With the annual Six Gap Century approaching, some of our Georgia road riders are looking for a quick solution for lower gearing. Short of changing to compact or triple cranks, some are opting to put MTB rear derailleurs and cassettes on bikes with standard 39-53 cranks for the extreme climbing of this event.
I have seen a couple of applications using 11-36 or 12-36 cassettes having problems with the chain dropping off the cassette with any backpedaling while in the big/big cross-chaining combination. Granted, this combination should not be used, but things do happen while riding and it would be better if it did not cause the chain to fall off the cog.
On a Shimano application, it was not quite as bad. It took about 3/4 rotation backward with the crank and the chain fell about 3 cogs smaller. On another bike with SRAM components, about 1/4 rotation backward resulted in the chain dropping off the top side of the 36 tooth cog into the spokes. Not good.
I understand that this is an extreme application and outside the spec, but are there things that can be done to minimize these problems?