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Unless your bike has an electronic groupsets, chances are your drivetrain and/or brakes still depend on a properly fitted and adjusted set of steel cables and outer cable housing to function. These cables have been used on bicycles for a long time for several good reasons:
They are cheap to manufacture
They are reliable, easy to adjust without special tools
… and easy to find pretty much everywhere!
While electronic groupsets are cycling technology marvels that do away with cables, chances are the average home mechanic isn’t equipped with the tools or the skills to work on them. In contrast, physical cables are fairly straightforward to adjust, and even if you encounter issues with your drivetrain or brakes mid-ride, it is often fairly straightforward to quickly fix the issue if it is cable-related.
In this article we explain how setting the right cable tension is critical for a well-tuned drivetrain, and how to fine-tune cable tension using barrel adjusters.
Understanding cable tension
Your drivetrain (or cable-actuated disc or rim brakes) relies on cable tension to properly function. Without the cable tension being in the correct range, derailleurs will not shift correctly, brake pads might rub on braking surfaces and all manner of issues may manifest themselves in the form of little mechanical annoyances we are familiar with.
Cables also stretch overtime and require periodic re-adjustment. When fitting a fresh set of inner cables and outer housing, cable tension is primarily set at the pinch bolts that secure the inner cables to derailleurs or brake calipers. Fine-tuning the tension, however, is often done using a small yet critical part known as the barrel adjuster.
What is the barrel adjuster and where to find it on the bike?
A barrel adjuster is a small cylinder-shaped piece, usually with some kind of serrations or knurling that makes it easier to grip, used to adjust tension on your bike’s cables. Barrel adjusters are tool-free parts. That is, they are designed to only be manipulated using your bare hands, and using tools like pliers on them might actually damage them.
Barrel adjusters are found on a few locations on the bike, depending on the type of frame you have and whether it has external cable routing with cable stops or internal cable routings. To find your barrel adjusters, start by looking where your derailleur cables go into the bike and trace the path of the cables down to the derailleurs. Possible locations will include:
On the shifters: You will find it right at the point where the shift cable enters the shifter. This is common on trigger shifter pods used on mountain and other flat-bar bikes, as well some older road bike shifters.
On the rear derailleur: common on road rear derailleurs, but not all mountain bike derailleurs.
On cable stops: this can often be found on some road bike frames, usually on the first cable stop on the downtube.
In the middle of cable housings: these are called inline barrel adjusters. Sometimes these are used for front derailleur adjustment where there are no other points for installing barrel adjusters on the frame.
On rim brake calipers and mechanical disc brake calipers and levers: the barrel adjuster will be located on the caliper itself, at the cable entry point. With mountain bike mechanical disc brakes, there is often a barrel adjuster at the lever.
How to use barrel adjusters to index your shifting:
If the chain is hesitating to shift to larger cogs (or from small to large chainring), then you need to add cable tension by turning the barrel adjuster counter-clockwise.
If the chain is hesitating to shift to smaller cogs (or from large to small chainring), then you need to reduce cable tension by turning the barrel adjuster clockwise.
How to use barrel adjusters to fine tune your rim or mechanical brakes:
The basic theory is the same. Assuming your calipers are centered and initial slack taken out of the cables, you can turn the caliper or brake lever adjuster clockwise to reduce cable tension, or counter-clockwise to add cable tension. This can be used to bring the pads closer to the braking surfaces for a more immediate braking action at the lever, or micro adjust the caliper clearance to prevent brake rub.
Important tips for using the barrel adjusters:
It is easy to add excessive tension with barrel adjusters, but just as easy to undo it. If you use the barrel adjuster and the chain jumps two cogs (or pedaling becomes noisy due to the chain rubbing on the next cog up the cassette), back out the adjustment by a half-turn to bring the tension down just enough to make a clean single shift.
It is important to remember to make small changes using the barrel adjuster. Start by one full turn. If the problem persists, add or remove cable tension in half or one full turn increments.
You can do it while riding, but maybe you shouldn’t…
While it is entirely possible to use the barrel adjusters to fine tune your shifting while riding the bike (assuming the location of the adjuster is accessible from the riding position), please prioritize safety while riding and do not risk having your attention focused on adjusting your gears and not on the road.
If barrel adjuster tweaks don’t fix it…
A bent or misaligned derailleur hanger
Cable is set too loose at the anchor point to begin with. Reset initial tension by loosening the cable anchor bolt, pulling the cable and retightening the anchor bolt
Incorrectly adjusted derailleur limit screws
Incorrectly fitted parts, such as the front derailleur sitting too high or with an incorrect angle on the chain
Old, frayed or corroded inner or outer cables that need to be replaced
Kinks or sharp bends in your cables that cause excessive friction
Excessively dirty or worn drivetrain
In the case of rim or mechanical disc brakes: Misaligned or off-center brake calipers