Dielectric Grease on Nipples?

July 05, 2023

Many of you builders are busy punching out carbon wheels this Summer. Carbon rims occupy a sweet spot in the market, combining just enough function, style, and price point to create a wave. The Tour is underway (2023) and it seems 100% of the wheels have carbon rims.

As with wheels of the past, carbon rims have their issues with nipple friction and longevity. High on the list is galvanic corrosion, where contact between carbon fiber and aluminum creates an electrical current which accelerates oxidation. Worst case is premature seizure or failure of nipples, a tragic outcome when a wheel can cost more than $1k.

To combat friction and corrosion, builders employ oil and grease at the rim contact. Wouldn't dielectric grease be a better choice? We're trying to reduce electron flow and dielectric grease, used widely in automotive applications, is nonconductive.

This topic is the tip of a berg-sized bunch of considerations. If you want quick conclusions, consider skipping to this post's end.

Nipple-Rim Friction
Difficulty turning tight nipples makes wheel building harder and slower. The extra torque needed is because of friction. Excess friction can lead to abrasion and damage to surfaces and greater vulnerability to galvanic corrosion. Before discussing remedies, let's consider the friction's source.

Most resistance to turning a nipple is from friction with the rim, not from the threads. While it's true that spoke threads can stick, they are not the main source of friction. For example, a completely seized nipple is not hard to turn—the spoke simply winds up until it eventually breaks.

The greatest contributor to nipple friction is the rim contact. Like-material interfaces (aluminum–aluminum, brass–brass, steel–steel) often have the most friction. Standard performance wheels (aluminum nipples and rims) are a worst case.

• Geometry of the nipple–rim contact plays a big role. Rims can have sharp edged holes that cut nipples. Nipples can be the wrong size for the rim hole, for example, too large and making extra contact on the sides of the rim hole. Consider using a deburring tool or a tiny grinder if your rim is ragged. 
• Lubrication is key and it must last well beyond the build. Many greases and oils are tenacious for this purpose. Best if they don't disperse, staining the rim's surface, lifting stickers, or requiring a post build cleanup.
• In mechanical assemblies, washers reduce friction and distribute loads. However, do not load your builds with washers unless you've tested the combinations or have expert advice. Wheels are deceptively simple structures but their rules for reliability are often not obvious.

Thread Friction
To reduce thread friction, use lubricants. And remember that half the benefit comes from resisting corrosion inside the nipple. Nipples swallow water down their bores and corrosion follows. I prefer FIX, which reduces both friction and corrosion. There are other materials and strategies which are effective.

Good fitting spoke wrenches are crucial to avoid nipple damage when friction is high. Have a handful of special wrenches—each application may benefit from a particular size or drive design. While not everyone uses splined nipples, know that they cannot be stripped. The spoke breaks in the threads or at the butt before the nipple sees damage.

If a spoke is seized, try a penetrant, giving it enough time (24hrs) to work. Low viscosity lubes like WD40 or Kroil (in the US) are effective. When it's time to loosen, make sure to grab the spoke with a holder or plier so it won't windup.

Spoke Windup is BAD
Spokes that are twisted, even a small amount, unwind with riding. This can make for peculiar break-in period clicking and creaking and lead to untrueness. Aero spokes that are twisted are downright dumb. It's a wheel builder's prerogative to discover twisted aero spokes and mercilessly ridicule the culprit!

Corrosion
The enemy that cannot be stopped. The goal is to slow it down to a survivable rate. Factors to bear in mind:

• Aluminum nipples corrode more than brass but, for most applications, this can be effectively controlled with some of the strategies above.
• Brass nipples can fail in conditions like tropical ocean exposure. See "Cruiser Bob" at the end.
• Carbon rims cause galvanic corrosion especially with aluminum nipples. This happens when two materials trade electrons vigorously, creating a battery which degrades the oxidizing material which is losing electrons. Strategies include those listed above. Reducing friction reduces abrasion that can damage protective coatings.

Dielectric Grease?
Seems logical to use nonconductive grease to resist galvanic corrosion. In theory, it might work. Considerations:

• Nonconductive grease should not amplify galvanic corrosion. It's used on electrical devices that are exposed to moisture—battery terminals, switches, and connectors like spark plug caps.
• Electron exchange occurs primarily where the materials make direct contact. Dielectric grease has little load capacity so it does not insulate against electron transfer. Conductivity is 100% when dielectric grease is present. 

It may seem contradictory, but nonconductive grease will not stop galvanic corrosion because it does not prevent electrical contact. It only protects from outside moisture.

Dielectric Takeaway
Minimizing galvanic corrosion in carbon wheels is best done the same way we limit corrosion with aluminum wheels:

• Design (optimized nipple seat geometry, high integrity anodizing) goes a long way to prevent abrasion and corrosion.
• Greases and thread compounds applied during building add an important layer of security.
• Dielectric grease has too few advantages for wheels. It's best for electrical connections, not nipples!

Bob Kiger, AKA Cruiser Bob
In 1983, a young videographer began bike rentals down Haleakalā in Maui. While he has since moved on, his early experience maintaining the bikes helped Wheelsmith design nipples! Today, sunrise descents of Haleakalā are massively popular and outfits like Bike Maui continue the tradition. The tours start at the spectacular10,000' summit, Pu'u'ula'ula (Red Hill). The riding descent begins just outside the National Park at 6500' and winds down 28 miles with 32 switchbacks and very steep drop offs—vistas, many ecology zones, perfect pavement, a dream!

So what about Bob and Wheelsmith nipples? Tropical weather + onshore ocean breezes = hyper corrosion. His brass nipples with standard nickel plating would often oxidize black and crumble. Nickel is a substandard protective coating. In answer to this issue, Wheelsmith began using Tin Nickel plating under the trade name "Duristan." Second only to gold for corrosion resistance, it's used extensively in oceanography and medicine.

After 30 years of success, Wheelsmith was shuttered by the current owners, Hayes. Good news, cycling can live with nickel plated brass nipples as long as we use plenty of protective lube before and after cleaning!

For an epic dose of historic Maui, check Bob's beautiful retrospective, Tour da' Maui.

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