There are so many variables you can't really say. Firstly, you've got to consider the quality of the cranks, ISIS spline, bb trueness. For instance, I've been using an Onza 18T sprocket for about 3 years on about 5 different cranks. Every time I change my cranks or bb, the chain tensions in a different place, and gets loose in another. The freewheel is another problem. Recently, Monty have started welding up their freewheels. Ever since, the freewheels have stopped turning smoothly. Some are ok but the majority aren't which suggests that the chainring itself isn't perfectly round. Maybe I've just got a bad batch, but the quality seems to be dropping. One customer actually received a freewheel with a cut through sidewall so the bearing was exposed from the inside. I'll take some proper pictures of that when it's returned to me.