The new season of Game of Thrones started last night, and, surprise, there's no cars. Not that I was expecting any, of course, because I know that a little bit of magic makes people (even fake ones) stupid, and incapable of building anything like a car. But if they could, what sort of car would the GoT world produce?
This is a tricky question. The technology of the GoT world is pretty stunted, but they do have some fairly limited magic going on, so that can help compensate a bit. Even so, the type of cars they'd be capable of producing isn't going to be anything that's going to give much competition even to a '78 Pinto, but I do think a crude motor-driven vehicle is possible, and there's even a way to do it that is thematically compatible with the fictional world.
The basic level of technology in Westeros and the other lands of the world of A Song of Ice and Fire seems to be roughly at a medieval level in our world. They have decent metallurgy, able to make steel, and able to work it into reasonably complex mechanisms like locks and winches, they have glasswork, simple wheeled animal-drawn vehicles, woodwork, textiles, stonemasonry, and not a hell of a lot more. The only sources of power seen other than animal power are windmills, and I assume water-power exists as well.
I think technically, they could be able to make a crude atmospheric steam engine, and while they could probably get a Cugnot-style vehicle to work, a steam-powered vehicle just doesn't really fit conceptually with the GoT world. At best, it'd just be a transplant from our world, and I'd rather come up with something that feels more, well, native.
And I think there is something. There's an engine type that could utilize two substances unique to that fictitious world, and the way the engine itself works is a sort of direct analogy to the fundamental conflict of the series, one that's alluded to in the series title, A Song of Ice and Fire. That engine is a Stirling engine.
A Stirling engine is a closed-cycle engine that works based on temperature-based expansion and contraction of a trapped gas (like regular air) and essentially turns heat energy into mechanical energy. It's been experimented with for driving cars (including some NASA-tweaked AMCs), but poor power-to-weight ratios and worse money-to-people-giving-a-shit ratios kept the engines from getting any real commercial success. But the Game of Thrones world has two things our world lacks that could make these engines make sense: wildfire and the ice technology of the White Walkers.
These two magical elements are unique to their world and are at two ends of the spectrum: wildfire is an extremely hot-burning substance, sometimes described as "fire made flesh" or something like that. It ignites easily, and burns very hot for a very long period of time. It would make an ideal fuel for keeping the hot cylinder in our Stirling engine nice and toasty.
On the other side, there's the White Walkers (also called the "Others") ability to make things like swords, knives, and probably letter openers and wine tools out of remarkably strong ice. But not just any ice — as G.R.R. Martin himself says,
Ice. But not like regular old ice. The Others can do things with ice that we can't imagine and make substances of it.
So, special ice "substances." The Night Watch is always desperate for money and resources — they could take advantage of their far-North location to send out some poor bastards to harvest some of these ice substances from White Walker-infested areas to bring back for use in Westeros' burgeoning automotive industry. Sure, it'd be dangerous, but mining coal's never been a walk in the park, either, and once decent money came into the picture, I'm sure they'd find a way.
So, with these two diametrically-opposed materials, wildfire and white walker ice, you could make a Stirling engine with extremely divergent temperature extremes for each cylinder, and those temperatures would maintain their difference pretty much regardless of environmental conditions — no more dealing with the vagaries of air-cooling or burning kerosene or whatever. These two materials could really maximize the potential of a Stirling engine.
You'd have to build in some precautions, of course — only a very small amount of each material would be needed, since they're both so potent and potentially dangerous. The White Walker ice-material would probably need to be jacketed in regular ice as an insulator, and then made into a jacket of sorts around the cold cylinder.
For the wildfire, a very well-insulated and protected vessel would be needed, with a series of outlets for jets of flame to heat the hot cylinder evenly. A simple sliding valve system could be used as a throttle of sorts, to vary the intensity of the heat — though I admit, I'm not totally sure if that would affect engine speed. Living in reality, I haven't had a chance to play with wildfire, so I'm not really sure how it reacts to things. To be safe, we'll include a very simple idler gear type of setup to allow for a neutral setting or speed control.
So, there's our engine, one that uses materials unique to the world of GoT and is almost eerily conceptually suited for that world. Could it actually, fictionally, really, not-really be built? I think so.
The basic cylinders, pistons, crankshaft, and linkages for the engine I think are well within the capabilities of the better smiths of that world, and the evidence of some brewing industry suggests that they should be capable of making cylindrical vessels that can hold some pressure. The seals between the pistons and the cylinders I think would be an issue, but let's say they're able to figure that out, too. We're already accepting magic here, so why not?
For the rest of the vehicle, I think things will be need to be kept pretty damn simple, especially if they're going to build these in any quantity. The chassis and body will not be that different that most of their basic farm carts, though adding some simple leaf-spring suspension wouldn't be a bad idea. Steering could be anything as simple as a single pivot point with a fixed axle to something slightly more advanced, like a basic Ackermann steering geometry setup.
I think the Stirling engine would be mounted in the middle, maybe behind the seats and under the rear passenger/load area, and power transmitted to the wheels via belt (they seem really good at making leather belts) to a simple, manual CVT-type transmission. I knew I'd find a place to use that goofy idea. Brakes could be simple lever or spoon-type brakes; they can figure that out on their own.
Essentially, there would just be a simple lever to shove the drive belt back and forth along a cone connected to the rear axle — put it at the big end for low gearing to get started, then gradually move it to the apex to get close to a 1:1 drive ratio. There'd have to be some simple spring-loaded tensioner in there, too, but that shouldn't be too big a deal.
Also, at each end of the cone would be a free-wheeling roller, matching the cone size at each end, to act as a sort of neutral/idler gear. This would allow coasting and parking, a way to de-couple the engine from the drivetrain without shutting it down. Because, honestly, I'm not sure you could shut it down, at least until the wildfire ran out, because I don't think you can easily stop a wildfire fire.
The body on this basic chassis could be specified by the client — either simple, basic farm wagons, more elaborate passenger carriages for the high-borns, or even having a shipwright make a sleek little runabout for the King or some wealthy playboy.
So there you go — now you can stop wondering. I do think it would have been possible, just barely, for self-propelled vehicles to be built and used in the Game of Thrones world. I expect by the 5th season we'll be seeing trans-Westeros rally races and some exciting action over at the Braavosi Speedway.