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Why would a manufacturer use a ladder frame in a car?


#1

Ready for a wall of text? Me neither, but here it comes anyway. You’ve been warned.

So, I watched GETD Ep16 [The Triggering] (the trolling?) and I’m going to try not to get caught up too much by my own emotional attachment to cars and simply try to correct what I consider to be misconceptions, or maybe just tell another side of the story.

Backing up, I’m first going to reference GETD Ep01 (1955 Sport Coupe). I feel like in a tycoon game that has a timeline, historical accuracy should be a thing. Or at least, if I try to recreate a “great car” from an era, I shouldn’t be punished for it. Automation disagrees. Killrob here builds a sports car with dual A-arms at all four corners and a monocoque chassis. Let’s look at what RL manufacturers were building in 1955.

“Space Frame is not really a thing, although you could argue that this one was being made in a shed” Killrob, GETD Ep01.

This is the frame from a Mercedes 300SL, Mille Miglia Winner and, imho, one of the most advanced cars of the 1950s. It is true that not many road cars were built with space frames, but not because space frames are low tech. Check out the beautiful Maserati birdcage. They’re labor intensive to build and not that practical for passenger cars.


Jaguar road car

Lister-Jaguar-Twin-Tube-Frame
Jaguar sports racing car

Jaguar XK120 road cars of the era were using leaf spring rear axle, Ferrari a DeDion (beam axle), the Mercedes a swing axle.

So Killrob has built himself a car whose tech exceeds the best high-end cars of the era. It’s expensive, right?

Nope. It scores well into sport budget. And how would a 1950s Ferrari, Jaguar, or Mercedes score in Automation? Ugh. Sometimes it’s difficult to know what is a good “design decision” is without understanding Killrob’s interpretation. Watching the YouTube stuff has helped me some, but it’s far from intuitive.

Anyway, on to misconceptions and other meanderings.

“Ladder frames are wobbly as fuck” -Killrob, GETD Ep16.

Not necessarily. Boxing the rails, and adding crossmembers and reinforcements can make a ladder (body on frame) frame as stiff as it needs to be, at the cost of weight. And yes, this design is not as efficient in terms of interior space. Compared to a spaceframe, however, it does allow for the inclusion of doors. Looking at sites like Art Morrison chassis, Chris Alston chassis works, and so on, somewhere I read a claim that a ladder type frame can be made to equivalent stiffness compared to a space frame for a weight increase of 5-10%. Check out the stuff Icon is using under their custom builds, those frames are beefy. Still don’t believe a ladder frame can have decent rigidity? This is basically a Chevy truck advertisement, but it shows a modern example of a very stiff ladder frame.


I don’t advise trying that with your Audi. Also, anyone who’s driven a modern American truck can attest to their comfort and driveability, in spite of their size and utility.

Just for funsies, here’s a Chevy ad for their frame from 1935. It does a good job of simply explaining what’s required of a car chassis.

Which begs the question, how much stiffness is needed? The answer is not as simple as what I’m going to put forth, as required stiffness depends on use. For racing cars, stiff enough to support the incoming loads from the suspension without appreciable twist. So it will depend on the incoming loads, heavier race cars will need stiffer chassis. However, in a race car, extra weight is unwanted. As a rough guide, Formula SAE engineers recommend somewhere around an order of magnitude greater than incoming forces, you won’t really notice improvements in chassis stiffness higher than that.

Then why do only trucks use ladder frames today?

Well, a few reasons come to mind. Crashworthiness: You don’t want a stiff frame in a collision, you want one that crumples. Yes, really. Monocoques are better at dissipating force (crumpling) in some directions while being stiff in the directions your suspension requires. Fuel Economy: Ladder frames are heavier, which costs fuel, and require a higher profile, which hurts aero. Are monocoques inherently quieter, or less creaky? No, but I’ll get to that.

I will grant that Citroen (and others, even ‘Muricans) were using monocoques (unit body) in the era (and earlier), so I’m going to try to address the question: Why wasn’t everyone?

