# Determining front derailleur capacity?



## PseuZQ (Mar 27, 2002)

OK, so i got the rear pretty much figured out....

But with front, when they say max capacity is 23t, is it just a matter of subtracting your largest rear cog from the number of teeth on the big ring? 

Like, 53 less 27 (biggest rear cog) is 26. (But who'd want to be in that gear anyhow? )

Seems like it's the max it could take without ugly, inoperative cross-chaining. 

Help? Please?


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## neil0502 (Feb 11, 2005)

I think the max capacity of a FRONT derailleur would be 

(# teeth in big ring - # teeth in smallest ring)

So ... on a standard double: 53t - 42t = 11t
On my Campy triple: 52t - 30t = 22t
On my Cannondale T2000: 48t - 24t = 24t


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## PseuZQ (Mar 27, 2002)

So would a derailleur with 23t capacity thus be incompatible with a 53-39-30 and a 12-27? 
Or would it work if I just stayed out of gear combos past 53/23?


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## neil0502 (Feb 11, 2005)

It isn't about the cogset at all.

Only about the crankset/chainrings.

A 23t capacity FD will work fine with a 30/39/53 triple. You SHOULD stay out of the cross-chain combinations regardless.

More info ... courtesy of Sheldon Brown:

http://www.sheldonbrown.com/derailleur.html


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## PseuZQ (Mar 27, 2002)

Ah, NOW i get it. Thanks!


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## denmikseb (Aug 7, 2005)

It is just the tooth # difference between largest and smallest chain rings.


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