Sorry for the confusion. This is not from cross-chaining. The chain comes off when I'm on the outer (larger) crankgear, and am on the outer two (two smallest) cassette gears. That is, the chain comes off the crankgear, when I back-pedal.

Yes, I've read the older threads about "If this hurts..., don't do it." But on long rides I do back pedal a few times to help loosen up, and to drop my heel down to stretch my calve muscles.

I also thought more about my post in the middle of the night, and relaized that I got one part bassackwards. The alignment of the outer crankgear intersects the 4th outermost cassette gear. Therefore by not intersecting the 5/6 gear, I'm already biased in a manner that should prevent the chain from coming off, when I back pedal.

I checked some SRAM literature, and saw that for some of their cranksets the chain compatibility is Shimano or SRAM, but for others it states SRAM only. I thought a 10-spd chain is the same? Could the SRAM chain have more "alignment" flexibility than the Shimano?

Thanks again JiveTurkey and others,

Terry