A well maintained bike is satisfyingly crisp and sharp in its shifting, whilst gears that are playing up can really interfere with your ride. The good news is that most shifting problems you come across involving the rear gears are easy to adjust, and a little careful tweaking will make all the difference.
Bike gears are cable operated – the rear gears use a derailleur to shift between sprockets on the cassette, adding to or reducing resistance.
Over time cables can stretch and need a little adjustment. If you begin to find that your rear gears make some funny “clunking” noises or sometimes don’t work in certain cogs, this could mean you need to give them some TLC.
You will need a bike stand, and a screwdriver for this.
If your bike is not shifting into the smallest or biggest cog: Adjust limit screws
The ‘limit’ screws control the inward and outward movement of the derailleur – ensuring you can shift from the biggest and smallest sprocket, but also stopping the chain from over-shifting, which causes the chain to come off the sprockets sometimes hitting the wheel or frame.
If the limit screws are poorly adjusted, you will find you either can’t use your smallest cog (hardest gear), largest cog (easiest gear), or your chain comes off at either side, smacking the frame or wheel.
The screws are marked ‘H’, and ‘L’. ‘H’ controls the outer limit, shifting into the smallest sprocket (the one that provides the most resistance), and ‘L’ controls the inner limit, shifting into the largest sprocket.
Adjusting the H-Limit Screw
1) Shift the chain into the largest chain ring using the front gears, and the outermost (smallest) cog using the rear gears.
2) Turn the cranks with the pedal at a reasonable speed (around 60rpm or more), and shift up a gear on the back, to the second smallest cog, then back to the smallest.
A) If the chain drops into the gear fine, leave it and move on to the L-Limit screw – your H-Limit screw is doing its job
B) If the chain fails to go into the smallest cog, clatters or clunks, turn the limiter H-Limit screw anti-clockwise by one quarter of a turn to loosen the cable
C) If the chain goes to the outside of the smallest cog, turn the screw a quarter turn clockwise, to tighten the cable
3) Repeat step 2 – if the chain still fails to shift as it should, try another quarter turn. Keep doing this until it works – but only ever turn the screw by one quarter at a time
Adjusting the L-Limit Screw
1) Shift the chain to the smallest or middle chain ring on the front gears, and to the second innermost (second largest) cog using the rear gears.
2) Turn the cranks using the pedal, then shift up to the biggest cog.
A) If the chain shifts to the next gear comfortably, skip to ‘barrel adjustment’ – your L-Limit screw is fine.
B) If the chain clunks or it’s hard to get into the biggest cog, turn the L-limit screw half a turn counter-clockwise.
C) If the chain goes too far and jumps off the cogs, turn one quarter clockwise.
3) Repeat step 2, and add another quarter turn if it’s still not working until the adjustment is correct. Only turn the screw in increments of quarter turns, a tiny movement can make a big difference.
If your middle gears aren’t shifting or are clunking: Barrel Adjustment
Now that your limit screws are set up properly, it’s time to tackle the gear changing between the cogs that make up the rest of the cassette.
You’ll know this needs doing if you find them when you tell your bike to shift into some gears, it clatters and rumbles until you select another gear. You don’t have to put up with this – it’s easy to fix.
The barrel adjuster is the small barrel beneath the derailleur:
1) Shift the chain into the middle of the cassette.
2) While rotating the cranks, using the shifter move to a larger cog. If the chain does not shift to the larger cog, it clatters, clunks or seems unwilling, turn the barrel adjuster half a turn anti-clockwise.
3) Shift down again to the middle cog again and repeat the shift to the larger cog – if the movement is easy, your problem is solved. If not, repeat step 2 until you get an easy shift.
4) Position the chain on the cog one above the middle, and rotate cranks at reasonable speed. Use the shifter to move down one cog, to the middle. If the chain does not shift down or is slow to drop to the smaller sprocket turn the barrel adjuster clockwise and repeat the test.
5) Continue until the movement is crisp, and your shifting problems will be over..
Assuming there are no other issues with your cables or derailleur – your bike should now be shifting beautifully. If you’re still having issues, you may have dirt the cable housing, a bent derailleur hanger, or another problem. If the shifting is inconsistent, the cables probably need renewing and may be fraying somewhere internally causing a variable amount of cable pull. All of these are perfectly easy to fix, but it might be time to do some more research, or visit your local bike shop.