A hubcap, wheel cover or wheel trim is a decorative disk on an automobile wheel that covers at least a central portion of the wheel. Cars with stamped steel wheels often use a full wheel cover that conceals the entire wheel. Cars with alloy wheels or styled steel wheels generally use smaller hubcaps, sometimes called center caps. A wheel cover is also an accessory covering an external rear-mounted spare tire (also known as a spare tire cover) found on some 4x4 vehicles.
Early hubcaps were very small, sometimes merely covering the greased wheel bearing. These snap onto bulges on the wheel, and to change the wheel they are pried off with a tool resembling a very large slotted-tip screwdriver. This differs from the spinners that serve the same purpose for racing cars and those cars with wire wheels, which were designed to be quickly unthreaded by hand. Most hubcaps were once made of chrome-plated steel or stainless steel.
The rest of the wheel was originally of wood or many fitted metal parts. When pressed steel wheels became common by the 1940s, these were often painted the same color as the car body. Hubcaps expanded in size to cover the lug nuts that were used to mount these steel wheels. The next development was, as an option on more expensive cars, a chrome-plated trim ring that clipped onto the outer rim of the wheel, in addition to the center hubcap. Finally came the full wheel cover, which of course covered the entire wheel. By this time, specialty wheels of magnesium or aluminium alloy had come on the market, and wheel covers were a cheap means of imitating the styling of those. Plastic wheel covers (known in the UK as wheel trims) appeared in the 1970s and became mainstream in the 1980s. Plastic has largely replaced steel as the primary material for manufacturing hubcaps/trims, and where steel wheels are still used, the wheels are now generally painted black so the wheel is less visible through cutouts in the wheel trim. On modern automobiles, full-wheel hubcaps are most commonly seen on budget models and base trim levels, while upscale and performance-oriented models have alloy wheels. Modern aluminum alloy wheels generally use small removable center caps, similar in size to the earliest hubcaps.
Often a hubcap will bear the trademark or symbol of the maker of the automobile or the maker of the hubcap. Early hubcaps were often chrome plated, and many had decorative, non-functional spokes. Hubcaps were immortalized in the Art Deco styling of the spire of the Chrysler Building in midtown Manhattan.
Part of the lore of hubcaps is that on bad roads they have a tendency of falling off due to hitting a bump. In the southwest of the U.S., and in Mexico, there were lots of automotive garages whose walls were decorated with all sorts of hubcaps that had fallen off in the vicinity; they were often for sale. This problem persists today in spite of the many different retention systems that have been engineered. Hubcaps generally use either clip-on retention, where some type of spring steel clip (or plastic clip in the case of plastic hubcaps) engages a groove in the wheel, or bolt-on retention, where a threaded fastener retains the hubcap, or a plastic washer attached to the lugnut itself holds the hubcap on. Honda and, to a lesser degree, Hyundai tend to use the latter system. Clip-on hubcaps tend to pop off suddenly when the wheel impacts a pothole or curbstone, while bolt-on hubcaps are more likely to vibrate loose over time, and tend to rattle and squeak. To prevent loss, many owners attach plastic wheel trims to the wheel itself using an electrical zip tie, which are sold in a silver colour for this very purpose. Enterprising manufacturers also sell a small kit consisting of spare zip ties, a pair of cutting pliers and latex gloves to allow a trim thus secured to be removed easily in the event of a puncture.
In the U.S., during the age of custom cars (1950s-early 1960s), decorating one car with the wheel covers from another was common. Two very desirable wheel covers were those of the 1950 Cadillac (called the "Sombrero") and that of the 1953 to 1955 Oldsmobile, which resembled a huge, three-tined spinner. Aftermarket suppliers included the "Mooneyes" brand (named after the firm's founder Dean Moon) hubcaps and wheel covers that were some of the first independently offered for hot rods and custom cars.
Another variant of the wheel cover is that commonly manufactured by the German wheelmaking brand BBS. These are attached on to the wheel first, then bolted on as if the driver/mechanic is bolting the wheel to his car in the manner of changing their wheel. Commonly made from aluminium, they are designed to distribute airflow, therefore generating downforce depending on the shape. Thus, these wheel covers are functional rather than merely decorative. Although they have been used since the 1970s, a carbon fiber variant has found its way into Formula 1 when it was used by Scuderia Ferrari whom BBS supply its wheels to.
A hubcap was used in poor-quality special effects of UFOs in the movie Plan 9 From Outer Space.