Derailleur adjustment with compact crank

[amartha]

Having just converted a triple to a compact crank on one of my 5 bikes, I have learned a lot.

I needed a 165 mm 9-speed crank for my short legs. The only model available was the Shimano Sora. I liked it -- much lighter than the Truvative triple.

FSA 9-speed compact cranks only come in 170mm lengths which would cause me too much toe overlap with the front wheel.

The compact crank works with a double front derailleur and triple rear derailleur. I replaced a Shimano Tiagra triple front derailleur with a Shimano 105 double front derailleur.

The compact crank must mate with its bottom bracket. I replaced a generic Truvativ triple bottom bracket with a Shimano hollowtech.

The Shimano 105 triple rear derailleur works perfectly!

Depending upon the other components -- 10 speed or 9-speed rear cassettes and shifters, the compact crank doesn't need Ultegra level, especially if the rest of the compenents in the drive train are less than Ultegra-level in quality.

[aicabsolut]

Why are you using a long cage rear derailleur?

[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.