A kind of four-wheeled motorcycle powered by compressed air, with or without an onboard compressor to top up its tank.
A racing league now exists, with three colour schemes: red-and-brass, like Hope's machine (adopted by the Gold class, among whom Sturdy of West Longleaf and his son are prominent); green-and-chrome, like Briar's machine (adopted by the Silver class, such as Fair Tanner); and blue-and-copper (adopted by the Copper class, notably the Workers' Co-op Association).
There are three prizes for each race: the machine which is ahead when the first of them runs out of air, the machine which runs out last, and the machine that goes furthest.
Other early adopters of the airhorse are the Carters' Guild (represented by Berry Carter and Reliable Carter at the investors' meeting); Cheerfulness Stabler, who runs the largest livery stable in Gulfport (forthright, florid and heavily built, wears tan Victory suits).
Rosie Printer was also present at the investors' meeting, where she asked a question about power loss from using compressed air instead of employing steam power directly.