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I need to replace the front derailleur on my tadpole trike. Unfortunately, I cannot find a brand name or other numbers anywhere on the derailleur, so I cannot just replace it with an identical product. When looking at new items, they have many numbers and measurements which I do not understand, so I do not know whether I will be buying one that fits.

  • It has three gears.
  • The back derailleur is an 8-gear Shimano Deore.
  • I use MicroSHIFT shifters.
  • The other bike parts appear to be in metric.
  • The post that the derailleur clamps onto measures 28 mm in diameter.

What details do I need to look for to know that a replacement will be the right size for this bike?

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  • Edited to add recumbent trike tags and modified title.
    – RoboKaren
    Commented Jul 25, 2017 at 16:28
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    Two solutions - take the old FD into a Local Bike Shop and ask for "one of those please" If you have a bike cooperative in your city you can try the same there, often for a donation.
    – Criggie ♦
    Commented Jul 26, 2017 at 5:25

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Recumbent / trikes tend to use mountain-bike shifting equipment because they need the extra gear range. While there is a difference in cable pull between road and mountain sets, front shifters on the whole tend to be much less picky than rear shifters about chain width because essentially the limit for front shifting has stayed at 3 chainrings (aside from @Criggie with his 4 chainring setup). While it is optimal to try to match the chain width (speed), it is not a necessity. As always: Sheldon Brown

That means you can use pretty much any (Shimano) mountain bike triple front derailleur that fits. The main consideration for you will be how to mount the front derailleur. If you're using a clamp mount, you have to have one that can fit the tube where the derailleur mounts (the 34.9mm in the examples below are the seat tube thickness but many times the derailleur will come with a variety of clamps and shims to match different tube sizes). If you have braze-ons, they need to fit the braze-ons.

The other consideration is where the cable pull comes from (from the top or bottom of the derailleur as it would be normally mounted on a standard bicycle). Many front derailleurs allow for pull from either direction (dual pull) but some like the SRAM below are "top-pull only" or "bottom-pull only."

Amazon example

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    I've never bothered matching FD to chain width - as long as it fits the seat tube or mount, and has enough lateral range then its workable. Remember the Front Derailleur is a brute-force mechanism because it has to move a chain under tension, and its not a lightweight fine control like the rear mech.
    – Criggie ♦
    Commented Jul 26, 2017 at 5:23

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