I have an IRO model 19 (eccentric bottom bracket) and am currently running a 33 by 16 drivetrain. This gearing has proven a little too tall and I'd like to lower it a bit. I tried a 17 tooth rear cog but, couldn't tension it properly with either the existing chain or, a new, longer one. I discovered that I'd likely need a half link in the new chain. I would like to move to a larger cog while maintaining the functionality of the EBB adjustment (which I like very much) and not have to use a half link chain. I've heard about the "magic" gear combinations and don't really get it, I also don't want to go through multiple cog/chain combinations either. Can someone recommend a cog that would accomplish my goals? I seem to remember someone at IRO telling me that an 18t cog would work but, it's been a long time and can no longer get in touch with them to confirm.

Thanks,