On Powercranks!!

At last took a plunge into Powercranks! How is I got them is not a happy story. These are very expensive ~$900 for the basic ones. So, I bought them off ebay. The seller had ISIS BB along with it. I always trusted ebay sellers and had not had any problem till now. This time I learnt a $ lesson. My friend was visiting me, so I got them shipped to him. When I got it in my hands I found the BB was bent. :( I don't mean to complain with ebay in general but my first bitter experience.

Obviously, my search for the ISIS BB started. I was bewildered with the rant I found on net. It seems this open standard, ISIS, was created because of the patented octalink BB by Shimano. I hardly came across anyone who had good experience with any brand but SKF. The roller bearings on drive side and ball bearings on the non drive side really got me interested. Alas, it didn't last long. I could not find any online retailer but Vintage Bicycle Press with stock, but they were also vacation. With all the warnings I read on net, I still went ahead and brought FSA Mega Pro.

I really wanted to post video of how installed BB and the PC but I could not get a good video. I need a tripod for my camera, so forget.

It has been just two days I installed them on my bike. My experiences are not different from here (search for powercranks). I could not keep up them in place and rhythm, even for a minute. It was very disappointing. I tried being hero for 5 minutes, lived up to self. Then came the ego hurter, I could not lift my legs to get down the bike. I enjoyed the pain in muscles next day. :) I plan to slowly increase my time on them.



Now that I have every thing I need for my training, I plan to start training soon. I plan to put them here. It will go this way; base period, build period. I don't intend to race, but I want to see what my potential is!

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!!