Broken Spokes and Wobbly Wheels
Snapping spokes is a thing of the past. I broke about 20 spokes between 1976 and 1982, but none since, because spokes are better now. These days if you break a spoke it's probably because you shifted the chain past the big cog and scarred it badly, and within a month it just gave up.
Wobbing wheels are ever-common. The left- and right-side spokes play tug-o-war with the rim, and as long as the hub has the same number of spokes on each side, and the tension is balanced (no slackers, no ultra musclemen), the wheel will run true. If even one spoke gets loose it'll upset the balance and causes a wobble. Tightening that spoke makes the wheel run true again, and when the rest of the spokes are still tensioned, that's an easy fix.
It's more complicated when a wheel goes wobbly due to an accident, or you've neglected a loose spoke so long that others have worked loose also, and now instead of dealing with one spoke, you may have to deal with (tighten and loosen) four, seven, or eight of them.
If you're a pure wheel rookie, you may do more harm than good, and you surely won't do a pro job, so you'll have to take the wheel into a real wheel pro for fixing. But if the goal is to get the wheel true enough to ride without rubbing on the brake or the frame, you can do that. Here are some tips--
1. Identify all the super loose spokes, and tighten them enough to barely twang. If the wheel still wobbles toward those spokes, tighten it more util it's good enough.
2. If the rim has been damaged, it's trickier. You still tighten loose spokes to pull the rim back, but it takes more tension to pull a bent rim back than a straight one. If you overtension spokes in one area to pull the rim back, you'll create a flat spot (a hop) in the rim there---UNLESS you loosen the spokes on the other side of the hub.
3. A damaged rim that requires uneven spoke tension to run true-ish will always give you trouble. Ride it home and throw it out.
How rim stiffness affects wobble
The lighter the rim, the fewer the spokes, the greater the spoke tension, the more magnificent the wobble. A heavy, wide rim is more likely to be laterally stiff, and a stiff rim isn’t thrown out of whack as much as a light one. When a broken spoke is part of the picture, touring rims do better than light racing rims.
How spoke count affects wobble
The more spokes the less dramatic the wobble when one breaks. And on that note, when the load is shared by more spokes, you’re less likely to break one in the first place. All things equal, the smaller the distance between spokes, the smaller the wobble when a spoke breaks.
How spoke tension affects wobble
The higher the spoke tension, the bigger the wobble when one breaks. On top of that, the fewer the spokes the greater the tension requirements to make a strong wheel. That’s why 20-spoke wheels are a bad idea.
How rim size affects wobble
A smaller rim is laterally stiffer. It’s harder to twist. And for a given number of spokes, the smaller rim has a shorter spoke-to-spoke distance than a larger rim. With the same cross-section, a 32-hole 650B rim is stronger than a 36-hole 700c rim; and an even smaller 26-inch rim is stronger still. That’s not a case for smaller wheels—other consideration trump the difference in wheel strength—but it is a fact nonetheless.
Why do spokes break, and is there anything you can do to prevent it?
They break from fatigue. Fatigue comes from flex. Flex comes from looseness and stress. Most decent spokes break, when they break, at the bend where they go into the hub. A less obvious bend, only now and then but often enough to mention, is where it exits the spoke nipple. Sometimes the nipple doesn’t seat well, and you get a bend there.
Modern steel spokes are about a thousand times better and stronger than the spokes of yore. Modern hollow carbon spokes aren’t good.
Protecting your spokes & wheels
Ride softer tires, which absorb stresses before they reach the spokes. Softer usually means bigger usually means wider rim, and then you have all of these factors in your favor.
Conservative recommendations
Ride the widest rims you can tolerate, with as many spokes as you can stand, and protect the rim with the biggest softest tire your frame will fit.
Last Words on Spoken Brokes
They’re not a big deal, and it’s something every rider should experience at least once. They’re easy to replace; the wheel is easily restored to new-like condition, and off you go again, smoothly.