Front derailleur adjustment

So, greetings everyone.

I have a JPWeigle that I am looking to change the chain rings on. The 53 & 39 were originally on there for racing (it has a 12-26 eight sp. cassette). I like the cassette, and it has thousands of miles left on it. If I chuck on 48 & 36 tooth rings would I have to lower the front der. any?

If it matters the mechanism is a Shimano 105 STI set up.

 

Chances are the bolt diameter(130mm?) means that the smallest inner ring you can mount is a 38t. If ya put on a 48t, yes, lower the FD so that the outer cage is about 1mm above the big ring.

 

You don't have to do anything if you don't care how poorly the front derailleur shifts the chain ...

If you want to maximize the shifting's efficiency, then you will want to lower the front derailleur so that the bottom of the outer plate of the derailleur cage is a couple of millimeters above the teeth on the outer chainring -- observe the current gap and try to reset the front derailleur accordingly with the smaller, outer chainring.

 

I'll have to check BCD...forgot all about that. Still, a 38T wouldn't be a deal breaker.

 

Thanks for the replies. They are as I suspected, but I always seek validation of my opinions.