Let’s look at early monocoque design.
citroen
Citroen


1960 Chrysler. Both are monocoques, even modern monocoques seldom look as beefy as that French beauty.

Re: 1960 Plymouth unit body
Lanny Knutson wrote for the Plymouth Bulletin:

There was a frame, however - a subframe, bearing the engine and “Torsion-Aire” front suspension, that was bolted to unitized body. This arrangement allowed the front fenders to be more easily removed for repair or replacement than those of the completely unitized Rambler. … One of unitized construction’s drawbacks is that no sound insulating material can isolate the body from the frame, bringing road noise into the cabin. To counter this problem, Plymouth developed extra large rear spring bushings, a new exhaust system hanger, and a driveshaft designed to reduce high-speed hum. Special sound deadening fiber matting and liquid-applied coating contributed to making what could have been “riding in a tin can” into a pleasurable experience of traveling in a car far quieter than those of then-conventional construction. And, of course, the engine was mounted on its own frame, separated from the body by the usual sound deadeners.

With its 1957 models already rusting out, Plymouth had to confront the rust problem in a big way. The spectre of a rusting-out unibody with no frame to hold it together was simply too scary to contemplate. A series of six chemical sprays and seven dips into chemical baths plus four coats of paint prevented rust where its damage could be worst - on all those structural inner beams. The wheel wells, exposed as they were to road salt, still proved to be subject to rust, however.

quoted from Allpar

“We’re not using a ladder frame, that is fucking stupid.” -Killrob, GETD Ep16.

Ladder frames are inherently better at isolating the passenger compartment from engine and road NVH. Extra mushiness has to be designed into the suspension, and lots of sound deadening used to counter this. In my opinion, this is the biggest reason they continued to be used for so long (in passenger cars), even after monocoque technology had been proven. And, in my own head, why they’re a viable design choice for luxury markets prior to fuel economy and safety regs. Or, in Automation, for markets who care more about NVH than safety or fuel economy. Like Muscle. Or for markets that have a high preference for new sheetmetal, which requires far less engineering effort than on a monocoque, both in terms of design and production.

Nor is rust or metal fatigue as big an issue for a ladder frame, whereas it threatens the structural integrity of a monocoque. Which is why Chrysler went to such efforts to rustproof at a time when no one else did. All those chemical baths, extra paint, even wax sprayed on the bottom …and they still rusted.

Bear in mind also the much greater labor cost in stamping and assembling a monocoque. In an age before robotic welders, DeSoto claimed 6000 spot welds in their monocoque. Plymouth claimed 5400. That’s a lot of welding!

So why use Ladder Frame? It’s cheap, sturdy, durable and isolates the cabin from road and engine NVH.

A caveat: Yep, American ladder frames were pretty flexy. They got much better with boxed frame sections, but not as good as, say, Rolls Royce. When I drove a tow truck, I once hooked up a late 50’s Rolls. The main rails on that frame were enormous, maybe 4”x6” and made of super heavy gauge steel. Not a performance application, true, but ladder frames aren’t just for trucks.

edit to add another pic to break up this wall of text :slight_smile:


Sidebar: If you go to car shows where American cars are featured, you can prove this to yourself. Ride in a full framed car like a Catalina (in good condition), then find a nice monocoque car to take you for a ride. I’ll use the example of Mustang or Camaro, though they’re not “quite” monocoque (they use two frame stubs bolted to a central pan,insulated by bushings between rails and pan, with shock/strut loads supported by the towers- possibly the flexiest thing ever; not really represented in Automation -semi spaceframe perhaps but this is only available in aluminum post 1990ish, and monocoque is closer as the rockers bear much of the torsion) they’ll do for our purpose. Compared to the full framed car, those things rattle and creak much more. And this condition is only exacerbated by time, metal fatigue, wear on the chassis, deterioration of bushings, and rust. Find two cars of equally ratty condition and find out for yourself. Shelby had to reinforce the heck out of the Mustang to make it a competitive race car, whereas the ladder frame Corvette needed no such attention. Another interesting comparison in the mid 90’s is the Buick Roadmaster vs. Park Ave. Built for the same market, by the same company, at very similar price points, the Park Ave outperformed the Roadmaster in every measurable way, except maybe NVH. To me, the Roadmaster “felt” better. But this could just be emotional bias, I was 16 working at a Buick dealership and the Roadmaster did awesome burnouts.

