As winter approaches the threat of corrosion looms. Corrosion = oxidation. On steel this makes rust (iron oxide). On aluminum we get aluminum oxide. It's nature's way to break things down to more stable states.
Bicycles exposed to weather can be ruined. With wheels, the corrosion that produces the most grief is on nipples. Corroded nipples break.
Brass vs Aluminum
Brass resists corrosion better than aluminum but it's not a total solution. Brass nipples are nickel plated, a coating that barely suppresses corrosion. Deep anodized aluminum fares better. Brass nipples in damp salty conditions turn gray, then black, and crumble like stale cookies. Corroded aluminum produces a white crust.
Brass nipples can induce galvanic corrosion in an aluminum rim because the copper in brass acts as a cathode against aluminum, corroding it. All you need is moisture to drive the reaction. The choice of materials affects corrosion but moisture is everyone's enemy.
Try Soaking Nipples
Consider soaking them in a lubricant before building so they're fully coated and drain so a film remains. That coating lasts for years. Then lace without touching the oily nipples—use a shuffler and pickup device.
Avoid Pressure Washing
Their pressure can be 10X anything weather-borne. Team mechanics can attest to the destructive potential of washers. Better to use a brush and mild soap on rims and tires, then rinse gently. Relube nipples after any cleaning.
After a wet ride, consider rinsing before letting your bike dry. Rain may seem like freshwater but it's not! Leaves in water makes tannic acid and acid rain is global. Many roads also have salt residues. Rinsing flushes these corrosion agents away and also perspiration and hydration drink residues.
Carbon Issues
Carbon fiber creates galvanic corrosion with both aluminum and brass nipples if there is contact. Carbon rims can be made with a fiberglass layer in the nipple bed to minimize direct contact. Know if the rim you're using is made this way. Some rims should be built with metal washers to insulate nipples. Rim makers should make it clear if washers are needed and what shape is compatible.
Many carbon rims (and deep rims in general) do not have adequate drainage for water inhaled during rain. I've seen desperate mechanics drill holes so rims drain during damp racing. Besides slowing you down, a water filled rim makes a moist atmosphere where damage inside is worse than outside.
Reinforce Nipples
Spokes must go all the way through a nipple, past the slot, to the very end. Even a bit of extension beyond the nipple is OK with most rims. If an aluminum nipple fractures, its saucer shaped head breaks off the nipple body because of an abrupt change in dimension. If a spoke runs through that area the nipple won't fracture. Among race mechanics and high performance wheel builders, it is a cardinal sin to use too-short spokes.
Try a multi-flute chamfering tool (with 90º angle to match the nipple contour). Use only very light hand pressure—this is not countersinking as for flathead screws. Just knock off the sharp edge. If chamfering goes too deep your nipple loses ability to align to the spoke's incoming angle.
Tubeless Solutions
Tubless systems resist flats but are messy. Ammonia in some is fuel for corrosion, but even ammonia-free formulas introduce moisture. Tubeless tires can't function without their wet crud so work hard to manage leaks and spills. Messy tubeless practice is a threat.
Lubricate nipples as a countermeasure.
Even when every precaution is taken, the world is still dangerous for nipples—endurance racing, triathletes with hydration drinks, warm salt water exposure, tropics or swamps with onshore breeze—all are deadly. In these cases, wheels must be regularly rinsed and relubricated. Given some maintenance, they'll survive just fine!
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