After attempting a steep grade in my new hilly home today, I realized I need lower gearing for a century comming up in two weeks. I also don't mind sactificing my topmost gear, so I think I might change both chanrigns.

Currently, I'm running Hyperglide 13...28 in the back. In the front, I have 42,52 Biopace. I'm tending towards choosing a smaller set of chainrings rather than a larger casette. First, I'd like to get of the Biopace. My questions...

So far, on combination that creates the lowest position for the chain at the FD, I have about 12 mm of clearence between the chain and the bottom of the FD. Any idea how small of a chainring I can get without needing to move the FD? The bike is older and I'd rather not need to move the FD.