I just replaced chain and cassette on my commuting bike, and the chain skips on the gear that I use most (and on none of the others). Maybe something that will go away as it wears in? More likely a quality control issue with the cassette.

The new chain is SRAM 7/8-speed and the cassette is SunRace 12-28 7-speed.

Please clarify whether this is a power skip or a trim skip, (my terms). Meaning does it skip when you apply more power, or does it randomly skip, as if it wants to initiate a shift.

Mild power skipping is caused by unmatched pitches, or small burrs on a sprocket and tends to improve with breaking. Trim skipping is caused by things like poor trim, misaligned derailleur (bent hanger, or RD), and similar issues.

Often a system that ran fine before will begin to skip with new chain and cassette because the worn stuff was sloppy and forgiving and the new stuff isn't. Sometimes the chain was changed from one with nice bellmouth in the inner plates to one with less causing more sensitivity to slight trim error, especially with a new sprocket with sharp corners which are more prone to snagging.

Check the obvious, and if all seems OK, and the skipping isn't overly annoying, ride it a while and it may resolve with break in.

I recently posted with the same issue. It turned out to be a worn chainring. Are you sure it's skipping at the cassette?

Since the chain only skips on the cog you use the most I'd say that one cog is probably worn too much for the new chain to engage [roperly. You'll either need a new cog or most likely easier to just replace the cassette.

Cheers from MIele Man

What shifters do you have? IF you have some "other brand" shifters, such as SunTour, the indexing may be off.

Thanks for the comments.

The skip mostly appears to be a power skip (the sort that typically happens with a worn cassette). Pedaling load increases the probability of a skip. However, sometimes the chain seems to skip when I am not pedaling hard.

Note that the cassette and chain are both new, neither is worn. Also, the skip only happens on one sprocket, therefore ruling out the chainring (which is also fairly new).

I'm using Shimano trigger shifters and derailer, and Shimano-compatible SunRace cassette. All the alignment and adjustment seems perfect.

I plan to keep riding it and see if anything improves. If it doens't, I'll count it as a quality control issue and buy a new cassette. 7-speed cassettes are fairly cheap.

Update: Thanks to FBinNY for suggesting the trim issue. Shifting worked crisply in each direction on every sprocket, and the skipping problem only happened on one sprocket, so I hadn't considered that trim could be the cause.

But the skipping stopped after I backed out the rear derailer's barrel adjuster 1/2 turn.