Spoke Replacement
Broken spokes are a common problem on rear wheels. The back wheel takes most of the rider weight and all the torque of power transfer, plus the rear wheel is dished. So rear spokes break 10 to 1 more than front.
Absent blunt instrument trauma, spokes normally break at the elbow or nipple, and usually only one or a few at a time. Spokes flex, and the breaks are caused by repeated stress. It's like bending a coat hanger back and forth. Eventually the metal fatigues and--pop!
The trick to preventing spoke failure is to reduce spoke flex by keeping spoke tension high and uniform throughout the wheel. Factory built wheels, especially on relatively inexpensive bikes, are not built to high or uniform tension standards. If you have broken spoke problems, rebuild your wheel.
If you know how to true a wheel, replacing a spoke is easy.
Tools needed:
truing stand
spoke wrench that fits your nipples
spoke length measuring tool
tools to remove the cogset
tire levers
pump
spoke prep
The procedure to replace a broken spoke on a rear wheel is:
1. Remove the wheel from the bike and the tire, tube and rim strip from the wheel.
2. Remove the cogset.
3. Remove the broken spoke and the nipple from the spoke.
4. Measure the spoke length and note its gauge, usually 1.8 mm or 2.0 mm, or take them to a shop and let a professional mechanic do it for you.
5. Clean everything you can reach.
6. Study your wheel to come up with a theory why your spoke broke and decide if you need a new components. Is the rim dinged? New rim. Are other spokes dinged? Replace them. Are any nipples rounded? Replace them. Do your spokes have way different tension? Time to rebuild the wheel.
7. Buy new components and needed tools. Be sure the spoke is the right length and gauge and that the nipple is the right gauge. If your spoke wrench does not fit all the sizes, buy a spoke wrench that will fit the new nipple--a Park black spoke wrench 99%+ of the time. Read about nipples for more about tool size, especially the problem that you may now have a wheel that needs 2 different sizes of spoke wrench.
8. Put spoke prep on the spoke threads. Beeswax works great and is cheap at the local hardware store.
9. Lace the new spoke correctly, just like all its brothers and sisters, and thread the nipple on.
10. True the wheel.
11. If your spoke tension varies throughout the wheel, either plan to replace more spokes soon or re-tension the spokes.
12. Replace the cogset, rim strip, tube and tire, and put the wheel back on the bike.
13. If needed, adjust the brakes and rear derailleur.
The procedure to replace a front wheel spoke is the same, except simplified because you don't have to remove the cogset.