There was just a thread about this so I know the answer
11-30
Also as a bunch recommended on the other thread, you could do a subcompast crankset (46-30 or 48-32) to get that 1-1 or close enough.
oh, I just rememebered this
http://www.interlocracing.com/casset...oad-cassette-1
there is a 32T and a 34T max cassette that IRD makes