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Body on frame?

ABBB

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Can someone enlighten me to the benefits/legacy of body on frame? Ineos and every media outlet that writes about Ineos seem to mention the fact that the Grenadier is body on frame, and this seems to be major selling point to those disappointed that LR moved the Defender to a unibody construction. Why does automotive manufacturing (especially 4x4) now favor unibody, and what upsides and downsides are there to Ineos' choice to go body on frame?

PS - Looking to learn here, semi-new to 4x4 world - only experience with modern pickups - so take it easy/don't reply if you can't help but condescend to those who are less knowledgeable. To everyone else, cheers and TIA!
 

Spjnr

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OK so ill have a go at explaining! 

Unibody vehicles are generally lighter, more structurally complex, and quite strong in impacts for the weight, as the chassis and body are sort of one in the same. There are different styles of unibody, with some bigger vehicles incorporating sudo-ladder frames into the bottom of the body, but they are always one in the same. In this category you'll find:

Passenger cars (last 70 years give or take)
Sports cars
most new SUVs
crossovers
 
Body on frame vehicles are an older design, more mechanically simple, and often heavier. Almost all the structural strength of the vehicle is in the frame itself, leaving the body to be something that just needs to sit on top and provide a cabin, and rollover protection. This category includes:

95% of Pickup trucks
Lorrys (semi's)
Land cruisers
Jeep wranglers
Broncos
G-wagons
Most Commercial vans

The Arguments for Body on Frame design in off road vehicles are numerous, but the main ones include simplicity, strength, robustness and versatility.

Simplicity:
Ladder chassis are all pretty much the same. 2 lengths of (either box section or C section) steel, linked with numerous crossmembers. Off of this structure are attached all other parts of the vehicle; the body on top via mounts, the axles below via the suspension components, the engine, the bumpers at the front and rear, and auxiliary stuff like fuel tanks and what not. If your looking to replace or repair something, all these parts are very easily visible and very easy to get to.
In a Unibody vehicle, these components are bolted to the "tub" itself, and depending on the shape of the vehicle, often require inventive ways of attachment and thus can difficult to access.

Strength:
As stated above, Ladder chassis are steel. They're rigid frames propelled along with a body on top! This means when towing or hauling weight, all the stress is taken by the chassis. its very easy to build in strength, you just make it beefier. Think about the huge container hauling Trucks you see, all the weight is bearing down on those F*ck-off frames. In an off-roader, this means we can add weight to the vehicle and tow heavy loads (even reinforce the frame if need be), without worrying about the structure of the whole vehicle. In a Unibody this isn't the case, and the WHOLE vehicle has to be taking the strain.

Robustness:
Carrying on from above, Body on frame vehicles can take more punishment. Bumpers are attached to the frame not the body, meaning in small impacts, the force is directed down the strongest part of the vehicle, and not through the entire structure of the car. Also, although the chassis are rigid, theres always a degree of flex between the body and frame, meaning corrugations and impacts to the frame are somewhat isolated from the body. An impact for instance could damage the body badly, but could leave the frame intact, meaning you would be able to drive back to civilisation. In pickups this also means the tub can be isolated from the body, meaning heavy loads wont be twisting the body structure.  In a Unibody construction whatever happens to the vehicle will affect it in its entirety, meaning higher repair bills, and less chance of scavenging a wreck. Unibody Pickups have to engineer loads of strength into the cab to haul the same weight as BOF ones, and often just choose to drop the towing/payload figures.   

Versatility:
This is a biggy. when you develop a body on frame vehicle, you start with the frame, as all else works off it. Once you have this basic frame design, you can easily alter it to create variations on the same platform without having to completely start from scratch. Want a longer wheelbase version? no problem, stretch the frame and make a bigger body. Want a Ute? no problem cut the body in half and bolt a tray to the frame. Want a mobile elevated work platform (cherry picker)? no problem, bolt one onto the frame. You see where I'm going with this, anything is possible, not just from OEMs and skilled workshops, but average joes can customise BOF vehicles in their garage (I shortened the tipper back on my work Sprinter and bolted a toolbox to the frame). Winches and other hardware are easier to mount to a frame than a unibody, as are aftermarket bumpers. 
With a unibody vehicle none of this is possible without SERIOUS re-engineering, as you're affecting the structural integrity of the vehicle. Wondered why theres no New Defender pickup yet? its because Land Rover has to completely redesign the monocoque tub to create it, and that's a hugely expensive process. 

