How to prevent my chain from breaking?

Question

After my chain has broken what should I know about buying and maintaining a new chain (apart from lubing it and replacing when it 'stretches')? Do you keep a spare chain, or a spare link?

I have a commuter bike (a Kona Dr Dew) with Shimano dérailleurs.

The first chain was replaced "worn to at least 100%" after the first 6 months/5000 km. The cassette seems OK and not worn. This was the second chain, replaced two months ago. I noticed occasional slipping gears but don't know whether that was the chain, or the indexing of the gear shifter.

The chain (the replacement chain, which broke) is an SRAM PC-951 which Google says is "our most economical chain".

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Update - it wasn't the removable SRAM link, it was one of the factory links that broke. Because it had been skipping and the previous chain worn more than 100%, I asked to replace the chain and the cassette (even though he agreed that the cassette didn't look really worn, he said 5000 km is too far for a chain); and got a chain stretch measuring tool, if replacing the chain every 6 months isn't often enough. Anyway it's tight again now. The new chain is a more expensive SRAM PC-991 (which cost more than the new SRAM 950 cassette). The original parts I think were all Shimano.

Answer 1

To keep your chain from breaking, keep the derailers properly aligned, ease off of pedaling when you shift, and don't "stomp" on the chain when it's not fully in gear. (Folks who don't go back to the non-indexed days probably never got into the habit of coasting while shifting, but it wouldn't be a bad thing to practice a bit.)

Broken chains are exceedingly rare, and are almost always the result of putting load on the chain when it's not fully in gear. The other likely source of damage is having sprockets that are so badly hooked that the chain gets sucked into a knot.

Update -- 6/14/18

An observation I made this week, working on a bike for Christmas Anonymous:

The bike (a 26" full susp BSO) came in with a mangled chain, a mangled rear wheel (half the spokes were broken), and a broken rear derailer. The chain had actually been twisted 90 degrees at one point (amazing that it didn't break), something I'd never seen before. It seemed like the chain had gotten twisted up in the rear cluster perhaps, after the rear wheel had gotten mucked up. (Perhaps a garage accident -- hard to tell with such things.)

So I found a new rear wheel, a new rear derailer, and a new chain, and put it all together. The rear derailer worked fine, once I got it adjusted (involved some cussing), but then as I tried to get the front derailer to work (blasted twist shifters, plus a cable that was routed so that it collected rainwater) I started having trouble with chain suck on the small front ring. I could see that this chain suck likely caused the chain to knot up and twist, and it was only after that that the garage accident occurred, taking out both wheel and derailer.

Since the chain suck was consistently on two teeth a one point on the small ring, I was able to use a round file to smooth out the teeth and eliminate the problem. I'm guessing the teeth had burrs from when the ring was manufactured, and the bike never got used enough to wear them off.

Answer 2

I've snapped a chain twice.
Once the chain was very heavily worn and it snapped at one of the factory links, the second time it was also heavily worn but it snapped at the Connex Link which I may have re-used (I can't remember if I did or not). Both times I was heavily on the pedals, taking off from the lights, and it is not a pleasant experience.

Based on this I'd recommend
1. Get a chain wear indicator. (Sounds like you have one now) and check the chain regularly and definitely replace it before the chain wears out.
2. Don't re-use master links. Replace them when you replace the chain. Also note that some can be installed the wrong way (The Connex link is like that, make sure it is installed correctly).
3. For chains with a connecting pin, don't break the chain in the same spot twice.
4. Use a proper bicycle chain lubricant. Things like WD-40 can just dry out and prematurely wear your chain.
5. Don't continually break and re-connect the chain. Use a chain scrubber if you want to clean it, rather than breaking the chain too often. Although I've given up on the chain scrubber now, I just wipe the chain down with a rag, lube the chain, then wipe off the excess and ride. Doing this after rain helps keep rust off too.

I carry a compact chain tool and a Connex connecting link, just in case. But I'm more vigilant about checking my chain wear and replacing the chain now, so I shouldn't need it.

Answer 3

Above all else, if you've broken multiple chains in a short period of time, it might be your riding style.

