Workshop skills: How to adjust your rear derailleur

Ever taken one look at your bike’s rear derailleur and thought, ‘no, I’ll pay someone to do that,’ instead of attempting some maintenance yourself? Well, it might be easier than you thought to learn how to do it yourself – adjusting the rear derailleur isn’t that hard. Here’s what you need to know.

In a rare act of harmony in the cycling industry, all the derailleurs are adjusted in essentially the same way, from Box to Campagnolo, all derailleurs have the same basic anatomy.

shimano-xt-rd-m8000-rear-derailleur-shadow+-11sp-medium-IRDM8000GSEvery derailleur is connected to your bike via a hanger. A hanger is a piece of sacrificial metal that is designed to, in the event of a crash, break before your derailleur or frame does. If your bike is shifting roughly after a crash, or after you’ve haphazardly thrown it in your car, 9 times out of 10 it’s going to be an issue with the hanger. All the indexing and cable changing in the world won’t help this. You generally won’t be able to eyeball this, but the cardinal sign of a cactus hanger is gears that only shift terribly on a few cogs. You’ll need to replace or realign this before your bike shifts cleanly again.

IMG_1178

Hangers vary for almost for almost every bike model, making them a pain to track down, so when you do need to buy a hanger, get more than one. It’s a fairly common issue, so keep a spare handy.

If your bike still grinds worse than a learner driver’s first time in a manual when you haven’t crashed, or after you’ve replaced your hanger, then you’ll need to index your gears.

There are four majors ways to adjust your rear derailleur: the B-screw, the high and low limit screws, and the barrel adjuster.

B-screw

If your mech won’t change into the highest gear, or makes a terrible noise when you do, you may need to adjust your B-screw.

The B-screw sits directly behind the hanger and adjusts the angle at which your derailleur sits. This adjusts the distance between the top jockey wheel and the cassette. To shift cleanly, the top jockey wheel needs to sit 5-10mm below the bottom of the largest cog. Shift into the highest gear possible and turn the screw out, counterclockwise to increase this distance, or clockwise to move the derailleur closer.

Limit Screws

If you can’t shift into either of the extremes of your cassette, or your chain falls off the cassette at either end, you’ll need to adjust your limit screws. Remember, you’ll only be able to set your limits if your B-screw is set correctly.

Every derailleur has two limit screws. The high limit screw (the top screw for Shimano, bottom screw for Sram, and right screw Campagnolo) adjusts the distance toward the smallest cog your derailleur will move. In the smallest gear, adjust the high limit screw until the jockey wheel sits directly below the smallest cog.

The low limit screw (the bottom screw on Shimano, top screw for Sram and left screw on Campagnolo) adjusts the distance toward the wheel your derailleur will move. This screw is imperative to get right, as shifting into your wheel is a great way to ruin a wheel and a derailleur. Without adjusting your shifter, push the rear derailleur into the largest cog, then adjust the low limit screw until the jockey wheel sits directly below the largest cog.

Barrel adjuster

If your hanger is straight, your B-screw is correct and your limits are set, and your bike still feels like it rides rough, you’ll need to check your barrel adjuster next. On a road bike you can generally find the barrel adjuster at the derailleur end of the outer cable, and on a mountain bike it’s generally at the base of the shifter. The barrel adjuster alters the tension on the cable. Turning the barrel counterclockwise increases the tension, and clockwise decreases the tension. Shift into the smallest cog, and the little ring in the front, and then perform one, clean upshift. If the chain doesn’t cleanly move into the next gear, tighten the barrel until it does, with touching the shifter. Perform another upshift to test how the chain moves to the next cog. If it doesn’t move cleanly, tighten the barrel adjuster. Then change back to the smallest cog and repeat the process on the three smallest gears until the mech shifts cleanly. Then shift through the whole block, tightening where needed.

If the mech is struggling to shift into smaller gears, you’ll need to loosen the cables by twisting the barrel adjuster clockwise.

As with any skill, fine tuning a derailleur takes some skill and time, but the more you do it, the better you’ll get. It can be helpful to learn how to do your own adjustments, and also save you money, which means more spare money to spend on your bikes!

About Tim_Davis@Pushys

I'm a Science Graduate and Medical student at the University of Queensland, specialising in anatomy and physiology. More importantly, I'm all for any type of riding; road, mountain, dirt jumping, I love it all! Let me know if there is anything you want to know about nutrition and health, and I'll do my best to help you out!

4 Responses

  1. Jeffrey Prickett

    Tim what angle should your derailer be to the cassette. I have struggled to find any info on this. Is it paralell to it vertically and sqare to it horizontally ?

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  2. Jeffrey Prickett

    And will the pressure or your derailer clutch will that bend the hanger during use. I’ve already replaced my hanger once but the new hanger has slowly gone out of original setting. The hanger is made of aluminium, if i try to bend it back to original position doesn’t that weaken the hanger ?

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