Originally Posted by
sjanzeir
Convention being the operative word here...
FWIW, I have one of those Grimeca rotors in the OP on my bike and I have mounted it the "wrong" way around, i.e. with the spokes pointing forward (and the markings facing inward, just like in the second picture in the OP.)
I'm pretty sure that's the way Grimeca intended. They are using a very common spoke pattern, which I've never seen mounted the way their arrow points. But this has made me curious as to why this kind of directional spoke pattern is commonly used, as opposed to a radial pattern. A quick Google didn't help, so obviously not a common question. Neither are there any horror stories of assploding rotors mounted the wrong way.
I would think it is all about putting the spokes in tension, which is why they are invariably mounted with the spokes pointing forward. If you mount them that way then the spokes will tend to straighten out under load. If you mount them as per the arrow, the spokes will tend to collapse under load.