The reflective, mirrored finish of chrome makes it a popular decorative metal, particularly in the auto industry. However, this decorative finish is also susceptible to staining by magnesium chloride, particularly in the winter. The rock salt that is used to de-ice roads is the most common culprit for causing magnesium chloride stains on chrome. Luckily, since magnesium chloride is an easily soluble compound, getting rid of these stains is relatively simple.
Determine first that the wheels actually are made of chrome metal, rather than well-polished aluminum, to help ensure that the stain-removal methods you use do not damage the metal surface.
Scrub the stain away using cold, soapy water and a soft, nylon-bristled brush, using firm, circular strokes. It is far more effective to use cold water than hot water, because magnesium chloride is most soluble at a low temperature. Rinse off the chrome with cold water, and dry it using a soft, lint-free cloth. Use another soft cloth to buff it to a shine.
Pour a solution of one part white distilled vinegar and one part cold water into a spray bottle. Spray a generous amount of the diluted vinegar onto the stained chrome and let it sit for five to 10 minutes. This allows the magnesium chloride to be absorbed and dissolve in the solution. Blot the chrome dry using a lint-free cloth.
Mix 1/2 cup each of flour, salt and white vinegar to form a paste. Use this to clean more stubborn magnesium chloride stains. Gently rub the paste onto the chrome surface, and then leave it on for at least one hour. Use a soft bristled brush, such as a toothbrush, to clean up the paste, and wipe the surface clean with a dry cloth.
Use a poultice of oxalic acid to get rid of the magnesium chloride. Dampen a gauze pad with some oxalic acid and blot it onto the stained chrome surface. The acid gets rid of the stain by neutralizing the pH of the magnesium chloride, which is highly alkaline. Rinse off the acid with cold water, and dry it using a soft, lint-free cloth.