Learning how to adjust gears on a bike can save you unneeded trips to the bike shop and ensure your bike will run smoothly and quietly every ride. If you feel like the chain is sluggish when shifting between gears or there is a considerable amount of noise caused by the chain rubbing on the various parts of the mech, then just a few minor turns on the barrel adjuster can save the day. 

Adjustable parts on the rear derailleur

There are four main adjustment points on any rear derailleur, no matter the brand or discipline. 

1. High and Low limiting screws that set the upper and lower limits for how far the derailleur can move the chain up and down the cassette 
2. B-tension screw that sets the distance between the upper pulley wheel and the cassette
3. The barrel adjuster that adjusts the cable tension when indexing your gears
4. The clamp screw that secures the shifting cable

To be able to work with these various screws, you will need to have on hand a two- and four-millimeter Allen wrench, and a Phillips screwdriver. Which one of these tools you’ll need for which bolt generally depends on age and brand of the derailleur.

Setting up the rear derailleur for the first time

The limiting screws are very important to have properly adjusted. They prevent the derailleur from over-shifting the chain off the cassette. Normally you shouldn’t need to adjust these screws often, only on initial set-up and perhaps when you have changed cassettes. 

They are identified with an H for high and L for low. The H screw corresponds to the smallest cog, and turning the screw will allow you to align the pulley with the smallest cog. Shift into your smallest cog. If you can see that your pulley is out of alignment, then turn the H screw clockwise to move the pulley back towards the inside of the cassette while turning it counterclockwise will move it towards the outside of the cassette.

Similarly, adjusting the L screw will align the pulley with the largest cog and prevent the derailleur from throwing your chain into your spokes. 

These are times when you will appreciate having a bike stand since it will allow you to see more clearly the alignment. It will also make it easier to test your adjustments by pedalling through the gears. If you don’t have a bike stand, turning the bike upside down will help, but just keep in mind which direction you will be turning the screw may be reversed. 

Indexing bicycle gears

Once you have set your H and L screws so that the derailleur is perfectly aligned in the high and low position as regards the cassette, you can start indexing the gears. Indexing the gears means that each click of the shifting lever will cause the rear derailleur to move the chain one cog. 

To do this, put the chain in the smallest cog. As you turn the pedal, try shifting up to the next cog. If the chain grinds and hesitates before moving up, or even refuses to move up at all, that means you need to tighten the tension on the shift cable. Turn the barrel adjuster counterclockwise to increase the tension. Do not turn it too much initially. Never adjust it more than one full turn before checking to see how much improvement that makes. 

Once you’ve made the adjustment with the barrel adjuster, try shifting up to the next cog again. If the chain is still rubbing or not shifting quickly, turn the adjuster again, and continue to check how much that improves the shifting. When the chain moves smoothly and noiselessly from the smallest cog to the one above, continue shifting up the cassette to ensure each shift onto the cog above is equally smooth and quiet. 

Then shift down the cassette to ensure you have not tightened the cable tension too much. Sluggish shifting down the cassette is a less common shifting issue, but if you find that it is a problem for you, simply turn the barrel adjuster clockwise to reduce cable tension. We recommend when you are trying to reduce the tension that you never turn the barrel adjuster more than a quarter turn before testing. 

Keep in mind, if your shifting cables are brand new, you may notice the shifting become sluggish and imprecise after you’ve ridden them for a few hundred miles. That’s due to the new cables stretching a touch. Once that happens, simply follow the same method to retighten the cable to improve the shifting performance. 

Setting the B-tension screw

The B-tension screw controls the distance between the upper pulley wheel and the cassette. Typically, that distance should be about 6 mm measured from the pulley to the largest cog on the cassette. However, some manufacturers define exactly what that measurement should be, so be certain to check the instructions if you are setting your gears up for the first time.

