Looking for smooth shifting? Here's our full guide on how to index your gears. Poorly set up gears is an infuriating problem. You'll find that either you'll skip gears or not change gear at all when you push the lever. Thankfully it's an easy issue to fix. Gears shift based on tension in the cables, which are adjusted via the barrel adjuster - you'll find it where the gear cable meets the rear derailleur. Small adjustments here will put more or less tension into the system and help solve your shifting problems. If you find the chain falls off your cassette when you shift into the highest or lowest cog, take a look at your limit screws. They essentially stop the mech from going too far over, which is what causes the chain dumping in the first place.