Here is my thoughts. Mirror drag savings can be in the range of CD 0.01 or even more if your current mirrors are bad. To reach this with your own mirrors you should avoid few things and try to do what you can to make as sleek as possible.
1. Size is bad. So try to make mirrors as small as possible. I will use wideview mirrors in my Lupo. Smaller mirrors also reduce the frontal area. My Lupos mirros have about 1/3 of the original mirrors size and the original ones were already pretty small.
2. Shape. Mirrors should have the teardrop shape, because that is optimal. If you can build there the sharp teardrop end its even better. There might be even better shapes for mirrors if you study them at wind tunnel but best quess is teardrop shape.
3. Position is also important. Now this is my own thinking here. I think they should be as low as possible if you attach them to doors apillar corner. Reason is simple all the flow will come to that "mirror" corner from the hood and windshield so you dont want to disturb it more than you have to. In almost all modern cars the "leg" of the mirrors is as low as possible. If you dont care about the visual looks so much you can build it even lower.
Few pictures of the current state of my mirror project, scroll to the right for more mirror images. Tomorrow the story will continue with more images.
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