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Last week I started the two-week Pro class at Bike School. I was nervous before it started because I am definitely not a “pro.” And I worried that it would be a bunch of guys with a lot of Shop experience and that the class might move too fast for me. But I am fine and the class is great. Out of a class of 15, there are only two who have worked with any regularity and length in a retail bike shop. The rest have varying levels of experience, but I am definitely not at the bottom. It is a little different from the Intro week, though. Where the Intro week there were five women in a class of thirteen, this class only has two women in fifteen. But the instructors are just as great. And everything we do is discussed and demonstrated first. So, though some of the days are difficult, I’m still having loads of fun and getting my hands greasy!

Last week, I built two bicycle wheels. I’ve heard this called the art of wheel building. But I appreciated that this instructor shared his opinion that it is not exactly an art because a specific procedure must be followed. And though there is a feel to getting the spokes to the correct tension, there is also a tension gauge that indicates when the right tension has been reached.

wheel building

As we talked about the process, it seems like the instructor just glossed over the math of figuring out spoke length. As a former chemistry major, who took a lot of math and math based classes in college, I though this was weird. The instructor pointed out that there are several measurements to take and then there are lots of online calculators already set up that can figure out the needed spoke length for us. Still, though, I was interested in what this secret formula might be. I did not do a very extensive search. But I did almost laugh out loud when I saw this on Wikipedia:

For wheels with crossed spokes (which are the norm), the desired spoke length is

l = \sqrt{ d^2 + {r_1}^2 + {r_2}^2 - 2 \, r_1 r_2 \cos(a)} - r_3


  • d = distance from the center of hub (along the axis) to flange, for example 30 mm,
  • r1 = spoke hole circle radius of the hub, for example 35 mm,
  • r2 = half of effective Rim Diameter (ERD), or the diameter the ends of the spokes make in a built wheel (see ‘Discussion’ attached to this article for explanation) of the rim, for example 301 mm,
  • r3 = radius of spoke holes in the flange, for example 1.1 mm,
  • m = number of spokes to be used for one side of the wheel, for example 36/2=18,
  • k = number of crossings per spoke, for example 3 and
  • a = 360° k/m, for example 360°*3/18 = 60°.

The article goes on, and you can read more here, if you’re interested. For me, I’m satisfied that those online calculators exist. And my wheels came out quite nicely, after about eight hours of work. I also appreciated that the instructor refrained from telling us how much time a bike shop mechanic would take to build a wheel. He said he didn’t want to discourage us. And he emphasized that our next build would go faster. But he also said that an experienced builder could do a basic wheel in maybe thirty or forty-five minutes, and definitely under an hour!

My favorite part was lacing the spokes from the hub to the wheel rim. Getting the tension right was, shall we say, less fun. But in the end, it made a lot of sense. And I think, with practice, I could possibly enjoy the whole process. And the great thing about Revolutions is, there are plenty of wheels with which to practice!

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