Ok thanks for the help. Is there any reason why I can't just choose the chainring/cog combination that I want and then shorten my chain until it fits? can't be that hard surely... I mean how accurate does the chain tension need to be? Is it 1/8" sort of movement in the axle or even less?
cos by altering cog sizes I can get it within 1/8" and using half links I can do 1/4"...