· VINTAGE MOTORHEAD
I don't claim to be an expert on this subject, but I have run the same size racing slicks on different width rims. They always had the same overall diameter BUT, the narrower rim forces the sidewall "section" inward which does tend to round the tread. In other words, the tread area did not lay as flat on the narrower rim, rather it became convex. The center was higher than the edges. The tire will still roll the same distance. The wider the rim the flatter the tread will lay on the surface.