Miata Club w/ 12.88" GWR rotors pulsating on track

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Miata Club w/ 12.88" GWR rotors pulsating on track

Postby MichaelE081 » Fri Jun 25, 2021 4:19 pm

I have a 2021 Miata Club with Brembo front brakes equipped with 12.88" GWR rotors and Hawk HP+ pads.
Rear brakes are OEM with Hawk HP+ pads.

The last two track days I have experienced pretty significant pulsations from the brakes ONLY after they have been used 4-6 times during a 20 minute session.

I purchased the GWR rotors about 5 months ago. They have about 2500 miles on them including a total of 4 track days.

The first time I noticed the pulsations was at Daytona Speedway. This was before I changed the rear pads from OEM to Hawk HP+.

The second time was recently at Thunderhill on a 5 mile course. This most recent time, the pulsations became so pronounced that I was braking easier than I would have liked to coming into sharp turns after straightaways.

After each track session was completed and the brakes had been cooled down (with e-brake off), the brakes started the next session fine, but the pulsations came back after the brakes heated up every session.

Other than the above two most recent track days and a slight amount of squealing at the end of slow speed road stops (attributed to the Hawk pads), the brakes have performed as expected.

When I mentioned the brake pulsations to others at the recent track day, the response I received was maybe your rotors are warped. I don't see how that can be the cause as the pulsations go away every time after the brakes have cooled - only to return after they have heated up on the track.

I see no visual evidence of cracking or warping of any of the for rotors.

I will also note that the brakes never seemed to be fading (fresh DOT 4 fluid being used), but that the pulsations were so noticeable under hard braking when hot that the car was vibrating, not just the brake pedal.

I'm looking for some guidance (especially from Brian G) related to my problem. I'd also like to know what if any warranty applies to the GWR 12.88" rotors.
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Re: Miata Club w/ 12.88" GWR rotors pulsating on track

Postby Brian » Sun Jun 27, 2021 7:05 am

Rotors don't really warp, what folks are usually talking about with that growing pulsation is a high spot of pad material transfer. It happens when we come to a stop with our foot on the brakes when the rotors were still too hot. Picture is an extreme example, often the transfer is more faint. Having the rotors turned (ground flat) can often get that cleaned off.
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Pad-imprint-on-rotor1.jpg
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Re: Miata Club w/ 12.88" GWR rotors pulsating on track

Postby MichaelE081 » Sun Jun 27, 2021 10:13 pm

Thanks for the feedback Brian. Any suggestions as to how I can avoid this in the future?
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Re: Miata Club w/ 12.88" GWR rotors pulsating on track

Postby Brian » Mon Jun 28, 2021 9:33 am

At track days really use the cool down lap.... with ZERO use of brake pedal and moderate speed with downshifting into the pits and then park car with NO hand brake use at all, just put it in gear on flat ground. Out in the real world if running down a fun canyon the same thing, try to get some good cool down before parking and avoid use of parking brake and put it in gear on flat ground.
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