Does anyone else want to see more nuance in chassis?
X-Frame, perimeter frame, backbone, subframe, and a partridge in a pear tree.


#2

Body on frame smooth as ever:


#3

Some chassis were designed to flex to aid articulation
unimog


#4

My guess is that the devs will argue that all the real world engineering solutions can’t be accounted for, and that genericising ladder as flexy and bad, and unibody as good, is to keep dev time down, instead of adding reinforcement sliders, etc.


#5

This is an awesome writeup. While I don’t intend to necessarily take anything away from it, it certainly did inspire me to make a good pickup truck for the first time. :grin:


#6

Indeed a good write up :slight_smile: thanks for sharing. Also kudos for taking the emotion out of it, which is what I was trolling in that video (Ep.16). While I don’t see how you have corrected any of my statements, you do show a fair bit of nuance that could / should be added to them were it in a different kind of video. Some of what I say in those videos is very much in a specific context:

  • A company with an unknown prior history of building cars
  • No historic burden or car cultural norms to cater to beyond what the demographics require
  • The true cost of tech is difficult or impossible to see because engineering time and production units are not considered in the scoring of the demographics, which only look at the car being available right in the moment. I try to stay somewhat true to what would be feasible though.

For instance “It’s expensive, right? Nope. It scores well into sport budget.” very much is due to the latter point, and it would be unfair to blame me or the game for this in the context of the sandbox. Spaceframe is not high tech, that is a misrepresentation. Space Frame is not really a thing because it is very labor intensive to produce and cannot be mass produced, which means you get very low production output. Hence why you could perceive it as high tech (only the lowest production volume cars would have that) even though it is low-tech stuff.

Just to clarify, I do stand by everything I said :slight_smile: but the way I express it is to deliberately (in that video at least) piss off the “right” people :stuck_out_tongue: those who comment under every video how I’m doing it wrong because it is not conforming to their narrow-minded, Murrica-centric view of cars :smiley:

Cheers!

Edit: Ohh, and of course there are plenty of situations where using a ladder frame makes perfect sense :slight_smile: that is out of question. Muscle cars are not one of them though ;D (without the very specific situation manufacturers in the US were in at the time).


#7

Just saying…
I have owned Chevrolet Caprice Classic, STW -87 which is classic, American “body on frame” “Fullsize” wagon.
I have also owned Ford Sierra wagon -86 which is unibody European wagon, not the largest car but essentially they are catering to same market, and there was nearly no difference on price when sold new, at least where I live.
From those cars, if I would want a “Fast” “Well handling” “economical” car I would definitely pick the Ford, as first time it started feeling comfortable to drive was well past higest legal speed.
How ever if I would want “spaceous” “comfortable” “family” car I would withuot a second thuoght go for the Chevy.

Sure there is lot of other differences. such as.
5.7l V8, 3 speed automatic vs 2.0l I4 5 speed manual,
Chevy is notably larger car overall,
Ford is slightly more ergonomic,
Ford is more economcal (Not that much actually)
But overall I concider the Chevy with it’s solid rear axle, and ladder chassis overall BETTER car


#8

There’s two major issues that I have with ladder frames in the current version of Automation. The first is related to a broader issue: Safety is massively overrated in nearly all markets. Even in Light Sport, it’s almost always better to choose Advanced Safety. Similarly, ladder frame has a huge safety penalty compared to monocoque, making it a universally uncompetitive choice in all markets.

Secondly, for whatever reason, ladder hurts utility rather than improving it. It seems that it causes towing speed to be significantly reduced for some reason. This, combined with the loss of the 20% utility bonus from Kee, makes monocoque better than ladder for utility vehicles.

I’d like to emphasize that the cost benefits of a ladder chassis are actually quite well modeled in Automation; they are noticeably cheaper to produce and engineer, especially in the earlier years where overall PU/ET is lower. I think that if you address the two issues above, and maybe add in a small comfort bonus from the NVH advantages, ladder frames will become logical choices in certain markets and eras (compared to now, when there’s no reason to ever choose ladder).

