Do you know why brass has been used for spoke nipples in bicycle wheels for so long?

January 18, 2024

While our bicycles have evolved towards a more technological future, with features like Bluetooth-controlled seat posts and intricately designed non-electronic components, one part seems resistant to change: the spoke nipple.

Many engineers have attempted to revolutionize spoke nipples, yet brass continues to dominate the scene. Even though most brands offer custom-designed spoke nipples, the majority are initially coated with threadlocker to prevent loosening due to vibrations during bike use. The materials used for these spoke nipples are typically aluminum or brass.

For over fifty years, brass has been the primary material for spoke nipples. Brass is a copper alloy, mainly composed of copper and nickel, providing high strength, good plasticity, and resilience to both cold and hot environments. Despite its prevalence in everyday items like doorknobs, trumpets, and sextants, the question remains: why does brass hold its ground in spoke nipples?

Why not use stainless steel, a material widely employed in various bicycle components today? The answer lies in the unique properties of brass. Brass is softer than stainless steel, allowing for more elongation when subjected to loads. "When spokes are in use, they are always under different degrees of tension," explains Scott Boyd, the product manager at Sun Ringle, closely associated with Wheelsmith Spokes.

Moreover, brass serves as a natural lubricant. If both the spokes and the spoke nipples were made of stainless steel, wear and tear could become an issue. Brass's additional flexion provides a slight stabilization of friction when spokes experience unpredictable stress levels.

It's worth noting that Sun Ringle has shifted to low-lead spoke nipples on many wheelsets, especially those for children's bikes, to avoid potential health hazards associated with materials causing cancer, congenital defects, or reproductive system issues.

Brass is indeed softer than stainless steel, but its ability to allow more stretch under load makes it valuable. "Material always undergoes some slight deformation when tightened due to the threads' slight deformation," explains Scott Boyd. The material's response to this deformation is one reason why bolts tend to stay tight. Brass, being malleable, assists in stabilizing friction when spokes are under unpredictable stress.

Additionally, brass and steel, being different materials, can lead to corrosion if not handled properly. The concept of "galvanic corrosion" depends on the anodic index of each material. Brass and steel have a relatively small difference in their anodic indices, making them safe to use together. In contrast, materials like aluminum have a larger difference, making them less suitable as spoke nipple materials when paired with stainless steel spokes.

While discussing stainless steel and aluminum, it's essential to mention titanium alloys. Titanium has a small difference in anodic index compared to stainless steel, making it suitable for spoke nipples. However, the cost of titanium alloys is significantly higher than brass, adding to the overall expense of bicycle wheelsets.

In the realm of high-tech bicycle designs, the laws of physics still apply, even to the bikes we consider the "future." Unless a more suitable material is discovered or someone creates an affordable all-carbon bicycle wheelset, including rims, hubs, spokes, and spoke nipples made from carbon fiber, brass spoke nipples are likely to remain unbeaten.

The sight of technologically advanced designs on our bicycles is undoubtedly refreshing. Yet, until a more fitting material is found or until someone manufactures a not-too-expensive, all-carbon bicycle wheelset, including carbon fiber spoke nipples, brass will continue to hold its place.

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