A silent and smooth-running transmission can make all the difference to your ride.
The videos below explain how to diagnose and fix common shifting problems and the techniques within them apply to both road and mountain bikes.
How to diagnose common drivetrain problems
The first thing to do is find out what's wrong with your gears. The video below shows you what to look out for when you've got misfiring gears. Watch it here or read the summary beneath.
Problem: Gears won't shift up or down perfectly with one click
Solution: This is most commonly caused by stretched gear cables and you will need to re-index your gears. The second video in this article explains how.
Problem: Gears are well indexed but the chain keeps dropping off of either end of the cassette or chainrings
Solution: This is most commonly caused by poorly set up derailleur limits and these will require adjusting. See the third video for an explanation on how.
Problem: My rear gears are properly indexed, but the chain shifts too far in one direction
Solution: If the chain won't run to the bottom of the cassette and shifts over the big cog into the spokes (or vice-versa), it sounds like a bent rear hanger needs straightening or replacing. If you've been in a crash or damaged the bike somehow, this is the likely cause. The final video below explains how to do this.
Problem: Down-shifting is fine but upshifting is sticky or slow
Solution: When were your cables last replaced? Dirty cables and housing can cause slow or inaccurate shifting.
Problem: Chain slipping, jumping and generally misbehaving
Solution: Inspect your cassette, chain and chainrings for wear. Can you see a pointy shark-fin-like profile on your cog teeth or chainrings? We're sorry to say, but that sounds like you may need to replace your chain, cassette and chainrings.
Indexing your gears
If the gears on your bike are properly indexed, each click of the shifter will cause a single shift up or down the gears, front or rear. If you find you’re skipping a gear or that your shifting is getting stuck, then there’s a good chance you need to adjust your indexing. Indexing problems can be caused by cable stretch, which is a normal part of the bedding-in process for new bikes or cables.
Check that a bent or damaged rear derailleur isn't to blame first. If it's all good, here's how to index or re-index your gears.
What you need
A hex key to fit your derailleur cable retention bolt, usually a size 4 or 5mm.
What to do
Step 1: Shift your front derailleur into the middle or smallest ring, then wind your rear barrel adjuster in fully clockwise, then out one turn. Release the cable mounting bolt on the back of the derailleur.
Step 2: Pedal gently, and push the derailleur until the chain moves up to the second-smallest cog, then stop pedalling. Pull the shifter cable taut and retighten the retention bolt, taking care not to overtighten it, which can cause the cable to fray. Pedal gently and the chain should return to the smallest cog, then test the indexing by using the shifter to move through the cassette.
If upshifting is hesitant, gradually increase cable tension by turning the barrel adjuster a quarter turn anticlockwise and trying again. If your bike overshifts, reduce the cable tension by turning your barrel adjuster clockwise until the chain runs smoothly in the second smallest cog.
If upshifting is responsive, but downshifting isn’t, then there’s a high chance the problem is dirty inner cables or housing, in which case you should try lubricating them or replacing them.
Step 3: Shift your front derailleur to the smallest ring and your rear to a cog near the middle of the cassette then slacken the front derailleur cable by winding the barrel adjuster fully clockwise. Release the cable retention bolt, take any slack out of the cable and then re-tighten the cable retention bolt.
Attempt to shift to the middle or outer ring. If shifting is hesitant, wind the barrel adjuster one half turn anticlockwise before pedalling again. Repeat this process until the chain steps up cleanly onto the bigger ring. If you have a third chainring, try upshifting to it and add another half turn if shifting is still hesitant.
Once you’re happy with your upshifting, drop back down through the rings to check your downshifts.
Setting derailleur limits
Limit screws control the range of movement of a derailleur. If they’re not set properly, then your chain may be able to drop from the cassette or chainrings, which can be dangerous — for both you and your bike.
Before getting started, ensure that your derailleur hanger hasn’t been bent. If it is, you’ll need to fix or replace it — see the video below for how to do this.
What you need
A small crosshead screwdriver
What to do
Step 1: Locate the lower limit screw, which will be marked with an ‘L’, and screw it fully clockwise. Push on the derailleur to manually shift up to the highest gear possible — this should take you to the second or third biggest ring on the cassette.
While still manually pressing on the derailleur, gently turn the cranks and wind out the low (L) stop screw until the cassette shifts to the biggest cog and isn’t jumping or clicking.
Step 2: Wind out the high (H) adjuster and allow the chain to move towards the bottom of the cassette by pedalling gently. Wind in the high adjuster until the chain returns to the smallest ring/highest gear and runs smoothly without jumping or clicking.
Your rear high and low limits should now be set.
Step 3: Adjust your jockey-wheel clearance by locating the screw on the top-rear of the derailleur. This adjustment is referred to as the B-tension or 'dangle-angle'.
With the bike in the highest gear, the upper jockey wheel should run just clear of the cassette. Turning clockwise will increase the gap, anti-clockwise will close it. Adjust until there is about 2mm of clearance.
Step 4: Shift the front gears to the smallest ring and the back gears to the largest cog. Fully wind in the front derailleurs low limit (L) adjust screw.
You should complete this procedure with a slack gear cable, so you can be sure that cable tension isn’t overriding your low limit setting. To do this, release the cable retention bolt on the derailleur. Slowly turn the pedals and wind out the screw until the chain returns to the small ring and runs smoothly, without rubbing on the derailleur cage.
Pull the slack from the cable and re-tighten the retention bolt, not so tightly that you fray the cable. Wind in the high limit (H) stop screw. Shift the rear gears to the smallest cog.
Pull on the gear cable manually, not with the shifter. You can use a tyre lever to pull on the cable, so that it doesn’t dig into your hand.
Keeping pressure on the cable, wind out the screw a half turn at a time until the chain jumps to the biggest ring. After this, quarter turns will allow you to adjust the derailleur so it doesn’t rub the chain.
Your high and low stops are now set, but you will probably need to make adjustments to your front indexing using the barrel adjuster.
Replacing a bent rear derailleur hanger
Derailleur hangers are sacrificial parts that are specifically designed to bend or break in the event of an impact to prevent more costly damage to your derailleur or frame.
If your rear shifting isn’t working properly and your bike has suffered a knock — in a crash or while loading into a car, for example — then there’s a good chance your hanger is bent.
Bending a hanger is easily done, which is why we’d recommend always carrying a spare with you on the road or trail, as well as a multitool with the right size hex keys.
Any hanger will work with any derailleur, but you might need to do some research to find one that is compatible with your frame.
Don’t be tempted to try to bend your hanger back to shape during a ride, because it’s likely to break, leaving you with a long walk home. Instead, you could try readjusting your rear derailleur limits and indexing, by following the videos above, to compensate for the misalignment. This might not give you access to your whole cassette, but it’ll get you home.
Assuming you have a spare to hand, here’s how to install it.
What you need
- Appropriately sized hex keys
What to do
Step 1: From behind the bike, sight the line of the chain as it runs over the cassette and through the upper and lower jockey-wheels. All three should be arranged in a straight line, and if they’re not, you’re going to have to go ahead and replace the hanger. Bends towards the wheel are the most common, though outward misalignment is possible too.
Step 2: Remove your rear wheel. Then remove the derailleur from the hanger, allowing it to rest on the chain.
Step 3: Next, undo any bolts connecting the hanger to the frame, taking care not to lose them.
Reverse this process to fit your new hanger, quickly check your limits and indexing, and you’re ready to ride.