Originally Posted by
Collin2424
the rear derailleur spring is no longer strong enough to pull the derailleur all the way down to the smallest cog.
Hi, my memory is a bit sketchy but I think Shimana RDs of that era had a
spring tension adjustment dial on the RD's inner link plate's underside.
The dial looks like a flathead screw and it had 3 or 4 preload settings.
Your RX100 RD might have that. If it has it, increasing the tension may
solve your problem.