How to Adjust a Rear Bicycle Derailleur by Revolution Cycles

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Have you ever had troubles with your bike switching gears unexpectedly or not shifting correctly? Many people have this problem, but are afraid of attempting to fix it for fear of adding to the problem. But you don’t need to go into the shop to get your bicycle shifting properly. Just adjust the rear derailleur! A good eye and some lubricant should be all you need.

1) Shift the bike to the lowest possible gear (largest gear sprocket on the rear cassette, this is the one closest to the spokes).

2A) Look at the rear cogs (sprockets) and make sure they are not touching the derailleur cog/top pulley (guide pulley) when in the lowest gear. This is very obvious as it causes a very loud noise when the bike is being pedaled in this gear.


If the cogs are in contact with the cassette, then turn in the derailleur alignment screw (“b” screw or chain gap adjustment screw) clockwise to increase tension until the cogs are separated from the cassette by at least a couple millimeters (1/10″).

2B) If the cogs are too far from the cassette, loosen the alignment screw until they touch, then tighten it until they just clear a few millimeters.


3) Feel for tension in the lower cable, this should be tight when the detailer is set in the highest gear. (Smallest gear sprocket on the rear cassette, this is the one furthest away from the spokes and closest to the derailleur).


4) Shift to the highest gear and observe from behind how the chain rides on the smallest cog. If it looks like it might come off towards the axle, tighten the “H” screw clockwise until it looks centered. Likewise, if the chain looks like it’s rubbing on the next gear, loosen the “H” screw. To make sure you are adjusting the correct screw; carefully watch the derailleur as you turn the screw, as the derailleur should move with just a fraction of a turn of the correct limiting screw. Then readjust the cable tension until shifting is smooth again.


5) Shift to the lowest gear to make sure that the chain does not fall off the cassette. As in the previous step, watch how the chain rides on the cog (this time you’re focusing on the largest cog). If the chain seems like it is leaning towards the spokes, tighten the “L” screw clockwise. If it looks like it wants to shift down, loosen the “L” screw. Test your adjustments by shifting through all the gears again.


6) Attempt to shift through all of the gears in both directions so you can diagnose whether it is shifting properly. If the bike is having trouble shifting down (shifting to larger rings; chain hugs the smaller cogs) then tighten the cable tension by screwing the tension screw out (counterclockwise) a little bit at a time until it is shifting properly. If the bike is having trouble shifting up (shifting to smaller rings; chain sticks too close to the larger cogs) then loosen the cable tension by turning the tension screw clockwise in a small amount.

7) Lubricate the screws and pivot points. Keep the chain lubricated with special chain lube to ensure that stiff chain links do not affect the shifting, and to make sure that the drivetrain will last.


Helpful Tips

  • Always check to make sure the derailleur hanger (where the derailleur attached to the frame) is not bent, as it must be bent back before attempting to adjust the derailleur.
  • Wipe away excess lube so that dirt does not collect on it.
  • In some bicycles, the positions of the “H” and “L” screws (the limit screws) are reversed.
  • Adjustments should be made in quarter-turn increments.


  • Failure to properly adjust the rear derailleur can cause the chain to slip off and potentially damage the frame and possibly send the derailleur into the rear wheel.
  • Unless you are an experienced mechanic this may be difficult to do. The Team at Revolution Cycles Dubai will welcome you in store to show you how to adjust if you feel a little uneasy doing it yourself for the first time.

For more info, please call or email: 4 3697441

Words by: Stewart Howison

Photos by: Keith Perena

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