The car industry today, worldwide, utilizes aluminum wheels on approximately 60% of all the vehicles manufactured-vs steel wheels, and this percentage grows yearly. Some car manufacturers utilize an almost 90% ratio in aluminum vs. steel wheels. The reason that the car industry has shifted from steel wheels to aluminum wheels is that aluminum wheels are lighter, look better, and therefore, offer better gas mileage with weight savings and better performance and handling.
Most aluminum wheels are CAST one piece wheels. Cast one-piece wheels comprise approximately 80% of the marketplace and are the most common. There are different casting methods and heat treatments available, as well. Finally, the quality of alloys used, from recycled aluminum cans to hi-grade alloys, affect the porosity and hence, the strength and durability of the wheels. These production processes are also the most cost effective, so you will see these as the most common type of aluminum alloy wheels used in the factory production cars (OEM) industry, as well as the aftermarket industry. The quality in the final prep and painting of the wheels naturally affects their appearance, and reflects a certain quality standard in regards to their durability to rust, corrosion, and appearance.
A trend among the hi-end marketplace is that of modular wheels. MODULAR wheels are referred to as multi-piece wheels, and come in 2 piece or 3 piece versions. A 2 piece wheel consists of a barrel, with the face of the wheel affixed, via mounting or assembly bolts to the barrel. A 3 piece wheel, on the other hand, is a bit more complex - consisting of the face of the wheel, an inner and outer rim section which are all bolted together to form one wheel. These wheels are generally substantially more expensive, and offer a very sophisticated, elegant, sporty look. They also have advantages, in that as modular wheels they can be repaired, usually by replacing the damaged portion of the wheel only. rather than replacing the whole wheel. They are generally manufactured with higher tensile alloys, and are therefore stronger and generally lighter than cast wheels. These wheels are generally only available in 17"+ sizes and create a striking addition to any wheel. One point to note, --there are many one piece wheels designed with fake assembly bolts or rivets, to create the appearance of a modular wheel.
A new and growing trend are Forged wheels. Generally speaking, these wheels are lighter and stronger --- but this is not always the case. However, due to their high temperature heat treating, and new rotary forging process, these wheels, generally do have an advantage over cast wheels. However, in light of the high cost of manufacturing, they still comprise less than 10% of the marketplace. Their sales price is also quite high.
The Billet wheel is another method of making wheels. These wheels are "milled" out of solid aluminum, and can be easily hand crafted to any design with today's technologies. They are strong and expensive and can be seen generally on older custom hot rods and some trucks and SUV's.
Magnesium wheels have long been used in the racing industry, especially Formula 1, etc. Magnesium is an extremely light metal; however, it is not recommended for long-term road use, but for hi-end racing. These wheels comprise less than 1% of the marketplace.
The finish is an important factor in the appearance and quality of a wheel. Most wheels today are painted in different shades of silver paint or other colors. Some manufactures clear-coat the wheels for protection and durability. As in alloys, there is a distinct difference in the quality of paints and the type of clear-coat paint that is used.
Some wheels are made in a polished finish. This allows the metal to be polished to its bare metal, removing all the paint and the appearance is quite reflective, almost like chrome. The drawback to polished wheels is that they tend to oxidize very quickly, which reduces their luster and they have to be continually polished and kept up.
Another popular finish on wheels is a chrome finish, which resembles a bright mirror finish. This is accomplished by stripping a wheel to its bare metal and applying different layers of metals, finishing off with a nickel layer, which creates the mirror finish.
Yet another finish is called a machine face cut finish, which is a metal that's polished and clear-coated. It creates a two-toned finish to the normal silver painted finish and is ideal on flat surfaces. Other forms of finishing a wheel are done by various methods, ie: sand blasting, ball-bearings to create a luster, and other forms and different types and colors of paint.
In today's marketplace, most people exchange their existing wheels and tires for larger wheels and tires. Generally they move from 15-16" OEM, factory sizes to 17-20"+ aftermarket sizes. The trend is towards bigger is better, and it's never been more evident than in today's marketplace!