[Note: this is #13 of a series of 20]
Any task with as many variables and intangibles as wheelbuilding is bound to arouse some superstition. Most of my career in bicycle wheels has been devoted to demystifying the structure and the building process. A demystified process has little place for superstition. And "luck," for all its elusive charm, is rarely the explanation for anything.
When a wheel is quick to build, when the parts assemble with less than usual effort, when trueness seems to take care if itself…a builder feels lucky. "What a fortunate wheel this is!" is familiar to any builder. When I was early in my career, I generally gave credit to the rim. Great spokes, hub, truing stand, or background music surely help. But it always seemed the rim was to blame or credit for the general mood of the construction.
I know many builders who feel the same way. A great rim will build easily. A crummy one is an unwelcome chore. While that's true at the extremes, I've discovered it's rarely true in everyday work. The sooner you figure this out, the better your building.
I might have stayed a victim of the "rim makes the build" mentality were it not for extensive rim measurements I've undertaken on several occasions. Guess what? Modern rims are as straight or straighter than the wheels we aim to build with them. There's no question about this. Better rims benefit from many advances in extrusion and shaping technology. Many brake surfaces are CNC machined after hooping and joining. They've also become straighter to meet demands of automated wheel manufacturers.
My measurements show that unbuilt, aluminum rims are regularly within 1mm of concentric roundness. Diameter (of a 700C rim) is about 632mm, so that roundness is 1/6 of 1%. And the roundness is smooth so only tiny effort is needed to achieve a perfect wheel. The same case for flatness. Modern rims are within a fraction of a millimeter of perfection.
If rims are so incredibly straight to begin with, then why do they take any time to build? Really, it should only be a matter of connecting the spokes to have a perfect wheel. Here lies the key: it's actually our building procedure creating errors and problems, NOT THE RIM.
This means a calm, focused method free of self defeating errors will always result in a lucky (aka "fast") build. Where do these errors come from? I can think of two dependable sources:
Impatience and greed can convince you to take a shortcut. Making too-great corrections, using too much tension too early, pretending you're in greater control than you are, tolerating large distractions when your attention is required. All of these will force little errors and misjudgments into the build. Before the wheel is finished, you'll have to fix them all.
(2) Brain Farts
Sorry, I can't find a clinical description to encompass this idea. Basically, the human brain is prone to making the wrong decision when the data is simple. A common version is a 180° incorrectness. How often has an accident resulted from such a mistake? Obstacle on the left and we turn left. Time to apply the brake but foot hits the accelerator. Meant to tighten the nut but turned it counterclockwise. Thankfully, these are not common but if your focus is not strong, such errors will pollute your build.
No shortcuts or farts for these guys.
I've watched myself and other builders do this regularly. The rim is off to the right but your hands make the opposite correction. If you're using small adjustments, the damage may not be immediately apparent. The only cure to "brain farts" is experience and focus. Don't be distracted, pretend more is at stake. Pretend your wheel truing adjustments are being watched by a thousand students.
As a consequence of these two, shortcuts and brain mistakes, a builder is his own worst enemy. When a wheel is "lucky," the credit lies with you. You didn't make a bunch of mistakes to compound and slow the construction. When it's "unlucky," you can rarely blame the rim. Fast, successful building takes a calm and focused mind. Rim, spokes, and hub are ready to make a perfect wheel. Reminds me of children. Parents don't forge, against odds, healthy adults from their children. Kids are programmed to become responsible adults. Parents can screw it up. Don't get the blame backwards. Work together for a beautiful outcome.
Have you noticed this dynamic in your own building? I'm very curious to hear from you.