Ten speed drivetrain, about 4000km on the chain and cassette. Shifting is perfect across the big half of the cassette but in the three smallest cogs it skips under pedalling load, roughly once every few pedal strokes, and it's fine if I soft pedal. I've indexed the barrel adjuster back and forth with no improvement. New cable and housing last winter. What's the likely culprit?
If a new chain doesn't fix it, look at the hanger. A bent derailleur hanger throws off the small cogs more than the big ones because the parallelogram is at the end of its travel there. A shop alignment tool costs nothing to have checked and eyeballing it does not work.
Had them check while the cassette was off. Slightly out, straightened, shifting is genuinely better than it's been in a year.
One more suspect for load-dependent skipping: the freehub. If it's the freehub pawls slipping you'll feel it as a sudden lurch with no gear change and it'll happen in any gear once it gets bad. Grab the cranks and try to force the wheel backwards — a bit of play is normal, a click that gives way is not.
Also check the cassette lockring is actually tight. It should be somewhere around 40Nm and hand tight is nowhere near that. A slightly loose cassette lets the small cogs move under load and produces exactly this symptom.
@flat_rate_finn · 3mo ago · 3 replies
Skipping under load only, in the small cogs only, at 4000km is a worn chain hooking on worn cogs. Indexing problems show up as hesitant or noisy shifts across the whole range, not as a load-dependent skip in one section.
Check the chain with a wear gauge or measure 12 full links — if that's stretched past about 1.5mm over 305mm, the chain is done. The catch is that if you've run it well past 0.75% wear it has already chewed the small cogs, which see the highest chain tension and the fewest teeth, so a new chain alone will skip worse on the old cassette. At 4000km on a commuter in the wet, replace both.
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@two_stroke_tess · 3mo ago
Gauge dropped straight in at 0.75 and nearly at 1.0. New chain and cassette, skipping gone completely. I'd convinced myself it had to be cable stretch.
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@hive_tool_hal · 3mo ago
Buy the cheap two-sided wear gauge and check every couple of months. Swapping a chain at 0.5% means the cassette lasts three or four chains instead of one.
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