Rarely does a chain break in a straight line, being pulled. The energy is fairly dispersed across the links on the top of the chain while pedaling normally, and even under all out efforts, this is the case. When it is NOT the case is when you are shifting, or using extreme gear combinations like big front big back or little front little back. While shifting, the force exerted is temporarily focused to a few links - especially as the chain moves from one cog to another. In extreme "cross chaining" (extreme gear combinations mentioned above), the force is sometimes unevenly distributed to the links at extreme bending angles left to right, a recipe for snapping chains.

It's a little hard to describe but when an experienced rider shifts under hard effort (hill climbing, sprinting) they will either intentionally or habitually "let up" on the pedals during the shift. This has two effects, the first being lack of snapping chains, the second being more responsive shifting. The best shifting setups, adjusted perfectly, don't shift awesome under load, but letting up a bit always helps.

Answer 4

Before anything else, ensure that you are properly securing the master link as this is the most common point of failure.

You should replace your cassette when you replace the chain. The chain and cassette wear fairly evenly. If one is worn out so is the other, and running a new chain on a worn cassette will wear the chain faster.

If the gears are slipping then the cassette may be worn out and/or the derailer(s) are broken and/or in need of adjustment. The derailer hanger might also be an issue.

The SRAM pc-951 is an extremely common chain and in the dozens I've put on I haven't seen any snap on their own after such a short period. It's probably not quality of the chain, and something in your drivetrain is damaged or in dire need of adjustment.

There are a lot of points of failure in a drivetrain; go to a shop, a good one will take a quick look for free.

Answer 5

All the other answers deal with old, worn chains. I'd like to talk about another angle.

I've only had it happen once, while I was stomping up a really steep hill. It was a brand new 9-speed SRAM chain. It snapped at a link that I took apart and reassembled while installing it; I guess that I didn't put the pin in correctly.

Somebody told me that this kind of mistake is easy to make with the modern narrow chains - the plates are so thin, that there's very little room for error when installing the pin. And for this reason, you should never try to reassemble the links; when installing the chain, just keep removing links until it's the right length.

Answer 6

Right now I am doing the opposite: wearing a chain out until it snaps. This is on a 'beercycle' bike that is kept indoors so rust is not a problem. What I know from the experiment is that, so long as the join link is properly assembled and the chain kept rust free (although not extensively oiled) you can go many thousands of miles past the 'stretch' stage even if the sprockets end up as a 'box of neutrals' (to use an automotive term) with only selected gears actually working.

So, in summary, make sure the link is assembled and the chain is rust-free. Oil really is an optional extra, as half the bikes on the road demonstrate.

Answer 7

I've broken a chain today, and it was only a month old therefore 500 km on it tops. Turns out the brand was particularly cheap, and it let go while grinding up a particularly steep hill. Fortunately I was on the saddle at the time, but I was also clipped in and didn't get on the brake fast enough. A slight speed backwards and I ended up gracefully falling off and sliding down the hill for a couple of metres.

The warning sign I heard a slight click every ~5 pedal revolutions, and in hindsight that was every chain revolution.

The chain side plates were bent apart, but the pin was still there so I squashed it back together and cancelled the rest of my ride, gently rode home via the bike shop for a new one.

On later inspection, the pin was only held on one side and the whole chain was kinked. I should have spotted this doing my precheck or normal maintenance, so I assume it parted on the ride to the hill.

Answer 8

On a recent tour I had a chain break twice. I'm pretty sure it was down to trying to start uphill in the wrong gear with a heavy load; this puts sideways forces on part of the chain which it isn't designed for (the second time, I realised at the point when the pin had popped out of one side but it hadn't yet broken in two).

This was on a three-seater with ~50kg of kids behind me, and the twist shifter wasn't holding gear (ie I had to physically hold the shifter to keep it out of top gear), so if I had to stop suddenly in anything other than the lowest gear I got into trouble.

On the same trip I managed to crawl up a few fairly steep hills without incident as long as I was in the right gear to start with (after getting the shifter replaced!), which tells me that when used properly the chains can take pretty huge loads!

Answer 9

A chain breaks by improper installation..I've never broke a chain. When a chain pin is pressed into place it can catch the chain plate on one side and create a hump at the plate hole..you may find it rides fine for a while only to have the chain break under torque..it was only waiting to happen..that goes for new chains, expensive or cheap..improper installation.

Answer 10

Whatever it is I do I guess. I've never had one break. I don't even worry about stretch. If it's dry, I oil it, but otherwise I leave well enough alone. I don't even bother to clean my chains.