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Wheelbuilding: how to make sure the tension in your spokes is right

When you put tension in the wheel and true it, the spokes can get twisted. Instead of the nipple turning on the spoke thread, it can twist the whole spoke. The tension may look correct, but the first time you cycle down a bumpy road on your new shiny wheel, the twisted spoke will unwind as the tensions in the spokes change, and the wheel will immediately drop out of true.

When your wheel is almost fully tensioned, it’s a good idea to go around the wheel and relieve the stress in the spokes. Start at the valve hole, and choose a pair of nearly parallel spokes from the same side of the hub. Squeeze them firmly together. Work around the wheel, first from one side of the wheel, then the other. You may hear the spokes creaking or pinging as you do this. Once you get back round to the valve hole, check the wheel again for side-to-side wobble. You may need to true and then stress-relieve several times. The wheel is ready when you can stress-relieve all the spokes without affecting the truth of the wheel and the tension is similar to that of a functioning wheel. Some people swear by standing on the rim at this point as a final stressrelief procedure. I say don’t do this – it’s excessive and unnecessary.

Freshly built wheels last longest if given two or three trues as they settle in; it’s worth popping the wheel back into the jig after 100 miles to keep it exactly straight.

Spoke-length mathematics

  • Effective rim diameter – this is the distance directly across the rim, measured from the underside of a nipple head to the underside of the opposite nipple head. This is tricky to measure directly, as the underside of the nipple head is inside the rim. Measure the length of a nipple, from under the head to the end; i.e. the total length minus the head. For DT nipples, this measurement is 10mm (3⁄8 inch). Then drop the nipple through the rim and measure the amount that’s exposed. Take one from the other, which gives you the length of nipple inside the rim. Measure across the inside diameter of the rim, between opposite spoke holes, and add twice the concealed nipple length – once for each end. This gives you the effective rim diameter.
  • If you look at the hub from one side, the hub holes make a circle. Measure across this circle for the flange hole circle diameter, from the middle of a hub hole to the middle of the opposite hub hole.
  • The flange width is measured across the hub, from the centre of one flange to the centre of the other.
  • The flange hole diameter is the size of the spoke holes in the hub – usually about 2mm (1⁄8 inch).

Wheelbuilding how to make sure the tension in your spokes is right

Squeeze hard to stress-relieve the spokes

Effective rim diameter …………………………………….D
Flange hole circle diameter ……………………d
Flange width ……………………………………………………………………..W
Flange hole diameter ………………………………………..S
Crossing pattern …………………………………………………………X
Number of spokes …………………………………………………..N

Work out first:
T = 360 x X/(N/2)
A = (d/2) x sin(T)
B = D/2 – ([d/2] x cos[T])a
C = W/2

Spoke length:

Alternatively, to save time, look on the Net.

Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES
See also bike maintenance tips, tricks and techniques “Tightening the spokes”