Your question, and the answers posted above, appear to be based on the direction of the drilled holes. From what I know of brake rotors, the direction of the drilled pattern isn't the issue. The drilled holes don't dissipate heat, they are for looks (unless you have racing pads that produce gases, not a factor on the street). What dissipates heat are the fins. Furthermore, the fins impact the steady-state heat capacity of the rotor, while what is more important is thermal mass. The mass has been reduced by drilling holes, thus meaning that while the rotors can cool faster, they will also attain fading temperatures faster. This isn't usually important in street driving, and they do look nice.

Some rotors have cooling fins (the fins between the two friction surfaces) that are flat, or radial. Those rotors can be mounted in either direction. If a rotor has curved fins, then it is directional. Mounted the wrong way, the rotor will not have the same cooling characteristics and performance will suffer (unless you drive high speed in reverse all the time). The fins aren't designed to work like a ram air scoop, they are designed to encourage the air stream to draw air out through the rotor edge.

It is difficult to tell from your pictures which way the fins are running (I assume they are curved). The problem is that the drilled pattern may or may not match up with the fin pattern. Often, a rotor that is designed to have holes or slots has a heavier fin, and the hole pattern runs the same way as the curved fin. The holes are then spaced around the fins. If a rotor wasn't designed to be drilled, but is drilled afterwards, the theory is that the hole pattern may intentionally go opposite to the fin pattern, so as not to weaken the rotor too much, which causes cracking. While all this is somewhat theoretical, you then have to add in the fact that the company drilling the holes may or may not know or care about this. Brembo rotors with holes/slots can be made that way by Brembo, or modified by a third party. See all the low priced offers on ebay. Hence, it is anyone's guess what yours look like where the fin is.

Check the fins. See if they look like the picture below. All of the above means that you may have a different appearance front to rear (in terms of the drilled hole pattern) but both may be mounted correctly.

Jeff

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2007 X3 3.0si, 6 MT, Premium, White

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