Over the weekend, I de-installed the Relentless 2-piece brake rotor kit at all four corners. Switched to Z1 motorsports relatively cheap, good quality 1-piece slotted OEM replacements:
Akebono 370Z/G37 Sport Package Performance Rotors.
I don't want to get into a big vendor bash side-debate here. Let's just say the scientific data from my end is inconclusive on whether any quality problems in the RA rotors themselves contributed to my issues. I don't think RA has sold enough 370Z rotors in total for anyone to make any statistical argument about the quality level, either, so it's a crapshoot from that perspective. Let's just say in the end the total package of their business model, product, and pricing isn't matching up well with my needs. A good deal of that has to do with their turnaround time on shipping out parts, too.
I'm not planning to re-install the RA rotors. If someone else wants to buy the re-usable aluminum hats and rear caliper upgrade hardware to try out the system themselves, they could buy a fresh set of RA's outer rings to go with them. The fronts
are 10 lbs unsprung/rotating weight lighter per rotor than OEM equivalents, so there is that going for them. Otherwise I'll see if RA wants to buy them back as inventory (no flaws with those bits for sure), but that seems unlikely, or just junk them and write off the cost as a lesson learned.
In any case, I've re-bedded on the new Z1 rotors, and everything's much healthier now. I re-used the XP8's I already had for rear pads since they have tons of life on them and the rear RA rings were still in good shape when I took them off. In the front I was concerned the pads were degraded from spending a couple months mating with the front RA rings, and I wanted to upgrade heat ranges anyways, so that's bedded with a fresh set of XP10s. I might clean up and resurface the takeoff front XP8's since they have a lot of thickness left, and keep them as backup front pads to take to the track with me.
XP10+XP8 feels pretty good, the front bite's not as scary as I was worried it would be, it's fine with street tires and still easy to modulate. 6 days to back on the track again at MSR Houston. Need to re-bleed again after a couple more days of working the system out, and get an oil change in, and I'm good to go.
Being paranoid about wasting any further track weekends on unexpected brake issues, I was extremely analytical and careful with the new rotor installations. I took dial-gauge runout reading on all 4 rotors and thickness variation data, etc, and did some indexing of the mounting rotation offset to minimize the runout. Everything's way way below OEM spec limits. My worst corner is at .004" runout prior to bedding measured all the way out at the edge, and even that I think was reduced slightly with the wheel torqued on top (as opposed to lightly torquing lugnuts onto the brake rotor itself when measuring). The OEM spec limit is .014" a bit in from the edge (center of pad swept area, basically). So, measurably, these are good rotors in manufacturing quality terms.