From Aretha Franklin’s Chain of Fools.

Even Aretha, whom I’ve never seen on a bike, knows that chains do break.
Not often, but they do and then mostly because we abuse them by shifting under power. Protect your chain by shifting to an easier gear before you hit that sudden rise and don’t shift just as you find yourself having to stand and power over that bump in the trail. This means you have to anticipate the right gear before encountering an obstacle that requires a lower gear. It is a good habit to acquire since it will also save you from those stupid low-speed falls when you just can’t get your feet out of the cleats because you’re pushing downwards to power over the obstacle, yet trying to disengage a cleat at the same time.

You’re not as strong as you think

Chains don’t break because you’re so strong, but by extreme sideways bending such as when trying to shift to a lower gear under load. They also break when improperly assembled in the first place. Novices find chain joining quite difficult and often fluff the job – especially if the chain is a Shimano chain. These chains differ from other brands in that they should be joined using a special use-once pin. This pin is so expensive, should you assemble just 100 links using them, you’ll end up with a chain costing as much as a bicycle. Shimano chains require such a special pin because the pins in this company’s chain have more pronounced mushroomed heads, which make reassembly really difficult. The upside is a chain that is much more resistant to sideways forces. The pin is a two-part affair with a tapered head and gentle ramp to ease the mushroom head into the sideplate. Once the pin is driven through the chain, the protruding end is broken off with a pair of pliers.

Fortunately, the punishment for cruelty to chains is light; greasy fingers and frustration, nothing more. A broken chain on the trail or road is seldom catastrophic and is easy to recover from…if you have the right tools on hand.

You gotta break it to fix it

To fix a chain on the ride, or at home for that matter, you’ll need only two tools; a chain breaker and a third hand, actually just a straightened paperclip with a hook at each end that bent to holds the two ends of the broken chain in position whilst you operate on it. Without this tool you’re fighting two chain ends pulled apart by the spring tension of the derailleur and simultaneously operating a two handed tool, the chain breaker. A bit of a misnomer that, since it is designed to fix, not break chains. More accurately, it is a tool that splits a chain and when used in reverse, re-attaches the links.

A chain breaker is one of the essential tools to keep permanently in the bike’s saddle bag. Other essentials are: Alan keys on a multi-tool, tyre levers, a spare tube and patch kit. I also carry a pair of plastic caterer’s gloves to tackle greasy work such as mending chains and, a chain quick link. I keep all this from rattling by stuffing a piece of sponge into the bag before zipping up.

Something else you may want to consider is a quick link. This is a special chain link that snaps together two inner chain links and thus mends a chain using only your hands. However, life is never that simple and when a chain breaks, you’re left with a mangled outer sideplate par that has to be removed before a quick link will work. That’s where the chain breaker comes in once again. When buying a chain link (or Shimano pin, for that matter), make sure it is for your specific chain i.e. for a 7-speed, 9-speed or, 10-speed chain. 7-Speed and 8-Speeds are the same, but all others are narrower and need their own special chain link.

Using a chain tool is pretty obvious

Perhaps the best advice for fixing chains is to practice it at home on a discarded piece of chain until you get it right.