Random side question: is chassis stiffness modeled in the BeamNG converter or no?


#9

One of the issues could be that when the tire load capacity is limiting overall load capacity of the vehicle, then ladder chassis won’t help that fact and indeed make the car worse. Have you considered that possibility where you observed that?
Certainly we will have to do more balancing, but it really needs to be done in context, sandbox is not the place to get things like costs, production, and engineering right. :slight_smile: Safety importance will be readdressed in balancing, as that is currently static but will be made dynamic over the years, currently it only adheres to modern standards.
Yes, chassis stiffness carries over to BeamNG a little bit.


#10

I would also add that safety is massively overrated for monocoque in the early years. Before computer aided design could do its magic, many monocoque cars were eggshells that were less durable and less stiff in all the wrong ways. People who swap modern power plants into 1st gen Ford Falcons and Mustangs are painfully aware of this and have to add frame strengthening rails in order to keep from cracking their windows.

Cars were death traps in general before computer aided design and finite element analysis could allow for properly engineered crash boxes. So the safety “benefit” of unitized construction is negligible before the mid 1970s. Now, as Automation buyers supposedly exists in its own universe, I am willing to accept they might have different tastes for safety. But 1960s? Monocoque? Safer? :man_shrugging: Probably not the way most manufacturers were building them ie with a complete lack of perimeter frames. Ergo, I believe ladder frames are a quite comparable choice in the early years.

Now that all being said, I can understand and even appreciate Killrob’s propensity to poke fun at how us Yanks deify our cars without much in the way of proper context. They were just cars – nothing more and nothing less. You have to understand the rationale for their design and I don’t think most people do. They get spoonfed BS about how classic Americana is golden and then refuse to accept that it could at very least be rational to design cars differently.


#11

Point taken, and maybe this is what I have a hard time wrapping my head around. In 1955, space frame was high tech. In this universe. Or maybe I’m looking at tech the wrong way? 1955 was Ferrari’s first year using a space frame chassis in GP/F1 with the D50 when Lancia bowed out. Most of the field used space frames. In sports car racing, there was only Mercedes (the 300SL was using GP chassis tech), Maserati’s Tipo 61 (sports racing car) was considered a revolutionary design at the time (1959). I’ve always considered sports car racing, and especially GP/F1 to be the apex of automotive technology. These cars weren’t being built in sheds -at least in this universe. F1’s first monocoque came along in '61 with the Lotus 25. But perhaps this mindset is wrong as well, since we are mostly only dealing with road cars.

Formula SAE is a series for college students to design a spec formula car, and have it judged by engineers. Many of these cars are still using spaceframes, despite the fact that monocoque is allowed. These are not low tech space frames, either. Most use pushrod suspension setups, some use the engine or trans as a stressed member, most are built using CAD and finite element analysis tools… overall speeds are pretty low for these cars (relatively speaking), but they are also judged on fuel economy as well as track performance. It’s a pretty cool series that encourages creative design solutions. Again, these cars are much more advanced than what would come out of a shed.

Old tech is not necessarily bad tech, or irrelevant tech, or even low tech imho. We’re still using the same old, stale, round wheels. In the case of a space frame, a round tube will always be stiffer than an equivalent box section. But I digress, I agree that it has no place in road cars and said as much in my post. I don’t think I’m confusing low production for high tech, though.

I probably need to focus more on stats of choices, and less on history, given that Automation takes place in an alternate universe. I should stop expecting it to be a parallel universe.


#12

Early Camaros had a bolted on subframe but Mustangs were completely unibody…


#13

Thank you for the correction.

edit to add: I was looking at this, assumed those were stubs.


#14

The Volvo 140 series unibody, released in 1966, was good enough to survive into the 1993 Volvo 240 with only minor alterations, with many experts still regarding the 240 as one of the safest cars in the world when it ended production, so that’s probably an early example of a good unibody. But before that? Maybe Mercedes that was a pioneer when it came to crumple zones, but I would think that many early unibodies is either beefed up everywhere and too stiff to crumple, or too weak and will fold like tinfoil in crashes. So you’re probably right…


#15

Demonstrated quite acutely here:

Metallic monocoques are very rare in purpose built race cars though, partly due to complex bespoke tooling being all but required (The sheet metal has to be made complex to be stiff) and partly because monocoques lose a lot of their advantage when interior volume requirements shrink.

