Wheelbuilding Measurements etc

I recently re-read Jobst Brandt's book the Bicycle Wheel and it inspired to me make a wheel-related post (as well as hand-build some 36 spoke wheels with Mavic MA2 Rims). So I got on my computer and made some basic wheel building tools.

If you've ever built a wheel, you know that before you can begin, you need to calculate the length of spokes to use. I wrote some MATLAB code that calculates the spoke length you need for a given rim and hub combination. If you have MATLAB, then you can paste the following text into an m-file and run it as a spoke length calculator. Otherwise, if you are a computer nerd, I think that C & C++ are similar enough to MATLAB that you could modify the code to work as such.

%Peter's Spoke Length Calculator
disp('unless otherwise implied, all measurements are to be entered should be in mm, but typing "mm" afterward is not necessary')
disp(' ')
D = input('What is the Effective Rim Diameter? ');
disp(' ')
d = input('What is the Flange Diameter? ');
disp(' ')
WL = input('What is the Left Flange Spacing (Center of Hub to Center of Left Flange) ');
disp(' ')
WR = input('What is the Right Flange Spacing (Center of Hub to Center of Right Flange) ');
disp(' ')
S = input('What is the Flange Hole Diameter? (Usually 2.4mm) ');
disp(' ')
X = input('What is the Cross Pattern? (eg. 1 2 3 4; radial=0) ');
disp(' ')
N = input('How many Spokes? ');
disp(' ')
T = 2*pi*X/(N/2); %Spoke Angle
A = d/2*sin(T); %A = Spoke Position Offset
B = D/2 - d/2*cos(T); %B = Radial Component
C1 = WL; %C1 = Hub "Half Width"
C2 = WR; %C2 = Hub "Half Width"
LL = sqrt(A^2+B^2+C1^2) - S/2; %LL = Left Spoke Length
LR = sqrt(A^2+B^2+C2^2) - S/2; %LR = Right Spoke Length
fprintf('The Left Side Spoke Length Needed is %4.1f mm \n', LL)
fprintf('The Right Side Spoke Length Needed is %4.1f mm', LR)

The program works fine if you know all the measurements, and for most rims and hubs a quick google search will get you all the necessary dimensions if the manufacturer and model of rub and rim are known. But if you can't find the information online, or don't trust the source, then you must measure the rim and hub yourself. So I made a few metrics that show how to measure hubs and rims yourself, supposing you have an accurate set of calipers or a steady hand and a good ruler.


The flange diameter is measured from the center of a spoke hole on one side of the flange to the center of the spoke holes opposite that hole. So pick a hole and measure from the center of it to is opposite. To verify you are doing this accurately you should count 8 spoke holes between the two holes for a 36 hole hub, 7 spoke holes between the two for a 32 hole hub, 6 spoke holes between the two for a 28 hole hub, ... (N/4)-1 spoke holes for an N hole hub. The flange hole diameter is kind of hard to precisely measure so it is usually safe to assume it is 2.4mm.


A dimension that is particularly hard to measure, at least for rear hubs, is the distance from the center of the hub to the center of the left and right flanges. Here is one of many ways of measuring this:
Measure the OLD (over locknut distance -- which is usually 100mm for front hubs, 120mm for rear track hubs, 126mm for old rear road bike hubs, 130mm for modern road bike rear cassette hubs, 135mm for modern mountain bike rear cassette hubs, and can be all sorts of things for tandem & other unusual hubs), then measure distance "a" and distance "b," which is the distance from the end locknut to the center of the hub flange for both left and right sides respectively. The distance WL from the center of the hub to the center of the left flange is (OLD/2)-a and the distance WR from the center of the hub to the center of the right flange is (OLD/2)-b.


Another dimension that is particularly hard to measure is the effective rim diameter. The effective rim diameter is the diameter of the inner wall of the rim where the spoke heads sit. One way of measuring this is to drop a spoke nipple in the rim and measure the distance between the top of the nipple head and the outer rim diameter. I have done this by marking a spoke stuck down the hole into the nipple head then measuring the distance "x" from the end of the spoke to the mark. Subtracting this distance "x" from the outside rim diameter will give you ERD, the effective rim diameter.


Hope these are useful to someone.

Headset Tutorial

Hey, y'all. Thought I'd try my hand at a mechanics tutorial since we haven't had much content to post lately (but hey, if you only posted original content how often would you post?). Heres the first in what may become a series -- how to overhaul a threaded, unsealed headset.









Note: I posted this on a popular online bike forum and asked for some feedback and have a couple things to add.

1. The orientation of the ball bearing cage isn't always necessarily ball-side-down, the ball side should face the bearing race, which is almost always down for the bottom race, but can be either way on the top race.

2. When tightening/adjusting the top nuts of a headset, use two wrenches, one to hold the bottom nut in the correct position, and the other to tighten the top nut.

3. Some people suggested that the amount of cleaning of the ball-bearings was overkill. Indeed, if you regularly maintain your headset, all thats really necessary is a wipe down with a clean rag and some fresh grease. This headset (like a lot of "track" headsets, which have no grime seal on the bottom) was thrashed, so it needed a lot of cleaning.

4. I wrote "biodegradeable, please" about what degreaser to use. I was informed that "bio" degreaser is no longer bio-degradeable after it has grease and grime entrained in it. So I'll take the opportunity to say this, use as little degreaser as possible and dispose of it responsibly. Degreaser should be landfilled or taken to a solvent disposal site, not dumped. Regardless of what jerks on the internet say, I still think citrus degreaser is better for the environment than a solvent like tetrachloroethene.

5. The frame (not mine) in the photos is busted, you can see damage in the paint/tubing where the headtube meets the top tube and down tube. If your bike is damaged in this area, its not too safe to be riding hard, and you should keep a close eye on the damage to make sure it doesn't get worse.\

6. Finally, this Park Tool page has everything you could possibly want to know about threaded headsets.