Also check that the rear derailleur can accommodate the difference in teeth (22 chain rings or 26 with the 22 tooth granny plus 23 if using an 11-34 cassette = 45 or 49 with the granny). If this is too much for the derailleur, you could decide to not use the extreme cross-chain combinations (or get a longer arm derailleur).
However, one nice thing about recumbents, particularly long wheel base recumbents, is they allow a large amount of cross-chain due to the long length of chain minimizing the angular differences at the chainring and cassette.
Edit: For example, the SRAM X.9 rear derailleur has a capacity of 37 teeth for the medium cage length and 45 for the long cage.
Last edited by Giro; 06-07-09 at 12:46 PM.