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I'm rebuilding an old bike and have an existing crankset with 52-42-30 chainrings. I'm looking for a front derailleur. Most of the triple front derailleurs I've come across say they don't support a 50 tooth chainring.

According to the documentation I've been able to find, the Claris triple front derailleurs are designed for 50 tooth chainrings and the mountain (Acera and others) are specified as supporting 48 tooth or lower depending on the models.

Sheldon Brown states

If you use a front derailer with a larger ring than it is meant for, the rear of the cage will get too close to the chainring before the front of the cage is close enough to provide crisp shifting.

What is the tolerance for this in practice? Can I use a derailleur designed for 50 tooth? Would a 48 tooth one be close enough, since I might be able to find a 48 tooth one at a better price?

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According to Shimano front derailleur specs here all road triple front derailleurs support max 50 tooth and have 20 tooth capacity (max difference between largest and smallest rings).

The general consensus on this site is that Shimano is quite conservative in it's specifications so overstepping the max chainring and capacity by 2 teeth will probably work OK.

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    You could also peruse sale sites (ebay, Amazon, smaller ones focusing on bike parts like you might find on facebook) and obtain a somewhat older model front derailleur. I still enjoy good performance of the stock setup on my '05 Trek 1000 in which the Shimano FD-2203 moves the chain smoothly between the 52-42-30 Bontrager crankset. Sheldon Brown also wasn't afraid to shape front derailleur cage plates with an angle grinder so they'd run noiselessly despite being imperfectly matched to the chainrings. – Jeff May 26 at 10:45
  • I have a 1999 Sora 52-42-30 crankset. The original Sora front derailleur wore out and the LBS replaced it with a new Claris triple a couple of months ago. It works fine. – Gabi May 28 at 4:33

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