So all in all, for off road utility vehicles, body on frame is the way to go. They won't handle on the road like a unibody, they will no doubt weigh more, but at the end of the day, we're in the market for a Grenadier, not a Lotus Elise! The reason the market has swayed towards Unibody, is that none of these factors matter to the average person anymore. People favour Comfort, handling, economy (from weight savings) and price. Why build vehicles that are Bush proof  when they're just going to the shops and back. Unibody construction offers a far more car like experience, and that's what sells to the masses.

I'm sure I've missed a few bits, and feel free no challenge some of my points, but I hope that's of some help!

Steve
 

d1rty

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@Spjnr very well put.

The reason so many crossovers (some masquerading as SUVs) have gone to unibody (also called monocoque depending on where in the world you are from) is that they are generally lighter, and corporate average fuel economy standards are a bitch.  The lighter you can get your crossovers and SUVs, the better mileage you can squeeze out of them.

And an additional benefit for sporting cars is that you can generally get a much lower center of gravity with a unibody vs body on frame.  Not a huge concern with off-road, but higher CG can reduce side-hill capabilities.
 

ABBB

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@Spjnr - above and beyond! Thanks for laying all that out, as thorough as I could have asked for ?

What it leads me wonder is what will be sacrificed by going with this classic body on frame style? LR wouldn’t have ditched it if they didn’t think it would help them sell vehicles and generate pleased customers. I understand most of those customers aren’t spending days and weeks off road, so was the change of the Defender’s design just to encourage wider enthusiasm for the vehicle and sell more units? Couldn’t they have kept the Defender as it was for decades and pushed the Range Rover and Land Rover models to those who are inspired by car commercials but rarely explore off pavement? 

Thanks to @d1rty as well for the info and perspective!


 
 

d1rty

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[QUOTE username=AndyBeepBeep  ABBB userid=8889592 postid=1331962527]
What it leads me wonder is what will be sacrificed by going with this classic body on frame style? LR wouldn’t have ditched it if they didn’t think it would help them sell vehicles and generate pleased customers. I understand most of those customers aren’t spending days and weeks off road, so was the change of the Defender’s design just to encourage wider enthusiasm for the vehicle and sell more units? Couldn’t they have kept the Defender as it was for decades and pushed the Range Rover and Land Rover models to those who are inspired by car commercials but rarely explore off pavement? [/QUOTE]

My $0.02:

Corporate Average Fuel Economy (CAFE) and the equivalent European fuel economy standards.  When you factor in all the safety standards which have also been added, including door beams, all the electronic systems, etc, vehicles are going up in weight despite the transition to unibody construction.  And this is also why they (JLR) have gone with overly complicated engine systems (turbocharger plus supercharger plus hybrid?!) to eek out as much fuel economy as possible.
 

bakepl

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Interesting ownership summary in below link of new defender that discusses the limitations of a unibody design relating to rear axle loads and ability to upgrade.  Be interesting to see how the IG compares - I'm hoping it's considerably better in it's real world application of max tow weight, ball download, gvm, gcm, payload and axle loads, time will tell.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      https://www.youtube.com/watch?v=1gNUVWuqCu0 

    
 

3DDiY

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d1rty said:
My $0.02:

Corporate Average Fuel Economy (CAFE) and the equivalent European fuel economy standards.  When you factor in all the safety standards which have also been added, including door beams, all the electronic systems, etc, vehicles are going up in weight despite the transition to unibody construction.  And this is also why they (JLR) have gone with overly complicated engine systems (turbocharger plus supercharger plus hybrid?!) to eek out as much fuel economy as possible.
 

I suspect that grenadier hasn’t mentioned the fuel economy because of lot of what is said here. If JLR has to do that with all their cars imagine what the grenadier must be getting. One thing to consider is that the grenadier does get rid of a lot of tech so it could save some weight there. But a frame is pretty heavy. 
 

