How to tune a Rear derailleur step by step,assuming that there is no damage to your frame, gears or cables. If in doubt, check out our troubleshooting page for more info.
Dont get hung up First things first, get your rear wheel of the ground in such a fashion that you can turn the pedals and easily reach the shifters and derailleurs, a workshop stand is great but you can improvise with rope tied to the rafters, or hang your bike off a low hanging branch or rail by the seat (get creative). It is REALLY useful to have your bike the right way up for this job. Once you are happy that your bike is reasonably secure, it is time to start tuning.
Get in tune Start off by shifting your rear derailleur (RH shifter) into the hardest gear (smallest cog on rear wheel) whilst turning the pedals with your hand.
1) Undo the pinch bolt two turns on your derailleur so that the cable is loose.
2) While rotating the pedals, turn the H screw clockwise until the derailleur starts to shift into the next gear up, then back it off so the chain is happy on the smallest cog.
3) While turning the pedals, carefully push derailleur up and let it fall back into place, it is reluctant to fall into smallest gear, loosen H screw and repeat until it returns easily.
4) You have now established the upper limit screw which sets up the rest of the gear tune.
5) Screw in the barrel adjuster (found on either the derailleur or shifter) clockwise until it done up snug, back it off two turns.
6) Pull the cable end firmly and tighten pinch bolt (doesn't need to be crazy tight, just snug).
7) While turning the pedals at an approximate normal riding cadence, give the shifter one click. If the chain doesn't move up a gear, wind the barrel adjuster out a 1/2 turn and start again. Repeat until one click of the shifter = one gear change.
8) Set the lower limit by turning the L screw clockwise most of the way in.
9) Shift through the gears gently until the shifter stops. You will probably be in the 2nd or 3rd gear from the biggest cog.
10) Turn L screw anticlockwise 1\2 turn at a time until you are able to shift into the biggest cog, but no further.
11) Now with both of your outer limit screws set up you can tune using cable tension.
12) Shift through the gears. If it is slow to shift from smaller to bigger cogs, tighten cable by winding barrel adjuster OUT. If it is slow to shift from big to small cogs, loosen cable by winding barrel adjuster IN.
13) By now your gears should be shifting well on the rear cassette. If they are not, go back to the troubleshooting page as there might be something that need repairing or replacing. Remember even the best bike mechanic can't tune broken gears.
14) Take you bike for a test ride and readjust cable tension as necessary (things may settle into place over time).