Much talk of rim washers these days. When to use them? Which are best? While seasoned builders have questions beyond this post, for the rest of us, here are some considerations about washers to keep in mind.
Washers are often invoked to prevent galvanic corrosion between nipples and carbon fiber. The materials of nipples (brass and aluminum) wants to exchange electrons with carbon fiber. Direct contact makes it easy for corrosion to occur.
Simply for the purpose of discouraging corrosion, are washers sometimes overkill? Some points on this topic:
90% of carbon rims are built with aluminum nipples. Think, these issues must be controllable or we would not have a functional sport.
Aluminum nipples that fail from corrosion often do not have enough spoke penetration. See here. If the nipple breaks at the saucer head and spoke length was short, don’t blame corrosion.
Nipple anodizing varies hugely. Deep anodizing with integrity is very corrosion resistant. Non-anodized aluminum nipples are a wheel death sentence. Deep, super anodizing is too rare and builders who enjoy this have little to worry about galvanic corrosion.
A nipple that is dipped or coated with a tenacious lubricant remains corrosion resistant for years. Most nipples that disintegrate from corrosion did not have a decent lubricant coating.
Aggressive pressure or solvent washing purges protective lubricants, that must be reapplied. Nipples are vulnerable to over cleaning. Washers won’t protect them from this danger. If you pressure wash, be careful. It can take paint off frames and destroy suspension systems.
Much bad bicycle corrosion is owed to rider perspiration and energy drink spillage that are water soluble and easily rinsed (not wiped) off. Bikes need regular gentle washing after sustained use.
Washers may or may not be compatible with particular rim-nipple interfaces. They can make an already-thick carbon rim even thicker, requiring longer nipples that, in turn, may be weaker and heavier.
A flat washer seems a good fit in a rim’s flat nipple bed but don’t be fooled. Most nipple beds that seem flat are not. The bed bends around the rim, making a flat washer sit on two tiny points which is not so rim friendly.
Tubeless sealants are potential corrosion inducers. Formulas vary. Products that are ammonia-free are more healthy but are remaining ingredients corrosion inducing or corrosion resisting?
Square drive nipples are deformed at the wrench. Even with good wrenches, square drive nipples experience damage. With aluminum nipples, the anodizing is scratched and corrosion has a foothold. With splined drive (for example), anodizing is not bothered. In fact, the wrench can be aluminum—the loads are so distributed and low.
While it might seem that brass is a good choice for washers, friction rules suggest otherwise. Brass is a slippery surface against steel but against aluminum or brass, friction is high. Stainless has low friction against brass or aluminum. This is great choice for nipple washer, a black colored stainless at a great price (for US customers).
It’s best to apply custom solutions to your wheels. Builders who use washers with certain combinations must validate and I defer to their conclusions. Just remember, rim makers do not intend washers unless they are specified. It would break my heart 😞if you used washers on a rim I designed!