A silent and smooth-running transmission can make all the difference to your ride.
The four videos below explain how to diagnose and fix common shifting problems.
The techniques within them apply to both road and mountain bikes.
How to diagnose bike gear problems
The first thing to do is find out what's wrong with your gears. The first video below shows you what to look out for when you've got misfiring gears. Watch it here or read the summary beneath it.
Video: How to diagnose gear problems
Problem: Gears won't shift up or down perfectly with one click
Solution: That sounds like you've got yourself some stretch on new cables there and you 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 either end of the cassette
Solution: an easy fix, this one: adjust the derraileur limit settings. See the third video for an explanation on how.
Problem: Gears are properly indexed, but 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 straigtening 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 grippy
Solution: When were your cables last replaced? Because that sounds like a simple case of muck and grime in the housing.
Problem: chain slipping, jumping and generally misbehaving
Solution: Inspect your cassette, chain and chainrings for wear. See a pointy shark fin profile on the cog teeth? Sorry, but that sounds like you need to replace the chain and cassette.
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 and 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
Video: how to index your gears
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.
Pedal gently, and push the derailleur until the chain moves up to the second-smallest cog, then stop pedaling. 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 then gradually increase cable tension by turning the barrel adjuster a quarter turn anticlockwise and trying again.
If upshifting is responsive, but downshifting isn’t, then there’s a good chance the problem is dirty inner or outer cables, in which case you should replace them.
Shift your front derailleur to the smallest ring and your rear to a cog near the middle of the cassette. Slacken the cable by winding the barrel adjuster fully clockwise. Release the cable retention bolt. Take the slack out of the cable and retighten the cable retention bolt. Then 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 hesitant.
Once you’re happy with your upshifting, drop back down through the rings to check your downshifts.
Setting derailleur limits
Limit screws control 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 – both for 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
Video: how to set your derailleur limits
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.
Gently turn the cranks and wind out the LOW stop screw until the cassette shifts to the biggest ring and isn’t jumping or clicking.
Wind out the HIGH adjuster. Allow the chain to move towards bottom of the cassette by pedaling gently. Wind in the high adjuster until the chain returns to the smallest ring/highest gear and runs cleanly without jumping or clicking.
Your rear high and low limits should now be set.
Adjust your jockey-wheel clearance by locating the screw on the top-rear of the derailleur.
With the bike in the highest gear, the upper jockey wheel should run clear of the cassette. Turning clockwise will increase the gap, anti-clockwise will close it. Adjust until there is about 2mm of clearance.
Wind in both screws as with the rear derailleur
With the rear in the biggest ring/lowest gear, drop the shifter to the lowest ring at the front. Wind out the screw until the chain drops to the granny ring and runs cleanly with no clicking or rubbing.Next, drop the rear to the smallest/highest gear and shift on the bars to the biggest ring – if you can. If not, wind out the screw until it will click up. Then quarter turn at a time, wind out the screw until the chain runs clearly with no rubbing.
Check the stops by pulling on the cable to insure it doesn't move further and drop off the top.
Shift the front gears to the smallest ring, and the back gears to the largest cog. Fully wind in the low 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 retighten the retention bolt, not so tightly that you fray the cable. Wind in the high 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 used on mountain and road bikes and specifically designed to bend or break long before your frame or derailleur, in the event of an impact.
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 has bent.
It’s easily done, which is why we’d recommend 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
Video: How to replace a bent rear derailleur
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 toward the wheel are the most common, though outward misalignment is possible too.
Remove your rear wheel. Then remove the derailleur from the hanger, allowing it to rest on the chain.
Next, undo the two small hex 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.