A broken spoke is annoying, but not terribly hard to fix. Here's how.
Spokes beak for three main reasons: a manufacturing fault, damage, or metal fatigue. In the latter two cases, the spoke usually breaks at the the bend just before the spoke passes through the hub flange. A fatigued spoke will snap right on the bend. A damaged spoke has usually been damaged by the chain over-shifting off the largest sprocket and will fail near the bend, with obvious gouges where the chain has dug in.
A faulty spoke might break anywhere. If an otherwise undamaged spoke has snapped at the thread or in the straight section between rim and hub, it was probably faulty.
A faulty or damaged spoke should simply be replaced. In a properly built wheel, stainless steel spokes don't fail through fatigue, so a fatigue failure can be the first of many. Two or more fatigue failures means the best option is to rebuild the whole wheel with new spokes.
• Replacement spoke
• Spoke key
• Zip ties
1. Remove the wheel from the bike, then remove the tyre, tube and rim tape, unless your rims are tubeless models with fully sealed rim bed, with no access to nipples from behind. Unscrew the threaded end of the broken spoke from the nipple.
Inspect the nipple flats for wear. If they're tatty, now is a good time to replace it. This one looks to be in good shape, so it can stay. Poke the other broken end out of the hub flange.
2. This particular spoke broke in the most usual spot, the rear drive side. These spokes are carrying most of the drive forces and can also be damaged by an over-shifted chain.
Remove the cassette to access the spoke hole in the flange. Here we're unpicking the spoke from the ones it crosses from hub to rim, noting whether it passes over or under the others. On a traditional three cross lacing pattern, a spoke would go under, under, over the three other spokes on its way to the rim.
3. You'll need to buy a suitable replacement spoke. Spokes come in different lengths, depending on the hub and rim you're lacing together; they're available in 2mm length incrememts. The right length is important; too short and the spoke won't pass into the rim bed for support, leaving the nipple carrying the torque loads. Too long and the nipple will bottom out on the unthreaded spoke shaft, or the end of the threaded portion could (on low profile rims) poke through the rim tape, causing puncture risk. On-line spoke length calculators are a great way to find out what spoke length you need. Ours is a perfect match.
4. Getting the spoke into the hub flange can be a task, especially on rear drive sides, where spoke length is short and hub shell width is narrow. Navigating a disc rotor doesn't help, though you should be able to do it without removing the rotor. Don't be afraid to flex the spoke to get it lined up with the flange spoke hole, you'll need to present the very end perpendicular to the flange otherwise the spoke threads will catch. Make sure you enter the hub flange from the correct side.
5. Sometimes the new spoke head won't want to seat squarely straight away, the spoke can take a bit of jiggling and flexing to get it orientated so it points in the right direction and the head sits flat against the the hub flange. Make sure when you thread the spoke that it follows its assigned pattern. Here it's a three cross pattern, so our new spoke passes over two spokes and under the third (not in shot) before engaging the nipple.
6. The new spoke will overlap the end of the nipple, so you'll need to flex the spoke a bit to get it to line up with the open end of the nipple.
If you've removed the rim tape, it is possible for the nipple to get pushed inside the rim and rattle about. It'll usually fall out with a gentle shake. Use the threaded end of your broken spoke to hold it in position while the new spoke is engaged. Once a turn of thread is achieved, the old spoke can be discarded.
7. With the end of the spoke engaged, tighten the spoke with the appropriate size spoke key. Use a dedicated spoke key, not one in a multi-tool as they're often poorly finished and can lead to damaged nipples. We like Park Tool's keys and the Spokey; the Park Tool one is in shot here.
8. Once the new spoke is in position, you can either finish the truing job with a wheel truing stand, or if you don't have one, you can improvise, as we've done here.
Place the wheel back in the frame. Position two small zip ties, one on each seat stay or fork leg (depending on which wheel you're working on) at rim level and angle the ends so they just clear the extremes of any run out. The zip tie ends act as visual guides to the tension adjustments you make as you return the wheel to true.
Replace your cassette, if you've had to remove it. Then when you're happy with the true of the wheel, replace the tape, tube and tyre.