Oh wait, I forgot a detail: space frames for race cars will often have some variety of panels affixed between the tubes for reinforcement and for intrusion protection, traditionally this has been aluminum honeycomb but it seems carbon fiber is starting to show up in this role now as well. They sometimes make space frames look like monocoques.

I also might contend that, with purely metallic chassis, a space frame is more rigid full stop, after all you don’t see many “roll coques”. Vector, for instance, used a space frame at the center of their chassis with monocoque subframes as crumple zones.

Wait I might already be eating a bit of crow, seems Formula 1 cars were aluminum monocoques for a while there, but they weren’t really the same sorts of monocoques as used on street cars. Earlier ones were almost like stressed skin airplanes and later ones were made largely out of aluminum honeycomb.


#16

True, but note that you are now comparing cars with 50 year difference in technology.
If you would reduce that, to let’s say Opel Senator from late 70’s to early 80’s


I think also Holden used this chassis, not sure…
Anyhow, if the collision would happen with Impala and Senator, Sure the impala driver would definitely be injured or might die, How ever, The impalasfront bumper would be roughtly where driver seat is in that senator. Well… that might have been slight exaggeration, but you get my point.


#17

Also, the 58-64 Chevies (along with many other GM cars from the 50s and 60s) used an X-shaped frame that is extra horrible in offset crashes. However, sure, there was a crash not far from me some years ago where a 1963 Pontiac Bonneville (which, IIRC, had switched to a perimeter frame) and a BMW E46 hit each other at high speed in a manner like this, offset corner to corner, and the Pontiac looked about as bad as the Chevy, however, I think the speed was higher, judging by both the speed limit at the road, the damage to the E46 (passenger compartment compromised, and an E46 shouldn’t be much worse than the Malibu I think) and the fact that even the E46 driver died (though I don’t know if seatbelt was used), so they probably can’t be fully compared.


#18

Is it wrong that I feel worse for the classic Chevy than I do for the dummy? Yes, NHTSA, we know that 50 years of tech has made cars safer. Did you need to destroy a classic Chevy to prove it? The dummy wasn’t even wearing a seat belt… Please, please, please wear seat belts, people. It makes so much difference. The airbag is not designed to save you if you’re not belted.

I have a feeling NHTSA picked an X Frame car for exactly the reason @Knugcab stated. Had they rammed the new car against the Rolls pictured above, both drivers would likely get injured but the Rolls would be repairable. I once had a discussion with a body guy about whether new cars were stronger than old ones. The disconnect in that discussion was that my concern was for the driver, his for the car. “But you’d be speared and killed by the column,” I argued. “So what?” he replied. “We’d just hose you off the dash and sell the car to the next guy.”


#19

There is another thing that was horrible in front steer cars (like an X-frame Chevy) in the pre collapsible column days, the steering box is basically behind the bumper, and one of the first things that will happen in a crash is that the steering box will be hit, shoving the steering wheel and column into your face or chest (the uncle of my father was killed in his Volvo PV544 in 1967 in exactly that way, and they are unibody so it has nothing to do with separate chassis or not, and ultimately nothing with the discussion I guess). Rear steer cars (like the same era US Fords) weren’t as badly affected, when the crash was severe enough to move the steering box in them you were probably toast in cars from that era anyway.

And, if we put two fullsize US cars against each other (to have something fairly modern passenger car that is BOF to compare with), an early 60s Mopar with unibody for example, and a 2000s Lincoln Town Car that is BOF, I think I would take my chances in the Town Car if I had to have a crash. I am pretty sure that such a late BOF design is better in managing crash energy than an unibody that is 40 years older, type of construction ain’t everything. And then there is loads of other safety advancements during the years…


#20

They didn’t have seatbelts back then, at least in old Chevys.