Hey guys,

Recently replaced my entire drivetrain on my Stumpy HT as it was quite worn from the summer. I replaced the cassette with the exact same model it came with (LX-M580), and the chain I upgraded to a HG-93 from an HG-53. Took me a couple weeks to find a new LX middle chainring, so I was using the older one in the meantime. This combination worked fine.

Anyway, a couple weeks later I tracked down a new LX 32t middle ring (exact same as previously installed) and put that on. But now I'm running into an issue where my chain is dropping to the small chainring sometimes when I use the bigger cogs in the back. This especially happens if I back pedal, or am leaning over some while turning left.

I can't figure out why this is happening though, the FD is in exactly the same position as before, and the middle rings are completely identical except that the older one is pretty worn. The new middle ring is true, and all of the teeth appear to be fine. Side by side with the older one it is completely identical, yet installing the older one fixes this problem. The problem is sporadic, yet as you can imagine seems to happen at the worst times, occasionally leading to chain suck.

This happen when I'm in the any of the 3 biggest cogs, but like I said it doesn't happen every time either. My chain is already a couple links shorter than what most websites recommend to avoid excessive chain slap on the single track, but I know what gearings to avoid due to this so it's not a problem.

Any ideas on what else I can check?