It's probably not a good idea to have mirrors visible from other than the standard cockpit cameras. If you have mirrors visible in external cams, it means that for 20 cars, the GPU has to render all 20 mirrors at the same time and all their different views. I would imagine it would have a massive impact on FPS. Or maybe it's not that big of an issue with today's GPU power, who knows. I think once the game sees "Mirror.BMP" or MIRROR in some material, it automatically tags them inactive on external cams.
