Wave goodbye to clicking, ticking gears on your bike ride with our guide to how to index your rear mech!
Let’s face it, there’s only one thing worse than forgetting to start Strava when you go for a ride, and that’s having to put up with gears that are slow to shift up and down your cassette.
Indexing your rear derailleur can seem like a tricky task, however, our guide will help you master the mech!
Where are your limits?
Firstly, it’s important to check the limit screws – these are the small screws at the rear of the mech, typically with ‘H’ and ‘L’ marked against them.
The limit screws determine the full range of movement of the derailleur, and so stop the chain from falling off the inside of your cassette, and potentially into your spokes – which is super dangerous as it can cause crashes – or to stop the chain falling off the outside of the cassette, towards your frame.
Here’s how to check the limits of your bike’s rear mech:
- Shift the gears so that you are in the smallest sprocket in the rear derailleur.
- By hand, push the mech all the way up toward the wheel until it reaches its full range of motion. Don’t push beyond this point or you will damage it! Check that the mech is directly beneath the biggest sprocket.
- Release the mech and check that it lines up perfectly with the smallest sprocket of the cassette.
- If the mech isn’t lining up perfectly with either the biggest or smallest sprockets, you need to adjust your limit screws. Depending on the make and age of your mech, this is typically carried out with either a cross head or Phillips head screwdriver. Our 8-in-1 Multitool includes a cross head screwdriver and our Mini Ratchet Toolset includes both types.
- You now need to adjust the limit screws so that the mech lines up perfectly at either end of the cassette.
- Adjust the ‘H’ screw to adjust the mech when the bike is shifted down to the smallest sprocket. Tune this up until the chain is perfectly in line with the small sprocket.
- Turn the ‘L’ screw to adjust the mech when the bike is shifted up to the biggest sprocket. Tune this up until the chain is perfectly in line with the large sprocket.
Now that you have got the limits correctly set using the process outlined above, it’s time to fine tune the indexing of your bike’s rear mech!
We now use the small barrel adjuster at the bottom of the cable, where it connects to the mech.
This increases or decreases the tension on the cable, which in turn alters how the mech moves up and down the cassette.
- Shift your bike into the small chain ring at the front and the smallest sprocket of the cassette.
- Shift up the cassette (towards the biggest sprocket) and observe how well the chain is moving up and down. If the gears aren’t working well you may notice it takes some time for the chain to get into the next sprocket, or doesn’t shift at all. If this shifting is ‘slow’ you need to turn the barrel adjuster counterclockwise (as you look on it from the back of the bike) until the shift is smooth. Rotating the adjuster counterclockwise effectively moves the entire mech toward the wheel.
- You then work your way up the cassette while still in the small ring, making small adjustments with the barrel adjuster as you go until the shifts are all perfect. Turn the adjuster clockwise if you need to move the mech away from the wheel.
- When you’re happy that you’ve achieved smooth, fast shifting through the gears when you’re in the small chain ring, check that the shifting when you’re in the big chain ring is also efficient and adjust as necessary.
Hopefully the two steps above will get your bike’s shifting sorted. However, fear not if it doesn’t!
There are some common issues that can prevent you from getting sweet shifting straight away. Below are the common things you may need to check out if you’re still struggling:
Bike still not shifting well? Possible problems:
How’s it hanging? Check your mech hangar.
Your rear mech hangar is designed to be quite easily bent. Whilst this may seem stupid, it’s to protect your rear mech – if you knock the bike, it will be your hangar, which is cheap and easily replaced, which takes the damage, rather than your more valuable derailleur. If your hangar gets bent, it affects how well your bike will shift.
Look at the mech from the back of your bike and it should be exactly vertical. If it has a bend in it, you have two options:
- If it’s only slightly bent, it should be possible to bend it back. Doing this requires a special tool and is a bit of an artform, so unless you’re comfortable working on the bike, get down to your local bike shop and get some help!
- If the hangar is very bent, or it’s been bent before, we recommend you buy a new one. Trying to fix it in this case could leave the mech very weak and liable to snapping, so it’s safest to just replace it. If you do need to replace it, you’re best off using a torque wrench to do so, to avoid any potential damage to your frame.
Worn out? Check your chain and cassette.
Your chain and cassette don’t last forever unfortunately. Lots of riding, or riding in particularly harsh conditions, will wear down these items, and if these are worse for wear you’re never going to have smooth shifting.
You can check you chain condition using a simple tool – check out our video guide below to see how to do this. If it’s worn, swap it out!
Checking your cassette simply requires a visual inspection. The teeth of the sprockets should be quite ‘square’ as opposed to sharp and pointed. Again, if it’s worn, replace it. If you need to change your cassette you should change your chain as well.