To set this distance, shift into your largest cog in the rear and the smallest chainring in the front. If you want to increase the distance, rotate the B-tension screw clockwise and counterclockwise if you want to decrease the distance. If you have had to make extensive adjustments to the B-screw, take just a minute to shift through your gears again to make certain the indexing is still spot on. 

Adjusting the front derailleur

If you are experiencing poor shifting between your front two chainrings, then you can adjust your front derailleur to make sure every shift is smooth. Perhaps the chain is reluctant to shift up onto the large chainring, or it is dropping off the chainrings all together. To fix these issues, you’ll use a similar methodology that you’ve already used for the rear derailleur. 

That’s because a front derailleur has several adjustment points that will allow you to ensure everything is in its right place and working order:

1. High and Low limiting screws that set the upper and lower limits for how far the derailleur can move the chain on and off each chainring
2. Derailleur clamp bolt that sets the height and angle of the front derailleur
3. The cable clamp bolt that defines the cable tension 
4. Cable barrel adjuster which sits further up the cable, usually near the head tube, where finer adjustments can be made for indexing

When setting up your front derailleur for the first time

If you are putting the front derailleur on for the first time, then using the derailleur clamp bolt you’ll need to make certain that it sits just about 2 mm above the top tooth of the big chainring. If your derailleur has already been set up properly for you, then you probably won’t need to readjust this, unless you have changed the chainring sizes. 

The angle of your derailleur is also controlled from this bolt, and that might need readjusting. For instance, if you have had your chain shifted off the outer ring and jammed on the outside of the crank, then the derailleur angle might have been knocked out of whack. The angle should be parallel to the outer chainring. When you loosen the clamp bolt, you will be able to adjust the derailleur orientation to be in line with the chainring.

Both of these measurements are worth a double checking if your shifting has gone all wonky. Once you have established that both the derailleur height and angle are properly set, then it’s time to focus on the indexing of the shifting.

How to index the front derailleur shifting

First check the cable tension at the cable clamp bolt. Shift into the small chainring and check the tension in the front cable. If it feels taught, then you can move onto the next step. If it is slack, then you will need to loosen the cable clamp bolt and tighten the tension before retightening the bolt. 

Now you should check whether you can shift from the small to the large chainring. If that is still sluggish, then you can micro adjust the tension in the cable using the barrel adjuster by turning it counterclockwise. Increase the tension with a quarter turn each time and then check how smoothly the chain can shift into the big chainring. 

Don’t forget to set the limiting screws 

Once you have the cable tension set properly, then shift into the smallest chainring in the front and the biggest cog in the rear. If the derailleur and chain are rubbing on the inside, turn the L screw (the one closest to the frame) counterclockwise to move the inner plate of the derailleur so that it is about 1 mm away from the chain. Turning the screw clockwise will move the derailleur back out if you screw too far inward initially. Once you have this screw set, then you should not hear any chain rub or drop the chain when shifting down. 

To adjust the upper limit or H screw, shift into the largest chainring in the front and the smallest cog in the rear. Turn the upper limit screw clockwise until there is a 1 mm gap between the chain and the inside of the derailleur outer plate. 

Conclusion – a silent chain is a happy chain

It’s never difficult to tell when your shifting needs adjusting. Sluggish shifting, over shifting, under shifting, and noisy shifting are all the most common and irritating signs. Thankfully mechanical groupsets all come with adjustable bolts and screws that are designed to make it easy even for the novice mechanic to keep the drivetrain running smoothly. 

If you have followed these instructions and are still suffering from shifting issues, then there may be other issues causing the problem. A worn chain, overused cogs and chainrings, frayed shift cables, and worn-out small parts within the derailleurs and the shift levers can all be the culprits. In such cases, you may still need to make a visit to your trusted mechanic at your local bike shop. 

But having the knowledge of how the front and rear derailleur move and work will give you the power to make essential adjustments without having to resort to professional help. It may seem maddingly fiddly, but it’s a skill that will help ensure smooth shifting throughout all your rides.

Be sure to also check our article on how to adjust a bike saddle.