Derailleur adjustment with compact crank

[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.

[HillSlugger]

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.

Yes, same cassette on both (12-27). Didn't have this problem on my road bike with the triple/long rear cage.

I have discovered that my chain length *will* allow me to get onto the big-big combination. At the other extreme on the small-small (or next to smallest cog) the jockey wheels start to rub on each other.

I suppose I'd be much better off if I could HTFU and learn to ride a 12-25!

btw I made some adjustments to the tension using the barrel adjuster and the shifting was better behaved today, but not perfect. Instead of skipping past the 3rd cog (or was it 4th?) it was reluctant to get up onto it, but only when I was in the small chain ring. I suppose I should be switching to the large chain ring instead of going to this combo.

[aicabsolut]

Whether you have to make adjustments when switching between wheels seems to be bike geometry and individual derailleur dependent...so I'm not surprised you were ok switching with the triple but are now having problems.

When you say "get up into it" are you shifting harder or easier? If harder (which is what I'm thinking when you say you shouldn't be using that combo in the small ring), then loosen the cable by turning the barrel clockwise and see how that goes. The cable tension isn't as finicky as the limit screws so you can play with it more. Or you can start from scratch and loosen it a lot then start to re-tighten until it shifts properly.

If you're only having problems when in the small ring, then it probably isn't your limit screw on the RD. More likely a cable tension thing.

What do you mean that the jockey wheels start to rub on each other? Do you mean the chain is rubbing on the underside of the derailleur cage? That's not a big problem. That's what that part of the cage over the bottom pulley is for. Plus, you've got a fair amount of slack on the underside of the chain a lot of the time when in harder gears. It'd be worse for your derailleur and shifting if the pulleys/cage were rubbing on the large cog when in the small ring / big cog combo.