December 17, 2011 5 Comments
[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.
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.
November 02, 2021
You have a point.
Even the differences in spoke hole drillings, especially with extreme aero rims could be registering earlier unless i’m just screwing ahead. as happened to me lately, with a nice combination of wrong-turning.
to be frank, i’m still an bicycle-mechanic-apprentice in my last year (hopefully, tests coming up and i build wheels almost daily now). though i have build wheels before that and they still ride true. but it’s eerie how your thoughts match my latest learning: namely that minuscule lapses of concentration, even with the benefits of routine, can produce loads of extra work. more thinking is the key for me.
as gerd schraner nicely put it: it’s never the equipment. it’s you.
thanks, keep it up.
November 02, 2021
Thanks for continuing to provide a variety of thought provoking posts here Ric—I always learn something of value when I stop by.
That said, I’ll disagree with your estimation that modern rims are never the source of ‘luck’, or the lack thereof in our builds. I’d guess that as many as 10% of the rims that pass through my hands in a year are ‘out’ by a significant amount. Laying them on a flat metal table is enough to see it—no other measuring need be done.
And, having said that, I’ll also agree that more often, we are the cause of our own mistakes or lack of ‘luck’. Distraction or inattentiveness, even for a moment, can add minutes to an otherwise ‘lucky’ build.
November 02, 2021
Nicely explained and written. Pretty much the same thing I’ve experienced over the years. You’re the best, keep up the great blog!
November 02, 2021
You make a great point: the overall size and shape of rims are not the relevant variables in a “lucky” wheel. However, I think that there may be two others.
What about evenly cut spokes? If a spoke has roughly two full thread rotations per millimeter, then a fraction of a millimeter variation in the length of a wheel’s spokes will result in dramatic variations in tension (assuming that each nipple is turned an equal amount of times). Perhaps this is only a practical concern for builders who are cutting their spokes to size, but I noticed that I had far more “lucky” wheels as I became better at cutting spokes.
Secondly, I think that there is an aspect of the rim that has not been ruled out – the drillings. Whether rims have stainless eyelets or noneyeleted, beveled surface, it seems that variations of less than a millimeter here could make a big difference in tension. I do not have evidence beyond the anecdotal, but I would be very interested in seeing the margin of error in nipple hole depth.
Thanks venturing into the have of the mystical.
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Hridayananda dos Santos
November 02, 2021
I have found that my luck has been tremendously improved with the use of the problem solvers nipple driver. Starting the tensioning process knowing that all the spokes are threaded on evenly and then applying layers of tension to the entire wheel consistently, full turns, half turns and quarter turns has surprised me with quite a few voila moments. As I reach the right tension the rim is not so miraculously true radially and laterally. And I sing the song and dance of success while my wheel dances the ballet of the interplay of opposing tensions perfected.