unibody design is way cheaper to manufacture all the pieces are easily stamped and welded together, and i'd be willing to bet that it ends up being less bolts too. not that i have any "real" problems with the unibody other than the fact if you come down on it you'll tear it all up it is nice having a frame to keep your undercarrage protected a bit.

[akdsmer]

Don't forget that a unibody allows the engineers to design "crumple-zones" to allow for reasonable body velocity degradation. It's difficult to do that with two big pieces of metal sticking out the front!

[Snowman]

That would be my biggest guess, better crash test ratings.

[TJVigilante]

That would be my biggest guess, better crash test ratings.

HE'S BACK!!! :p

Now I can change the month on the calendar.