Most stock wheels on cars today are either steel painted with a plastic hubcap or a metal wheel with a multistage paint (basecoat of color with clear over the top). Most detailers are familiar with these and know how to deal with them. Chrome and alloy wheels are manufactured much differently.
The major reason motorists buy custom wheels is to enhance the look of their vehicles. When considering a set of wheels, customers weigh their options between chrome, powder coated or polished. But what do these really mean and how should detailers care for them?
Chrome-plated Wheels
There are two types of chrome plating: hard chrome and decorative or nickel chrome. Hard chrome leaves a very hard surface which will resist wear. It is used on automotive items such as bumpers or wheels. Decorative- or nickel-chrome plating is what we typically see on custom wheels today.
After the wheel body is made it is machine finished on what is called a computer numeric control (CNC) machine. If the wheel is to then be chrome plated, it is buffed so the finish has a smooth, high luster which is required for flawless plating.
If the wheel body is alloy, the process involves applying a copper plating base layer that offers additional corrosion resistance. The copper layer is buffed to a high shine, and a layer of nickel plating is then applied to the wheel which provides a bright and reflective layer.
The chrome plating is then applied, which leaves a “bluish” cast to the wheel and serves as a protective “clear coat” to prevent the nickel from tarnishing. This may surprise many detailers who think the chrome layer is what provides the bright finish.
Only one layer of chrome can be applied because additional layers would leave a white, milky appearance on the wheel.
Properly cleaning chrome-plated wheels is easy for detailers, but several cautions should be mentioned. Always apply chemicals to a cool wheel. This is a must if you spray on wheel cleaners that contain acid.
Most manufacturers caution to never use an acidic wheel cleaner on chrome wheels because acid-based cleaners gain strength when heated. Thus, spraying an acid-based wheel cleaner on a hot wheel can discolor or damage a chrome finish.
Once the wheel is properly cleaned, a wax can be applied, but don’t use cleaner waxes or any product with an abrasive in it.
Powder-coated Wheels
Powder coating is done in two ways, either by dipping the item into a fluidized bed of powder or spraying the powder onto an item that has been electrostatically charged. Whichever method is used, the item is then baked to approximately 320-410 degrees Fahrenheit which melts the powder and creates the durable coating.
Once dry and cured, this method leaves a surface that is durable and resistant to chipping, peeling or cracking and the road conditions wheels are exposed to.
There are many types of powders used by wheel manufacturers, some of which are proprietary. To obtain a proper powder coating, the wheel body must be thoroughly cleaned. To make sure the wheel surface is free from any oils, greases or other contaminants, wheels are often rinsed in a weak alkali detergent solution and then etched with acid to remove any heavy oxides.
If a wheel manufacturer uses the spray method of powder coating, it is done with an electrostatic spray gun. Because the powder particles are electrostatically charged, the powder wraps around the wheel, providing complete coverage. The powder remains on the wheel as long as the electrostatic charge is maintained.
Powder coating wheels is an effective way to protect the base wheel material and also add or enhance color as some powders are available in a wide variety of colors.
Cleaning a powder-coated wheel also is easy. Wash a cool wheel with a mild shampoo, preferably with a low pH. Stay away from acid cleaners. If the wheels have asphalt or heavy grease on them, you can use a tar-and-grease remover, being sure to rinse with clean fresh water.
A quality powder coating is very durable, but detailers should apply the same cleaning methods recommended for chrome-plated wheels to be safe. Never apply cleaners or waxes when the wheel is hot. Never use abrasive cleaners or polishes on a powder-coated wheel.
Other Options
A number of wheel manufacturers also offer alloy wheels that are powder coated and/or finished with a machined/polished surface that may or may not be finished with a clear powder coat.
For example, Ultra Wheel offers “Ultra Finish,” which is obtained by machining the surface with a CNC diamond bit that operates at very high speeds to achieve a high shine without the need to plate or clear. Typically done on alloy wheels, this diamond-bit finishing can be used on only specific wheel designs where flat surfaces are present.
Another “bare” alloy surface is Alcoa’s line of forged alloy wheels. These are made from a dense 6061 alloy (an aerospace grade) that is heated to a working temperature and forged to shape. The forging is then CNC machined to its final dimensions and shape, followed by surface polishing.
Alcoa also offers a few select wheel models that feature a powder clear coat.
Keith Duplessie is technical services manager for Portland, Ore.-based Detail Plus Car Appearance Systems , in charge of all installations, training and technical services. He also serves on the board of directors for the International Detailing Association . Keith can be reached at keith@detailplus.com .