chain length?
 

My chain works for a 53-39 with a 12-17 cassette, but I'm wondering if a 11-39 cassette would help with the massive bank of america inclines I have around here, thanks!!!

I'm guessing you meant to say you have a 12-27 cassette.

Yes, you'll have to increase the chain length to use that 39t cog and where the heck did you find a 11-39 cassette? :)

But more importantly you'll probably need a new rear derailuer to accomodate it unless you already have a long cage MTB derailuer.

[on the other hand, you might have meant using an 11-29t cassette which you should be able to fit without issue]