Originally Posted by
Nerull
Chains drop when they try to "shift" off the side of the chainring. This always happens where the chain is moving onto the chainring. The RD sits after the chain has already come off the other side of the chainring, and will have nothing to do with chain drop. Even the tension it provides is mostly to keep it on the rear cogs, not the chainrings. You pedaling provides the tension for that. If it's providing no tension at all, some slack might appear between the cogs and chainring when coasting or backpedaling, but that doesn't sound like when your chain is dropping.
I agree. Or, that's how it SEEMS. Bikes are mysterious. They're scientific but their science is only partly known. I'm not exactly sure when my chain derails. Maybe it's from a micro-pause resulting in a tiny wave of chain approaching the crank. Maybe the rear der has some effect on the formation of such chain-waves. Who knows, not me! : ) I will try anything, firstly with what I have on hand. I'll try a couple more rides to see what happens. If it keeps derailing then I will finally throw in the towel and try to find a flat ring that will fit my chain. Whew!