hello, does anyone have any ideas on what is wrong here -
I have recently snapped two chains on my fixie, each time only one side of the link breaks. The bike is a converted 80s road bike, originally I converted the back wheel (re-dish etc) but a few months ago I bought a track wheel and went fixed. The chain looks like it is aligned correctly and runs quiet when not under load but I have a short very steep hill on my way home and whenever I hit this i get some horrible noises from the chain followed by a clunk as a link breaks.
Check that the chain tension is not too tight. Fix any tight spots if possible.
Check that your chain is not worn out and installed correctly
Check your chainline. Even though “it looks” aligned, it’s quite hard to tell unless you measure it.
IMO, it sounds like your chain is too tight. Frames will flex slightly under load (like climbing a hill) and cause your chainline to go off. Keeping you chain slightly slack will prevent the chain from being stretched too much and snap when this happens.
With a ruler or tape measure. Measure how far the chainring is from the centreline of the seat tube. Then measure how far the cog is from the centre of the hub (the centre of the whole hub, not the midpoint between flanges). Both should measure the same or very close.
Re: chain tension
It should be tight enough that it’s not flapping around but loose enough that when you hold the bike up and spin the cranks, they keep spinning. If the cranks grind to a halt or slow down quickly, the chain is too tight.
IMHO, chain tension is not super critical - there’s a reasonably wide range of chain tension that will work fine.
Alignment is my guess also, the dramas only started when I went fixed and a new rear wheel. I suspect my shoddy attempt of adding spacers to centre the wheel was not well done.