Powertap Wheel build

Is this yet another wheel build blog? No, this is my first wheel build. Like said, necessity is mother of inventions. It is very expensive to ship a built wheel to India. I ended up building my first wheel, rear wheel.

Again, I had to wait for Sudhanshu to get me Powertap Pro+, Kinlin XR300 and Sapim CX ray. Yes, it is very expensive to meet him.
Wait, is that all you need to build a wheel?
No.
i)Tools. Truing stand (Litespeed Classic), dishing guage (Parktool WAG-4), spoke wrench (Parktool SW-10) and tension meter (Parktool TM 1).


There are wide range of truing stands in the market starting from insanely expensive to affordable. In case I buy a truing stand, I would go for Park Tool TS-2 with Dial Indicator Guage Set
ii) ReadStudy. The book 'The Bicycle Wheel' by Jobst Brandt, here and here. The book is an excellent one and I recommend it.

Did you miss the spoke holder for holding the bladed spoke?
No, I used pliers wounded with pvc tape.

Is that tension meter necessary?
Good question. If you search the net, you see holy war on whether to use it or not. This made sense to me. So, I used it and recommend it.

Before I get into how I built it, let me explain how I chose my spoke length. It very interesting and simple concept how to calculate the spoke length. The three images below show 1X, 2X and 3x laced wheel. Lacing is the number of a trailing spokes a leading spokes crosses through. However, what you see here is only one flange laced.

To start with, imagine flange and the rim on the same plane.
1X laced Wheel.

2X laced Wheel.

3x laced Wheel.

Yes, you don't see with 90 degree angle at spokes, this is just for example sake.

Consider the bright blue triangle to solve for imaginary spoke length, S'.

R, ERD of the rim.
r, radius of the hub, from center to spoke hole center.
Lc, lacing.
Sc, Spoke holes on flange; Half of total spokes.
θ, Angle subtended.

θ = 360 * Lc / Sc; This should be clear from above pictures.

Now, there are two ways to solve for the spoke length.
The first method (i), using the law of cosines.
s'2 = r2 + R2 - (2 * r * R * cos θ ); I later found this is how the spoke length calculates it.

The second method (ii), using Pythagors theorem
x = r * sin θ; y = r * cos θ
s'2 = x2 + (R - y)2
    = (r * sin θ)2 + (R - (r * cos θ))2;  This is how spocalc calculates it.

Lets now come to reality. Flange and rim don't lay on the same plane, flange is away from the plane of the rim and also they are not equidistant from the center of the hub. For the sake of discussion here, consider one flange. The isometric view of build wheel is something like this. It is not complete view but drawn(not a cad drawing) for what is required.

Use Pythagoras theorem to solve for spoke length, S.

W = Distance from the center of the hub to flange.
s2 = s'2 + W2

Here, it is considered that spoke holes on rim are at the center of the rim. In case you end up with a rim that has offset spoke the effective 'W' is reduced by the offset, i.e."W - S_o",

s2 = s'2 + (W - So)2
Using method (i),
   = r2 + R2 - (2 * r * R * cos θ ) +
    (W - So)2

Using method (ii)
   = (r * sin(360 * La / Sc))2 +
     (R - (r * sin(360 * La / Sc)))2 + 
     (W - So)2

With the spoke length calculated, start with the building wheel. I don't need to copy+paste WWW here. There are numerous articles on how to build a wheel. Every one of them has worked for me. Sheldon Brown's page is where you start and end. Jobst Brandt's book does it step by step with figures. So, go figure out. How I used my bike as truing stand is
+ Stand the bike upside down.
+ With the current wheel keep tighting the brakes untill both rub the wheel. There you got the brakes as a reference to where the new wheel should be centered. Now, remove it and put the new wheel that is to be trued. So, I didn't have to fiddle much with my Parktool WAG-4. A scale/ruler attached with rubber bands to the seatstays served a reference to the radial truing.
+ Complete the build as explained here.

Happy wheel building!!