streetpirate, I have built a bike based on the same exact excercise bike you have. It is a blast. That gearing will be equivelant to my 3rd gear. I am running 26" wheels. I pretty much only ever use 3rd when I have a tail wind.
I may be interested in your chainring and fixed gear wheel if you are not going to use them.
I am out of the challenge since mine's done, but here is a link to the thread and my most recent picture. Can't wait to see what you guys come up with.
those are some sweet bikes! I will probably throw the big chainring up for sale soon, might hang on to the fixed wheel a little while, try out a 20" fixie and see if I would ever ride one. Right now I'm seeing a bmx style scooter, but it's still going to be a couple of weeks before I start cutting so plans might change back to something with pedals