Originally Posted by
twocicle
Barring any real tech info regarding the engineering behind stepping the height of ring teeth, I gave it a shot using as examples the FSA Super Road 53T and 52T, and a middle 39T from a triple. All these had pins and varing tooth heights. So with a fine file in hand I set out to profile (file down the height of) some teeth in the vicinity of where the pins are located.
Result... seems to be working. Shifting up from the granny is a touch less quick, but otherwise the chain is no longer "skating" on the teeth. Will need more time & riding to see how this goes. If this is indeed the solution, then it baffles me why TA does not review the tooth profiling of some other manufacturers.
Nuts. On a ride last night had another case of chain overboard (chain tip-toed over the tips of the teeth and dropped beyond the big ring). I'll do a bit more filing (do the sides per Al1943) but otherwise shopping for a different ring that is profiled more to my liking - and hope that works ok.
BTW, in spite of having the Di2 FD outward movement limited to just enough to not have chain rub, the chain drop seems to occur only when shifting to the big ring while the inner cogs of the cassette are in use. Perhaps a factor of this problem is chain angle of attack when moving to the big ring. Problem does not appear to occur when using the outer half of the cassette.