Ever since racers discovered the quarter-turn fasteners invented by William Dzus and often used in aircraft panels, rodders who wanted convenience in attaching hood sides and other panels on their hot rods fell in love with them. They were cool and had that no-nonsense, go-fast connotation. Likewise, when attending dry lakes and Bonneville meets, guys with street rides were equally captivated with the spun-aluminum wheel covers produced by the late Dean Moon starting around 1950. Ever since, Moon discs have been a very popular choice of wheel treatment for rods with a traditional style. The racer look is achieved at considerably less expense than a set of four magnesium Halibrands.
Moon discs (there are other companies making aluminum disc wheel covers, but Moons are the defacto standard) appeal to a surprisingly wide audience. When you park somewhere, the number of people who comment on the Moons, especially people outside the hot rod community, will far outweigh the interest generated by billet wheels that cost 10 times more than those classic aluminum circles with the "sun ray" finish.
So what's the problem with Moon discs? It's a question of aesthetics in mounting them. Whether we're building a low-dollar traditional rod or a high-ender, most of us rodders feel bound by certain accepted fashion principles, written down a thousand years ago on two finned-aluminum tablets found in the desert around Muroc Dry Lake. With Moon discs, it's considered bad form to punch a hole in the discs for the tire valve stems to stick through; it interrupts the flow of the swirling finish. We must mention that Mooneyes still makes Moon discs with a ring of "snap on" clips on the back, and they offer a clean look when installed, but taking them on and off to check your tires will eventually chip paint from your rims. This style is available in diameters from 12 inches and up.
So what do you do about checking your tire pressure? You attach the disc to your steel wheels with screws around the edges, but every time you check your tire pressure, you have to remove the screws from all four of your Moons, lay the Moons down carefully where they won't get scratched, then put all the screws back in when you're through checking the air in the skins. If you're like most of us, where you placed the screws on your disc may vary slightly from wheel to wheel and you have to mark your discs (left-front, right-rear, etc.) and also make orientation marks so each disc lines up with the right spot on its designated wheel.