John, who rode his Dunlop tire. O'er the head of sweet Maria, When she writhed in frightful pain, Had to blow it out again.
Ruthless Rhymes Harry Graham
Tires are the donut-shaped things that fit around wheels to provide extra traction. They also absorb shock and protect the wheels.
Tires on Wagon Wheels
Old wagon wheels had metal tires, made of iron or steel. The metal was put on hot by a Wagonwright. It was then quenched in water, which would make the metal contract tight around the wheel. This gave a lot of strength and durability that a purely wooden wheel would lack.
Modern Pneumatic Tires
Modern tires are pneumatic (filled with air). This provides additional absorption of shock, and helps keep the tire in contact with the ground at all times, for a significant boost to traction.
Prior to World War Two, vulcanized rubber tires were made by adding sulfur to a resin extract from the rubber tree. During WWII, most of the world's rubber trees were under Japanese control, so both the Unites States and Germany put funds towards inventing a synthetic version. Ever since, most vulcanized rubber has been made from sulfur and butadeine, a highly explosive, carcinogenic compound refined from crude oil.
In some cases - especially for military applications - it is preferrable to have tires which are not (as) vulnerable to puncture and deflation as traditional pneumatic versions. There are a variety of ways of acheiving this, but a common method is to fill the volume of the tire with a dense sythetic foam. This provides some of the same rigid-but-compressible nature as compressed air but, being essentially a solid, won't leak out of any holes (indeed these sorts of tyres can keep functioning with sizable chunks missing). Of course, such tires are noticably more expensive, heavier and often have poorer handling characteristics, especially in terms of vibration and road noise.
Early, pre-pneumatic tyres were also frequently stuffed with a variety of substances including sand, junk rubber and horse-hair. Solid rubber tyres were also common (and in a few cases appeared pre-vulcanisation, and even on non-motor vehicles). These were something of a compromise between solid wheels and modern tires - some improvement in the ride and reduction in noise, but at added cost and additional fragility.
One of the neat things about vulcanized rubber is that it melds together into giant molecular chains. Each car tire is actually a single enormous molecule. Unlike metal that you can just beat into a new shape, the tire's shape is set for life. The downside of this is that nothing in nature currently knows how to digest such a huge uber-molecule. Ultraviolet light and ozone can degrade tires, but newer tires have been laced with chemicals to prevent that. Until something new evolves to eat them, tires will live forever. In the US, we throw away an average of one tire per citizen per year.
Game and Story Use
- A thrown or damaged tire can slow down a vehicle. Damaged tires mean less traction, making it unstable and hard to drive. It can also put undue pressure on the wheels, axle or other parts of the car.
- In a campaign set in the 19th Century, wagons and early automobiles might have metal or pneumatic tires. The former provides greater durability, but the later should result in better handling and faster speeds. Depending on how abstract the vehicle and chase rules are, this might matter.
- Considerable variation should occur - quality control was patchy in early tyres and many of them were distinctly under-engineered and prone to puncture or outright disintegration at awkward moments.
- A time traveler from an alternate future where the Axis won travels back to the US during WW2 to give the beleaguered allies the formula to synthetic rubber.
- In the future, the world is cluttered with trillions of discarded tires. A Mad Scientist with an ecological agenda unleashes a tire-eating nanite to solve the problem. Of course, things go wrong, and all the world's tires are consumed, including those on moving cars, those used in the walls of earthships, tire swings, etc.
- After The End, if mutant equivalents of fantasy monsters exist, one might be a rubber-eater.
- Used tires have a variety of civil and military engineering functions, whether as erosion protection for river banks, raised plant containers or makeshift gabions.
- Used tires buried in landfill have a tendency to work their way to the surface over the years - in an after-the-end setting, a partially buried tire might be a useful sign of a pre-apocalypse landfill that can be mined for useful materials.