Stu_Barnes

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I get 13mpg on the school run (stop start la traffic) in the lr4 so any improvement on that will be great. Also the Land Rover takes premium fuel and the Grenadier will take lower octane so I was told at the la event. There’s no getting away from the Grenadier being a heavy vehicle. 
 

3DDiY

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I wonder how that works for some cars being released in countries and even states that have emission standards for new cars or MPG requirements. Its also not like Grenadier has any way to offset those with other cars in their line up that are electric or hyrdogen in their case. At least not yet. I recall car companies having to cap power to engines in those places that had those requirements. This is still a thing right?
 

Spjnr

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In the the UK theres allowances for small manufacturers, and those making commercial vehicles (grenadier fits into both categories). Id imagine theres similar loopholes in other countries.
 

CountyV8

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A monocoque held together by glue a la Range Rover is more difficult to repair so a small impact rights it off . They didn't tell you that at school did they .
 

emax

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A ladder-frame is unlikely to be damaged on non-capital impacts. A repair will mostly affect the box on top - which  is not as difficult to repair as a damaged monocoque. A damaged monocoque can even be the death sentence for the entire vehicle. 

An advantage of monocoques is in construction. Everything a car needs (gearbox, motor, zillions of mounting points, locations for electronics, and not to forget aerodynamic aspects) can simply be covered by the shaping of the monocoque. It so to say only needs a mouse-push at the computer to get a corner for the brake booster and done.

Well, it's of course more than a mouse-push, but you get the point. It is a bit like shaping knead.

Twenty years ago this was quite difficult as 3d-software didn't either exist or the hardware was simply priceless. Today, a medium sized company can afford tools like "Solidworks" or the like, and PC hardware is no longer a financial bottleneck. Thus, monocoques are nowadays much easier to construct *). And with the platform model in automotive industries (e.g. "modularer  Querbaukasten" it has become even easier.

However, monocoques are prone to hidden wet corners and often tend to have problems with rust protection.

They are more sophisticated in comparison to a body on frame concept, but as all sophisticated things they are more sensitive to design errors and maintenance- and repair-issues.

*) To be precise: Not really easier "to construct". But it is easier to add internal parts and features since this usually doesn't need a modification of the entire concept.
 

Geesh

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Heya -

Old school rock crawler here. I've owned and built ladder frames, axles, cages, etc., for my rigs (CJ's, YJ's, KJ's); both for fun and competition. I've also crawled in modified unibody Jeeps (XJ - Cherokee and Grand Cherokee). My experience taught me:

Unibody construction is good for on-road use & fire roads but requires stiffeners for more severe off-road and rock crawling use - and chassis flexure only gets worse the longer you crawl a unibody. Just open a door on a unibody rig with one wheel perched on a large rock; it can be hard to get it back closed. Ask anyone who has an ancient Landie: the body-on-frame configuration lasts over years of hard use. A ladder frame mounts to a chassis with through bolts using elastomer pads (bushes for you Brits). This allows for frame flexing separate from body flexing (mostly).

This is one of the many reasons that I'm so excited to get this vehicle.
 

DaveB

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I think they have identified their three main customer types and are not interested in fighting with all the main stream SUV manufacturers with monocoque designs. 
I doubt BMW would be too happy to supply them engines if they were targeting potential X5 customers.
Customer type 1 
Those who never go off road but want a vehicle that looks rugged and  "manly" 
These customers would buy a Defender or a G wagon but want some luxury and features, hence the leather option, carpet floors touch screen and apple carplay integration.
Customer type 2
People who want a workhorse that can tow a caravan, trailer, horse float or boat and can go offroad.
The ability to add on accessories and modify to carry a load but still be a daily driver as well. 
The dual cab ute will be a smash hit in Australia as a work/play vehicle. 
Body on frame is essential for this. 
Customer type 3
Companies looking for a work fleet
Mine sites in Australia use heaps of Toyota vehicles.
These are often cab chassis/tray back vehicles so the body on frame is essential to allow as much versatility as possible.
These vehicle also cop a lot of abuse from drivers and the environment they are in.
They need to be serviced by company mechanics onsite and in workshops. 
I think this is their volume market but very price competitive. 
I have no doubt INEOS Australia will be targeting this with the basic 2 seat Ute version and a cab chassis version of the ute/pickup which will be on a longer frame than the wagon. 
 
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