Spokes don’t break as much as they did in the ‘70s and earlier, because spokes got much better in the ‘80s, and spoke failures plummeted instantly. But not all spokes are good and not all wheels are well-built, and spokes still break. I haven’t broken one in 20 years, but I’ve broken more than 20, and I still see & hear about snappin’ spokes.
You have to know what’s going on in the wheel. 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. One loose slacker or broken spoke upsets the balance and causes a wobble. On the road, you can fix the wobble by loosening a couple of spokes on one side and tightening some on the other in the area of the wobble, but who carries a spoke wrench? And if you aren’t a semi-maestro with the spoke wrench, you’ll surely do more harm than good. So you can’t just pack a wrench and think you’re good to go.
A wobbly wheel can shake the bike, and if the wobble is huge, you won’t be able to ride the wheel. On top of that, one broken spoke leads to more spoke breakages, unless you fix it. A wobbly wheel causes jerky braking. (That may seem to be an argument for disc brakes, but it is not. Disc brakes have their drawbacks, too.)
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.
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.