Originally Posted by
Pop N Wood
Teach her how to shift and she will stop breaking things.
In spite of weighing under 150 pounds, shifting correctly, and not splitting my chains for cleaning I occasionally broke them until I moved on to 10 cogs with flush riveted chains that had pinned over ends. It's a natural consequence of wear on traditionally riveted chains.
Unfortunately you're only guaranteed strong chains with a 9+ cog bike (10 with Campagnolo) that comes from a bike shop.
Per Wikipedia
https://en.wikipedia.org/wiki/Roller...cle_chain_wear
The lightweight chain of a bicycle with
derailleur gears can snap (or rather, come apart at the side-plates, since it is normal for the "riveting" to fail first) because the pins inside are not cylindrical, they are barrel-shaped. Contact between the pin and the bushing is not the regular line, but a point which allows the chain's pins to work its way through the bushing, and finally the roller, ultimately causing the chain to snap. This form of construction is necessary because the gear-changing action of this form of transmission requires the chain to both bend sideways and to twist, but this can occur with the flexibility of such a narrow chain and relatively large free lengths on a bicycle.
Mushroomed pin ends hold them in place on contemporary bike shop chains so that doesn't happen.
You also need bike shop quality to prevent the broken rear axles which go with freewheels instead of freehubs using the Shimano design or oversize axles with smaller ends.