First, this seems like a great site and I hope to use it often. There is a bicycle company that is offering sprockets that they refer to as "decimal gearing". What the designer has dome is to slightly alter the Pitch Diameter (PD) and to then re-profile the sprocket teeth to prevent the chain rollers from interfering with the teeth. He claims that this decimal gear alters the 'effective' tooth count by up to .3 teeth. http://www.rennendesigngroup.com/Decimal.html We're talking about standard bicycle roller chain with a 1/2" pitch. 2 sprockets, one front, one rear. Nothing fancy. My belief is that a timed drivetrain is a timed drivetrain and that the ratio will always be determined by the number of teeth on the two sprockets. A 10t/10t combo yields a 1:1 ratio, regardless of any small variation in the PD. And in a sprocket with an under or over-sized PD, the chain rollers will have to alter their position relative to teeth throughout their engagement with the sprocket. This will cause loaded rollers to rotate, adding friction. Also, fewer teeth will carry the entire load, also increasing friction and wear. I simply cannot see how such a system could yield a ratio of anything other than that actual tooth count. If someone can confirm or rebut, I'd really appreciate it.