Originally Posted by mihlbach

You should think this through more carefully...its more like 1/8" per tooth. I recently went from 42/15 to 45/16. I added a total of 4 teeth and I added 1 chain link and got the exact same axle position. Adding 4 teeth = 1 link = 1/2" axle movement. Therefore, adding or removing 1 tooth = 1/8' of axle movement. Sheldon says the same somewhere on his site. The reason its 1/8" and not 1/4" is because the chain only goes roughly around half the cog and chaing ring...the other half doesn't effect the position of the axle. Adding 1 tooth = 1/2 greater sprocket diameter. Chain only goes around about half of that, which means their is only 1/4" more contact of the chain and sprocket. Now divide that in half for the top and bottom portions of the chain and you only get 1/8" axle movement.