Comparison of Chrome vs Stainless Steel Capped Wheel Nuts

Comparison of Chrome vs Stainless Steel Capped Wheel Nuts

Background

There exist two types of commonly used decorative wheel nuts, stainless steel capped and chrome plated. Chrome plated wheel nuts preceded stainless steel capped wheel nuts by many years, the latter invented by MacLean-Fogg Component Solutions as a lower cost option for decorative, exposed wheel nut design. Early success of the stainless steel capped wheel nut encouraged continued use and the consequent three-decade evolution to current robust designs.

Steel wheels were the original application for stainless steel capped wheel nuts. The development of cost efficient aluminum alloy wheels initiated a new trend in OEM wheel styling and required a new wheel nut design, the bulge wheel nut. Consequently, a bulge wheel nut version of the stainless steel capped product was developed. Experience with this new application demonstrated another advantage of stainless steel capped wheel nuts, which was improved torque vs. tension characteristics at assembly. The stainless steel capped wheel nut has become the most widely used OEM decorative wheel nut, with nearly 1 billion sold by MFCS’s Royal Oak, MI division in the last decade. Sales continue to grow, exceeding 220 million per year around the world.

The purpose of this article is to report the results of a series of tests comparing performance aspects of the two types of decorative wheel nuts.

Material and Construction

Chrome plated wheel nuts are typically constructed from two carbon steel components, a threaded nut portion and a small end cap. The cap is welded to the hex end of the nut and this assembly is chrome plated. Due to the nature of racking in the chrome plating process, the threads are not fully covered with plating. The result of this incomplete plating coverage is the introduction of rust in the threads during the plating process.

Stainless steel capped wheel nuts are constructed from two different components, a carbon steel nut and a stainless steel cap. The nut is plated with the customer’s preferred plating and friction modifying topcoat prior to assembly with the cap. The cap serves to cover the entire hex portion of the nut, terminating at the bulge, where the crimp is achieved. Since plating is accomplished prior to assembly with the cap, full plating coverage exists on all surfaces, thus preventing the occurrence of rust in the threads.

Test Schedule

A series of tests were conducted to evaluate the differences in performance that exist between chrome plated wheel nuts and stainless steel capped wheel nuts. They are as follows:

1. Torque vs. Tension

The object of this test is to document torque vs. axial tension characteristics for chrome plated and zinc plated wheel nuts. This test is intended to be relative, revealing differences that exist between two wheel nut types with two stated plating types installed on aluminum, steel and steel inserted aluminum wheels.

2. Torque vs. Tension with Corrosion

The object of this test is to introduce corrosion to the assembly in a manner simulating corrosion during the life of a vehicle and document its effect on torque/ tension data for the two nut plating types.

3. Corrosion vs. Installation Impact

The purpose is to evaluate corrosion on the decorative surfaces of the wheel nuts after multiple installations with an impact driver tool.

Summary

The torque/tension tests show that the stainless steel capped wheel nuts clearly exhibit a distinct advantage over chrome plated wheel nuts in all but one application, that of steel wheels. Chrome plated wheel nuts installed on steel wheels showed marginally better performance. SAE J2316 requirements were met in all of the stainless steel capped wheel nut tests, whereas chrome plated wheel nuts failed in one of the three categories.

Corrosion introduced during torque/tension testing affected both wheel nut types similarly. The lowest clamp load recordings of all the tests were with chrome plated wheel nuts on aluminum wheels. This may be of concern, depending on specific vehicle application. The corrosion/ damage test showed a distinct advantage with stainless steel capped wheel nuts. Though chrome plating does not rust, the carbon steel nut that is covered does. Damage to the plating, typically from wrenching, permits corrosion of the carbon steel to occur. This corrosion is accelerated by time and additional wrenching, continuing to consume the carbon steel under the plating. Stainless steel on the other hand is resistant to corrosion. The corrosion that does occur is significantly less and appears to be limited in nature. In addition, the sacrificial nature of the zinc plating protects the carbon steel nut in the stainless steel capped assembly.

In addition to the assembly and corrosion advantaged of stainless steel capped wheel nuts, the manufacture and use of stainless steel capped wheel nuts presents fewer hazards to the environment than chrome plated wheel nuts. This certainly has no minor impact on the cost of producing chrome plated wheel nuts stainless steel capped wheel nuts are and will continue to be the lower cost decorative wheel nut choice.

Stainless steel capped wheel nuts outperform chrome plated wheel nuts in torque/tension characteristics and corrosion resistance. The unique design of the stainless steel capped wheel nut is durable and exceeds the life of the vehicle.

If you would like additional details regarding the test procedures and results discussed in this article, please contact us.