Quote Originally Posted by bcipam
All this engineering seems alittle over my head but have you considered mountain bike components for your rear derailleur? I have Ultegra shifters and front derailleur but run XTR gear on the rear - gives me a 30 - 34 ratio. Very low. You will have to buy a rear derailleur as well as a cassette and new chain. But for $200, a good fix (Although uncertain how this all fits in to what you have done already...)
Good point. My touring bikes also have mixed components - Ultegra front and XT or XTR rear. I definitely couldn't get the gearing I wanted with all road components. I remember when I had my first touring bike built - the frame builder was initially thinking I should go with mountain components until he realized that the mountain component groups didn't have the (shorter) crank length that he was recommending.