Chain jump woes

[Skb]

I have a nine speed quick neo. With a new chain and cassette installed by a bike mechanic. My chronic problem is chain jump under torque in ninth gear. Its mostly infrequent but irritating. Perhaps every quarter mile the chain will jump once. I’ve tweeked the high screw and barrel adjustments to no avail. On my stand it shifts back and forth just fine, but on the road it jumps. I don’t want to take it back to the shop and lose ten days waiting.

 

[J.R.]

I have a nine speed quick neo. With a new chain and cassette installed by a bike mechanic. My chronic problem is chain jump under torque in ninth gear. Its mostly infrequent but irritating. Perhaps every quarter mile the chain will jump once. I’ve tweeked the high screw and barrel adjustments to no avail. On my stand it shifts back and forth just fine, but on the road it jumps. I don’t want to take it back to the shop and lose ten days waiting.

Try the B screw adjustment. You might have too much or too little tension and or gap. It's the most neglected adjustment by all of us. When the bike is on stand it doesn't get the same torque as under load. The high and low could be spot on and smooth, but the B screw poorly adjusted will only show up while riding.

 

[Skb]

I assumed wrapping the chain further around the cog would stop the jumping. I’ll tweak it the other way incrementally to see if there is any improvement