Failed wheels are good to work on. They require a bit of detective work. In Cowan’s case, I found his wheel with severely munched alloy nipples. This is a fairly common problem with wheels that have suffered galvanic corrosion at the nipple-rim interface and/or have nipples that have been rounded-off by an amateur mechanic. However in this case, the nipples had developed strange cracks at the top of the nipple. A quick observation showed that the spokes where clearly too long and that the nipple threads had passed beyond the threaded section of the spoke and started to dig their way into the spoke creating thread-like marks. In a battle between steel and aluminium, steel will always win, so the nipples had started to weaken and crack from this ‘interference fit’.
After a little bit of maths, I calculated that the correct spoke lengths were 5mm shorter than the drive side spokes that had been laced into the wheel. Who knows how this happened? Correct spoke lengths are the foundation of a well built wheel. This is one of the many reasons why its good to get a hand-built wheel by an experienced wheel builder who you can put a face too. Someone who will be accountable for the quality of their work. A wheel builder can advise on things like whether choosing brass or alloy nipples will work best for you, depending on your type of cycling and maintenance schedule.
With a fresh batch of DT Champion spokes, the wheel was quickly rebuilt and this time with the correct spoke lengths and more durable brass nipples and spoke head washers. Cowan is now off to ride the Cape to Cape multi stage mountain bike race with a rebuilt wheel that should last the distance.
Rim: Bontrager Rhythm Elite TLR Disc 26in (Offset 28 hole)
Hub: Bontrager Elite (28 hole) 142×12 Rear axle
Spokes: DT Champion (Silver), 254mm
Nipples: 12mm DT Swiss Brass silver