I have a 2x6 drive train on an '85 Fuji Del Rey. I'd like to put on smaller chain rings for touring but am unsure what I can get away with while still using the short cage Suntour LePree RD and LePree FD.

As I read the archives here, I see that there are two issues at play: First, that you can only get away with about 28 teeth worth of difference with a short cage derailer. Second, that the FD can only make so big a jump between chainrings.

So, how far can the 28 tooth rule be pushed and how big a jump can a mid quality old school front derailer make happen. If you have suggestions for the optimal ring sizes for such a touring setup, I'm all ears.