Derailleur adjustment with compact crank

[Cataboo]

maybe 'cause she had it from the triple that she was converting to a double?

[HillSlugger]

My FD has been well behaved on my last two rides but yesterday the RD decided that it wanted to skip past one of the cogs towards the middle of the set. Everything else seemed OK. What would cause this all of a sudden and what do I do to fix it?

[aicabsolut]

Did it do it repeatedly?

Sometimes, we just get the "throw" wrong of the lever. Other than excessive wear to the cassette or chain, that's a fairly good guess when you have skipping problems on one cog and towards the middle. Did it matter which side you were shifting from? (Did it skip only when shifting easier or harder into that cog?)

[HillSlugger]

Did it do it repeatedly?

Sometimes, we just get the "throw" wrong of the lever. Other than excessive wear to the cassette or chain, that's a fairly good guess when you have skipping problems on one cog and towards the middle. Did it matter which side you were shifting from? (Did it skip only when shifting easier or harder into that cog?)

Yes, repeatedly. Yes, in both directions. The chain, cogs, and cranks are all new, with less than 250 miles on them.

[aicabsolut]

Only in the middle on one cog? You might want to check that the cassette is still on there tightly.

Hmm... the only time I had a similar experience it turned out (weirdly) that the rear cable was installed too tightly. I thought maybe tightening it would help because it was pretty new, so when that didn't work, I loosened it and the problem was solved. I'm not sure that's typical, though.

[HillSlugger]

Yeesh, I just realized that I rode this week on my race wheels, the first time in a while. I guess the cogs aren't lining up quite the same as the other wheel?

[aicabsolut]

Yeah, the spacing can be different between wheels meaning you might need some derailleur adjustments to make shifting optimal when switching. Are you running the same cassette spread on the two sets? That's another factor, though mostly has to do with the B-screw.