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When adjusting both front and rear derailleurs, which should be done first?

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    Do them in stages, going back and forth. – Daniel R Hicks Jun 9 '16 at 21:49
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There are three main steps to adjust both derailleurs. The first is usually not necessary unless the rear is very far out of adjustment.

  1. Adjust the rear derailleur enough that it will stay in the lowest and highest gears, even if you have to help it a little with finger pressure on the derailleur arm. This may require adjusting the high and low limit screws.
  2. Adjust the front derailleur: Start by putting the rear in one of your middle gears. Then run the front through each chain-ring and make sure that it will smoothly move from ring to ring. Adjust as necessary. Set the rear to the highest (smallest) gear. Adjust the front so that it does not rub in any of your 2 or 3 chain-rings. Set the rear to the largest (biggest) gear and repeat the tuning process. In a 2 chain-ring setup, you have to make sure that the cross chain combinations (small-small and large-large) don't rub either. In a 3 ring setup, it's not always possible or necessary. If you have 1/2 clicks on the front shifter (most often in 2 ring setups), make sure to include them in the process. If you can't seem to get the front to adjust without rubbing, it's possible the height and/or twist of the derailleur clamp has changed. Check manufacturer's recommendations for position, if so.
  3. Adjust the rear derailleur: Put the front in smallest ring in front and tune the rear derailleur until you are satisfied with the speed and quietness of the shifting. If it's noisy or grinds, it's not right yet. Don't forget about the B-screw when tuning. If it's out of whack, then your shifting will be difficult or inconsistent, depending on which way it's out of adjustment. Next, move to your next biggest chain-ring and repeat the adjustment process of the rear derailleur. If you have 1/2 click front derailleur adjustments, you will need to include them in your tuning process.

In a nutshell, adjust the front derailleur first, then the rear.

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6

If the derailers just need minor tweaking (they are basically in adjustment but are "not quite right") then you adjust the one that is obviously wrong, check the overall adjustment again, then again adjust what needs adjusting. Often only one derailer needs adjusting and often the adjustment is just a half-turn of the barrel adjuster.

If they are completely mucked up (but nothing visibly bent/broken), I usually first check the front for parallel and sprocket clearance (they often get knocked out of alignment), get it on the center sprocket, then address the rear. Once the rear is basically correct, get the front to where it will shift to all rings with modest accuracy, then, trying all combos, adjust the rear some more. Finally, fine-tune the front, then fine-tune the rear.

But it varies with the bike, how recalcitrant the derailers are, and specifically what is out of adjustment most.

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Answer: "Yes"

Every part of the system affects every other part of the system. So you could spend ages making the rear perfect, then go and tweak the front which puts the rear out again.

Like truing wheels, back and forth is your best answer to focus down on the best position for both.

Don't forget to clean everything before you do adjustments. Makes life easier.

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  • Can you explain how the front and rear affect each other? They are not connected to each other, unlike spokes that are pulling against other spokes. – ojs Jun 10 '16 at 16:38
  • @ojs you're right they're not connected by anything directly. However they both work to manage the one chain. My bike lacks any form of trim on the front mech (which is also a triple) so I get rub on the front cage. With minimum rub, I now can't backpedal in low gears without derailing the front chainring. So you can't flatly say "do front then rear" or "rear then front" it has to be an iterative process. – Criggie Jun 11 '16 at 2:13
  • The derailleurs are located on opposite sides of the cogs, so the the relative location of derailleur and chain depends only on shifter position, derailleur adjustment and which cogs the chain is on. The derailleur on opposite side can not change chain position, except by moving the chain to different cog. – ojs Jun 11 '16 at 9:50
  • @ojs I can only speak from experience, having to adjust one then the other and then go back and tweak the first one again. Repeat until correct. – Criggie Jun 12 '16 at 0:24
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    Our experiences are wildly different, and I can not find a rational explanation to your experience. – ojs Jun 12 '16 at 9:37
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It does not matter. The derailleurs are located on opposite sides of the cogs, so the the relative location of derailleur and chain depends only on shifter position, derailleur adjustment and which cogs the chain is on. The derailleur on opposite side can not change chain position, except by moving the chain to different cog.

It is far easier to adjust the derailleurs by sight, so that rear one lines up with cogs and front one has correct limits, than try iteratively adjusting until the shifting is smooth. If you want to do the latter, you may need to switch between front and rear.

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  • Your answer is not exactly correct. For example, if the rear is so far out of adjustment that it can not get to the highest or lowest gear on the cassette, then you will not be able to adjust the front properly. So while the adjustment of the derailleur only depends it's location, chain rub is affected by both front and rear positions and is a critical component of derailleur adjustment. – Scott Lundberg Jun 11 '16 at 12:13
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I learned that the rear should be adjusted completely first. The front is notoriously difficult to get just right.

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    But if the front isn't roughly correct then you'll never get the rear right. – Daniel R Hicks Jun 10 '16 at 11:04
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    Welcome to Bicycles! We're looking for answers with more detail. Please consider expanding your answer to further elaborate how you dial in the adjustment. A short answer like this is likely to get downvoted, flagged for moderator intervention, and possibly deleted. – Gary.Ray Jun 10 '16 at 14:45
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Start with the rear derailleur, then work your way up to the front. For a tutorial search for GCN on Youtube. They have a pretty good series of videos about this topic.

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  • Welcome to Bicycles! We're looking for answers with more detail. Please consider expanding your answer to further elaborate how you dial in the adjustment. A short answer like this is likely to get downvoted, flagged for moderator intervention, and possibly deleted. – Gary.Ray Jun 10 '16 at 14:44

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