Originally Posted by nlerner
I say go for the 24-tooth cog; it'll give you a low gear of about 41 inches, which should help on the hills, and a high gear of 73. You might find yourself riding in high gear on the flats a great deal, but you'll improve your spinning technique! I'd also suggest you splurge for a new chain.
Neal
From what I have heard with an S-A hub you don't want to go lower than a 41" low gear because it can destroy the hub.