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I'm thinking of buying a new derailleur in the future, but I don't know what type of derailleur to buy, there's long and short cage derailleurs but is there any differences?

I'm not sure if this helps but I have a Shimano Dyna 3x chainring that I recently converted to 1x, by that I mean I've removed the highest and lowest gear. The current drivetrain I'm using has 32 teeth.

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    The length of the cage mainly determines the "tooth capacity" of the derailer -- the total difference in sprocket sizes (as determined by tooth count) between minimum and maximum gear selections. Having an unnecessarily long cage, however, slightly reduces the precision/responsiveness of shifting. – Daniel R Hicks Feb 3 '19 at 13:46
  • is it possible to use a wrong derailleur? if yes, what will happen? – Lam Munn Jun Feb 3 '19 at 13:55
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    If it's too short the chain may jam or it may be impossible to shift to certain gear combinations. (On older bikes this was actually a "feature" -- you had to remember which combos you could use.) If it's too long you can have problems with the cage bumping into stuff (though only in extreme cases). – Daniel R Hicks Feb 3 '19 at 13:59
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    The longer the cage the sloppier the shifting. The longer the cage the greater the risk off the cage getting caught in the spokes (not a pretty sight). – Daniel R Hicks Feb 3 '19 at 14:13
  • I provided a generic answer, if you edit your question to add info on your current drivetrain I (or others) can provide a more specific answer. – Argenti Apparatus Feb 3 '19 at 15:07
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Cage length is part of the derailleur design that determines it's total capacity - the ability to take up chain slack when shifting onto small sprockets or chainrings.

If you look at the Shimano rear derailleur specs page you will see that the the 'GS' medium cage models have a higher total capacity than the 'SGS' long cage models. Long cage models are generally for triple chainring setups or cassettes with very large sprocket size spreads.

When looking at a replacement derailleur you need to look at the total capacity and the largest rear sprocket supported. The total capacity needs to be equal to or more than: (difference in tooth count largest and smallest sprockets) + (difference in tooth count largest and smallest chainrings).

It's best to pick the shortest derailleur that meets your needs, the shorter cage has more leverage and tensions the chain better. They also have a lower profile and are less likely to hit branches or rocks or other obstructions on the trail.

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  • i recently converted from 3x to 1x chainring. is it necessary to buy a derailleur with a shorter cage? – Lam Munn Jun Feb 3 '19 at 15:08
  • Not necessarily. If the current one is not giving you any problems why replace it? If you want to fit a larger range cassette at some point retaining the longer cage derailleur may make sense. There is no hard rule here. Shorter cage derailleurs perform a little better but they are not required. – Argenti Apparatus Feb 3 '19 at 15:19

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