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
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.
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
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.