997.2 GT3/RS steel rotors direct bolt in replacement of 997.1 GT3/RS PCCB rotors
05-26-2010, 04:37 AM
#16
Thanks for everyone's interest in this retrofit.
As both cfjan and Carrera GT deduced from my original post the rotor fits over the hub just fine. No issues with spacing or offset. The 997.2 GT3/RS steel front rotors are dimensionally identical to the 997.1 PCCB rotors in how they fit over the hub and align laterally (using the plane of the axle as the z axis) in the caliper.
The difference is the alignment in the horizontal, front to rear, or x axis of the caliper brake pad surface. The PCCB rotor is a true 2 piece design (consumable CC friction ring mounted to a reusable aluminum hat) while the 997.2 GT3/RS steel rotor is a one piece construction (steel friction ring wedded to an aluminum non reusable hat- see below).
The alignment issue is a result of the void between the hat and the friction ring in the 997.2 GT3/RS steel rotor. With out shimming the caliper ~2.5mm away from this void the anterior (inner) brake pad surface would impinge in this area (apparently there is a Porsche service bulletin about this) while the posterior (outer) brake pad surface would be too far from the outside edge of the friction ring. Shimming out the caliper properly aligns the brake pad surface and friction ring for optimal performance.
I am not certain why the void between the friction ring and hat section exists. If I guessed it would be a function of weight savings and cooling efficiency. What ever the reason for the void it makes the alignment of the brake pad and friction ring more critical for the 997.2 GT3/RS steel rotor than for the 997.1 GT3/RS PCCB rotor (PCCB rotor has more friction ring surface area than the 997.2 GT3/RS steel rotor due mainly to this void). When I have a chance I will measure the 997.1 PCCB take off rotors and compare to 997.2 steel.
BTW- some people have requested part numbers for the 997.2 GT3/RS steel rotors. They are listed below;
P997-351-409-91 (left front)
P997-351-410-91 (right front)
P997-352-405-92 (rear; not certain if left or right)
P997-352-406-92 (rear; not certain if left or right)
My cost was $504.90 each for the fronts and $489.16 per rear (total $1988.12).
As both cfjan and Carrera GT deduced from my original post the rotor fits over the hub just fine. No issues with spacing or offset. The 997.2 GT3/RS steel front rotors are dimensionally identical to the 997.1 PCCB rotors in how they fit over the hub and align laterally (using the plane of the axle as the z axis) in the caliper.
The difference is the alignment in the horizontal, front to rear, or x axis of the caliper brake pad surface. The PCCB rotor is a true 2 piece design (consumable CC friction ring mounted to a reusable aluminum hat) while the 997.2 GT3/RS steel rotor is a one piece construction (steel friction ring wedded to an aluminum non reusable hat- see below).
The alignment issue is a result of the void between the hat and the friction ring in the 997.2 GT3/RS steel rotor. With out shimming the caliper ~2.5mm away from this void the anterior (inner) brake pad surface would impinge in this area (apparently there is a Porsche service bulletin about this) while the posterior (outer) brake pad surface would be too far from the outside edge of the friction ring. Shimming out the caliper properly aligns the brake pad surface and friction ring for optimal performance.
I am not certain why the void between the friction ring and hat section exists. If I guessed it would be a function of weight savings and cooling efficiency. What ever the reason for the void it makes the alignment of the brake pad and friction ring more critical for the 997.2 GT3/RS steel rotor than for the 997.1 GT3/RS PCCB rotor (PCCB rotor has more friction ring surface area than the 997.2 GT3/RS steel rotor due mainly to this void). When I have a chance I will measure the 997.1 PCCB take off rotors and compare to 997.2 steel.
BTW- some people have requested part numbers for the 997.2 GT3/RS steel rotors. They are listed below;
P997-351-409-91 (left front)
P997-351-410-91 (right front)
P997-352-405-92 (rear; not certain if left or right)
P997-352-406-92 (rear; not certain if left or right)
My cost was $504.90 each for the fronts and $489.16 per rear (total $1988.12).
As for not shimming the pad out to the periphery of the ceramic rotor, I would never want to experiment. The leverage is real, but I'd say immeasurably infinitesimal. And the risk of a heat dispersion issue is not to be toyed with.
05-26-2010, 08:29 AM
#17
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Can't answer that directly. I am looking forward to using the retrofit set up over the Memorial Day weekend and gaining insight under operation. It will be interesting to experience the difference between the two rotor constructions on track as well as see how the pads and friction rings wear over time.
05-26-2010, 01:48 PM
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06-08-2010, 10:17 PM
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The RS was exceptional on track. Far easier to drive fast than I anticipated. My overall level of satisfaction with the car and set-up is greater than I hoped.
Regarding the 997.2 GT3/RS steel rotors retrofitted to the car they performed flawlessly over 3 - 25 minutes sessions around the 2.4 mile Mid Ohio circuit. Wear of both the pad and rotor is as anticipated with no heat checking on the rotor. The wear pattern indicates the alignment of the pads to the rotor is spot on (caliper is spaced out from the hub accurately).
I can't say I like the Carbotech XP10 pads that were recommended to me as much. I prefer PFC 01 compound in the front and PFC 97 for the rear calipers. The PFC has a better initial bite than the Carbotech and better modulation properties (for the record the factory brake fluid fill was flushed and replaced with Castrol SRF). Regardless the rotors did their job and any concerns re: compatibility are resolved for me. Time will better my perspective but my educated guess is that my satisfaction will persist.
