OK. Thanks for the information. The analogy of stacking two coins slightly off center is a good one (helps me visualize what I am dealing with on my inner roadwheels). On some of my outer roadwheels, I think I see the 'effect' that Dodgy is talking about: it looks more like a 'ghostly' line running through the circumference of the wheels. And at first, I was trying to get rid of them, but I don't think there is really anything to sand away...
I have a couple more miscellaneous questions here that I don't know if warrant their own threads so I pose them here:
1) How can I get rid of the sprue attachment points on my road wheels? For a time I was attempting to sand them away. But in looking at them under 10x magnification, I clearly see that some of them are 'incuse', sunk into the surface of the wheel. This is surprising to me in that I am very careful to use sprue cutters and modeling knife to cut off my road wheels with plenty of extra sprue 'sticking out' (that I thought I could then remove with knife and sanding). Alas, I'm not sure how to get rid of these sprue attachment points...
2) I have plenty of extra modeling knife blades (I use No. 11's), but I am wondering if I should be replacing my blades more frequently? Put differently, how many blades does a competent modeler go through, say completing an average 1/35th scale tank kit? I have read that if one cuts photo-etched/metal parts, the knife of course dulls more quickly. And I suppose if one is doing a lot of scraping (say of road wheels), it behooves one to replace blades more frequently, too?
Thanks in advance for explaining!