chain skips only on small cog
 

I was having trouble shifting to the smallest rear cog (while on the large front chainring) b/c one of the jockey wheels would rub against the dropout.

It would shift to the smallest cog if I were on the smaller front chainring, so the LBS suggested lengthening the chain to reduce tension. It worked, and I can now shift to the smallest rear cog.

but I have a new problem. when I am on the smallest rear cog (and on the large front chain ring, i.e. in top gear), the chain skips. It does not skip on the other cogs.

my guess is that this means the chain is too long? I added only one link, so unfortunately I guess this means I either live with the skipping chain or temporarily having to go to the smaller front chainring in order to shift to the smallest rear cog.

bike is a Xootr Swift folder with Capreo hub and 9-speed cassette + 105 derailleur.

thanks for any tips.

jeez Capreo is only a 9t .. Chain replacement is step 1.
the wear of chain would really soon
transfer wear onto the 3~4 teeth that pulls the hub around ..

Sorry, I forgot to mention it is a brqnd new chain.

Have to be where the bike is to say anything else.. this forum is just text.

If it isn't related to chain or sprocket wear, and I'm assuming it isn't, I suspect that the trim is a bit off. Chain length is not a factor since the lower loop tension is set by the RD cage spring, and doesn't make a difference.

I suspect it's more of a trim issue - check lower limit screw - or possibly the hanger is a bit off plane. You might also use the "B" screw to optimize the pulley/sprocket distance.

Jockey pulley was hitting the dropout. Chain is lengthened. Still skips with new chain. There may still be interference with the dropout and pulley, not enough to keep it out of the gear, but enough to cause skipping. If more B screw tension doesn't help I'd try a spacer to get that dropout away from the gear.

Fixed with a Capreo derailleur
 

Hello world, I've recently been having the same problem as the OP (skipping in the 9 tooth) and after some months of tweaking the company that put together my bike swapped the Tiagra rear shifter for a Capreo one (apparently they've just released a larger-capacity version). Despite being technically over capacity, the derailleur works nicely with my 53-38 up front (9-26 cassette) and has more or less eliminated the skipping. Sure, if I'm massively overheard and really push it into a headwind I can still make it skip, but if I cycle sensibly it's no longer a problem.

See also this thread.

It's not wise to lengthen a chain in order to reach the small-small combo, particularly when running a 9 tooth. That combo engages the fewest teeth of any, increasing wear by a large amount. In addition the high gear should not be used very often at all, certainly not for acceleration. I'm sorry, but it's absurd to be running a 53-9 at all (38 mph at only 80rpm) and certainly pushing any high gear into a headwind indicates questionable judgment. Even a 48-9 is only appropriate at speeds exceeding 35 mph.

The bike in question is a folder with 20" wheels. 53/9 with 20" wheels is slightly lower than 53/12 with 700c wheels. Thus, the gear range is fairly conventional.

Very well, but 53-12 is still a vary tall gear. It also makes riding the small-small an even worse option due to the increased angle on a foldable (shorter chainstay). It may have been helpful if we had known you had a foldable right off the bat.

I had my eyes opened. I assumed the talk of 9 tooth cogs was in jest until I googled it. My thought - another bad idea. Of course, since it is possible and everyone wants to push the boundaries for new/different gear possibilities, good sound engineering with reliability and durability being worthy goals to design to gets tossed out the window. If you look in the industrial world you will not find many chains as skinny as we consider the norm now and gears/cogs have more teeth and are thicker. And, it is common engineering knowledge and practice that a dirty environment requires heavy, more robust4 running gear. (I hope I am reading wrong, but it looks like MTB is leading the way for these 9t cogs. The dirtiest environment there is.)

Now, one factor that allows lighter and thinner bike parts is that longevity is measured in thousands of mile, where numbers like two are considered a lot. (Two thousand miles divided by 18 mph = 111 hours. One to two hundred hours and you replace a part? Only in cycling! Rebuilding a machine in a factory every 3 weeks! Or a locomotive engine? We wouldn't have captains of industry if that were the standard.

Ben - sill riding nothing fancier than a 9-speed 12t cog and loving 1/8" track chains and cogs!