Failed KMC chain - less than 100km indoor use

Correct, but its just to counter the if you bought off ebay/aliexpress what do you expect comebacks. I don't buy from shops I don't have trust in, just to save a couple of quid.

Hahaha I did! Won't do that again.

And why are we told the brand of chain but not the name of the "reputable" online seller? The implication is that the online seller is beyond reproach, leaving only KMC's reputation in question.

The fault could be with either of them, whilst legally it rest with the seller regardless.

For mine, I simply can't remember, I always keep a spare chain on hand at home,so if I get a problem I can fix it straight away, then order the spare replacement. By the time that new spare gets fitted and then breaks itself, it could be best part of a year later.

Lots of places sell KMC x9 chains, Wiggle/ChainReaction, Merlin, Halfords, Bike Inn, I order from whoever has available stock, so its not always the same retailer.

But it costs around 20quid, Aliexpress sell the "same chains" for around 10quid, I don't buy those.

Always looking for ways to extend chain life, and you certainly get more mileage out of a KMC than I do; what's the advantage of removing then bringing back as opposed to just leaving on until it reaches the second point?

The presumed advantage is that the problems arise when you put a new chain on a worn cassette - so you put worn chains on worn cassettes, and the chain change over is an opportunity to clean the grime encrusted chain at least once during its life. I have followed this system for many years. Four chains seems to be about right for 2 alloy chainrings and a cassette

The idea is the chain wears faster than the cassette and putting a new chain on a part worn cassette doesn't run smoothly and/or wears the new chain rapidly. Take your chain off when it's half worn and fit a new one until that's half worn, then refit the first chain. You could use three or four chains depending on your chain:cassette wear ratio. Worth it? I don't know, I'm not that organised.

The main issue is ensuring you don't run an overworn chain on a cassette - or chain rings. A worn chain puts load on a single tooth and tends to ride up the tooth.

Once the teeth are worn, an unworn chain doesn't mesh properly with the teeth and under load slides up the worn tooth and in extreme cases skips.

The classic wear for a mountain bike is the 11T ring, which with its few teeth to spread wear, and tight radius is both prone to wear and slipping. Many MTB cassettes are ruined by on-road riding where the low gearing for off road tops out and people tend to do a lot of riding in it. I notice quite a few e-bike riders tend to rely on motor torque rather than using the full range of gears, and they will tend to have premature cassette wear.

I get 3 - 4 chains per cassette but don't bother with complicated routines. Simply avoiding excessive wear before changing the chain by checking wear. I've not had to change chain rings yet with that regime.

I know a local cycle mechanic who claims not to worry about chain wear but allows them to wear and then changes the lot but that seems a great way to risk an accident and chain rings aren't cheap.

Cdl888 wrote:

Chain was bought from a reputable online retailer, one of the biggies so would be disappointed if it was fake.

Reputable online retailer, reputable brand of chain. Yet you have already decided where the fault lies - else why name the chain, but protect the retailer's identity. I'd trust KMC above any online retailer. And what about the "dry lube", why is that not in question too?

Quote:

I have since found some forums from a few years back where KMC chains were failing ...

You name it, there are "some forums" about it failing.

My daughter had one go on her MTB the same way, although in that case it was a SRAM chain. I counted 17 cracked links. If I was back in the aerospace biz I would have had it tested to see if the heat treatment on the plates had been missed. 

A friend had something very similar. SRAM chain on a new bike - within a few weeks it had multiple cracked plates... I noticed when I was fixing his chain for the second time on the same ride 
SRAM replaced it under warranty (via the bike manufacturer)

I think multiple links in the chain crack, so get weakened, and when you put a load through the pedals, in my cases its been to pull away from a stop or hitting a steep hill, and Im not generating stupid power I might be rugby player weight Im not rugby player fit, in that split second as the load spreads across the chain the weakest links fail.

this picture gives you some idea, as you can see the link to the left/down of the broken one is showing a hairline crack as well.

and it had only done at most half the mileage Id expect from it given it was basically only dry weather use and was in good nick for wear.

Ive had 3 chains break in 20 years of riding and 2 have been KMC chains within the past 2 years.