Medium cage derailleur capacity?

[EndoMaster]

How can I tell, other than actually doing it, what front/rear ring combo will work with a medium cage derailleur? I know that there is a formula that can be used to figure this out.

Thanks in advance for the help.

 

[tkblazer]

i believe you can't use a big ring front and a 34 tooth rear cassette or at least that gearing.. i only have two rings up front with a bash guard, so i don't have a problem running a med. cage rear derailluer

 

[EndoMaster]

i believe you can't use a big ring front and a 34 tooth rear cassette or at least that gearing.. i only have two rings up front with a bash guard, so i don't have a problem running a med. cage rear derailluer

I have a 2x9 setup as well but I was looking to replace my front 32 with a 34 or maybe even 36 once the 32 is worn out. I wanted to figure out if the mid-cage derailleur would take up the extra chain slack that's created by a longer chain needed for a larger front ring.