In racing stuff where you have a true file fit ring that you custom fit to each cylinder, the overall ring diameter can't be more than about .005 larger/smaller than the bore of the cylinder, or the rings radius will be too large/small to seat all the way around the cylinder. If you have a .010" or .020" oversize ring and your cylinder is .030" overbore, those rings will have a radius too small to work, even if you get the gap where it needs to be.
