Bike Gears & Derailleurs
Gear problems have a reputation for being fiddly, and they earn it mainly when people adjust things in the wrong order. There are four possible causes of bad shifting, and only one of them is the barrel adjuster everyone reaches for first.
These guides work through diagnosis before adjustment, then cover the full setup sequence for both derailleurs and how to shift well enough that the drivetrain lasts.
What you'll learn
- Work out whether the problem is cable tension, friction, a bent hanger or wear
- Index gears with the barrel adjuster in quarter-turn steps
- Set rear derailleur B-tension and the L and H limit screws in the right order
- Position a front derailleur by height and rotation before touching a screw
- Stop the chain dropping off the chainrings
- Shift without crunching, and understand which gear combinations to avoid
Guides in this topic
- How to Adjust a Front Derailleur
Set a front derailleur in the correct order — height, rotation, then the L and H limit screws and cable tension — so it stops dropping the chain.
- How to Adjust a Rear Derailleur
Index a rear derailleur in the right order: hanger alignment, B-tension, L and H limit screws, then cable tension at the barrel adjuster.
- How to Shift Gears on a Bike
Which shifter does what, when to change gear, why you should ease off the pedals, and the cross-chaining combinations worth avoiding.
- How to Adjust Bike Gears
Diagnose bad shifting before you adjust anything: cable, limit screw, hanger or wear. A symptom-led guide to getting bike gears indexing cleanly again.
Common questions
Why are my gears not changing properly?
Most often cable tension has drifted, which a quarter turn of the barrel adjuster fixes. If shifting is bad across the whole range, suspect cable friction, a bent hanger or a worn chain instead.
What do the H and L screws do?
They are mechanical stops that limit how far the derailleur can travel at each end of its range. They do not affect shifting between gears — that is cable tension.
Why does my chain rub in some gears?
In the most extreme combinations — big ring with the largest sprocket, or small ring with the smallest — the chain runs at a severe angle and light rub is normal rather than a fault.
Related topics
- Chain and drivetrain
Clean, lube, shorten, remove and replace a bike chain, plus cassette cleaning and dropped-chain fixes — including the wear figure that saves your cassette.
- Cleaning and tune-ups
Wash your bike without forcing water into the bearings, and work through a full home tune-up checklist that finds problems before they leave you walking.