Originally Posted by
mihlbach
Not exactly. The difference of one tooth on either your cog or ring will move the axle 1/8". For example, subtracting a cog tooth decreases the circumference of the cog by 1/2 inch. The chain only goes half way around so the chain has 1/4" less contact with the cog. That gives you 1/4" of slack. Divide that in half again to account for the upper and lower parts of the chain and you have 1/8".
You are right, my bad. It was a typo on my part, 1 tooth on the cog is only 1/8, not 1/4. Had to admit my mistake as we know Sheldon couldn't have been wrong!