Left and right 996 brake rotors

Does anyone know why the front left and right brake rotors on 996 C2s have different part numbers? The rears have the same part numbers. Is there a difference between the L and R front rotors? If so, what is the difference?

They are directional therefore different. You need to buy both parts for correct fitment.

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BOOM! +996

To expand, the configuration of the ventilation "vanes" in the interior of the rotor are directional. They work far more efficiently to cool the rotor when the rotor rotates in the designated direction. Your fronts will heat up and fade far too quickly otherwise. The rears supply far less braking force and generate much less heat hence those rotors can be bi-directional.

02TX996Cab: Thanks, that makes sense.

Good responses stating the fronts are directional, but then why aren't the rears?

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Remember, it's less costly to manufacture non-directional rotors; therefore, if most of the braking power is in the front of the car, then non-directional should not see the heat cycles like that of the front. Therefore, it's more marketable in my opinion. The rear are still vent as you know, but not the fan-like pattern.

To my understanding the front brakes have directional fins internally to help with the cooling of the rotor. Thus having a different part number reference to differentiate left and right. As b3freak said the front brakes do most of the work and create stopping power thus generate more heat. Then the rear brakes have radial or straight veins inside which do not need to be directional or improved cooling flow.

Device2: great illustrations. For conversations sake - Seems as though the cooling would be better if the rotation were the opposite of the picture. Since the vanes would "bite" into the wind if they "leaned" into the direction of the rotation?

The brake rotor with the canted cooling fins acts like a fan and pumps air from the center and expels it from the OD of the rotor.

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Jasile, Unless I'm mistaken, Porsche brake rotors use the principle of a centrifugal fan to promote air movement thus keeping the brakes cooler and more effective. When the blades are curved backwards (like the picture), air that naturally enters the fender well is pulled through the wheel and through the rotor vents to promote cooling. If you were to reserve the rotors, air from the rotors, would be forced outward (through the wheels), fighting incoming air. The arrangement would be counterproductive to the cooling process as hot air would get trapped around the rotors.

b3freak, is correct Jasile. Here is a better illustration of the centrifugal design and cooling. Here is how the ram air is directed to the cross drilled rotors and why the "bite" effect is perhaps not better, when they designed the airflow to expel the heat. As opposed to ingesting it and causing turbulence in the cooling flow. Here is a picture of the ram air fin attached to the front suspension arm to assist with the cooling ram air flow.

Great responses from all. I hadn't considered that the air would travel from the inside of the brake out vice outside to in. Pictures speak a thousands words. Great illustrations Device 2.

Yes excellent responses & I wish the PO of my car had read this, as the garage advised me that my fronts are on the wrong side on mine. I need to swap them over & fit new pads as the wear patterns will be different! 'WAM' (What A Muppet!) Hope that is the worst mistake I find.

For future reference, the rotors are stamped L and R or will otherwise be marked - you won't ever repeat previous owner's mistake since you can read; drag that PO couldn't.