Running 380/380 F/R rotor setup

[patroklai]

Hey guys question,

In doing research on BBK, I found that those who ran the 380/380 often times sold or even flat out traded their kit for smaller rotors.

While I think a big driver for the change was likely running smaller diameter 18 wheels for the track or square setups, I'm curious what the experiences were with those who ran or are currently running a larger rotor in the rear. From what I've seen, the larger diameter rotor helps with cooling but did not have a direct effect on brake bias as the caliper and number/overall piston size remain unchanged. It seems (for example), Brembo will use the same caliper on a 355 or 380 rotor with the difference being the bracket.

Can anyone share their experiences or perspectives on 380/380 setup? Thanks.

[pbonsalb]

I don’t think there is any reason for 380mm rears. Extra weight. No issues with overheating smaller rotors. Relatively little braking power comes from the rear. With any of the well known BBK front and rear kits for these cars, the rears calipers are smaller 4 piston units because no more is needed, regardless of the # of pistons up front.

380mm front rotors with Stoptech ST60 fit under 18” ARC8 and some other 18s. Other brands have bulkier 6 piston calipers and may not fit with 380 or even 372mm rotors.

[roastbeef]

correct, size is less relevant than people think. check out these brakes and scroll down to read what goes into these brakes and compare to other brake offerings. you'll find some of the features are unparalleled.
https://www.essexparts.com/ap-racing...93-m3-1m-coupe

[Redd]

I think people change out their 380 kits to fit 18" wheels for track. That's the only reason I can think of.

I have a Brembo GT 380/345 setup. It's a mismatched kit which I found used, but IMHO is the perfect setup. 380 up front, and smaller lighter 345 in the rear. No issues so far, love them. I've got 5-yrs 65k kms in them and only used 1mm of disc wear. And that's with occasional track days and high performance Project Mu HC+ pads.

[patroklai]

Thanks all. Is there a point of diminishing returns? Stock rear is 350. Is anything above 355 or so a waste?

[roastbeef]

Originally Posted by patroklai

Thanks all. Is there a point of diminishing returns? Stock rear is 350. Is anything above 355 or so a waste?

yes.

[patroklai]

Originally Posted by roastbeef

yes.

Thanks!

[Captain Caveman]

The diameter of the rotor DOES have an impact on brake torque, as a larger disc will increase the mean radius (centre of disc to centre of pad). A larger rotor will lead to a greater brake bias, and smaller rotor the inverse.

[pbonsalb]

Which is why the front brakes should be matched to the rears and are matched with any kit designed for these cars whether it is a front kit or front and rear kit, regardless of the number of pistons and rotor size. In other words, this should not be an issue unless you are making your own kit without paying attention to the things you should be considering.

[wyatth]

The 380s are overkill but there is nothing inherently wrong with that or them. They are Brembo's primary kit for this car and was designed as a kit to get the torque bias as intended. You can get the same rear BBK performance with less weight in another option (although the rears are thinner (28mm) than the fronts (34mm) so they actually don't weigh much more than stock). But yes, the primary reason people move on from 380s is to fit more 18'' wheels, shed more weight, etc.
E92 GTS (378/380!), M2 CS (380/370), 991 GT3 (380/380), etc all run Brembo kits much closer to 380/380 from the factory, albeit they also have different weight distributions. So a lot goes into it, otherwise why not just make a 355 kit with the same torque (playing with piston sizes) and save more weight?
I got a good deal on my 380 kit and am very happy with them. Sure lighter would be cooler, and at times I've been tempted by BBS RIAs which do not clear 380s, but ultimately am happy with the ZCP wheels and these brakes which look, work, and feel fantastic all the time.

* I’ll add that it’s not so different from the ST60 fronts. Bigger and heavier than the ST40s, which by all accounts are dequate for this car even on the track. But the ST60s remain popular (partly because the ST60 380 is slightly smaller than the Brembo 380, so fits a few more 18” options).

[patroklai]

Originally Posted by wyatth

The 380s are overkill but there is nothing inherently wrong with that or them. They are Brembo's primary kit for this car and was designed as a kit to get the torque bias as intended. You can get the same rear BBK performance with less weight in another option (although the rears are thinner (28mm) than the fronts (34mm) so they actually don't weigh much more than stock). But yes, the primary reason people move on from 380s is to fit more 18'' wheels, shed more weight, etc.
E92 GTS (378/380!), M2 CS (380/370), 991 GT3 (380/380), etc all run Brembo kits much closer to 380/380 from the factory, albeit they also have different weight distributions. So a lot goes into it, otherwise why not just make a 355 kit with the same torque (playing with piston sizes) and save more weight?
I got a good deal on my 380 kit and am very happy with them. Sure lighter would be cooler, and at times I've been tempted by BBS RIAs which do not clear 380s, but ultimately am happy with the ZCP wheels and these brakes which look, work, and feel fantastic all the time.

Great feedback buddy. Thank you.

[wyatth]

You’re welcome! I’ve also considered going down to the 365 kit, but the calipers (pistons) are different as well to control torque/bias. It’d be a complete trade at that point and just not worth it to me. If I could just get new rotors and brackets/pads, maybe I would.

[patroklai]

Originally Posted by wyatth

You’re welcome! I’ve also considered going down to the 365 kit, but the calipers (pistons) are different as well to control torque/bias. It’d be a complete trade at that point and just not worth it to me. If I could just get new rotors and brackets/pads, maybe I would.

I thought the rear caliper was the same for 380mm. Isn't it the 4 piston or do the piston sizes change based on rotor size?

[wyatth]

Fair point! I actually don't know if the rear calipers vary when the rotors step down from 380 to 345. I do know the front calipers are resized when the rotors step down from 380 to 365, and assumed the rear would as well (but could be wrong). But the fronts alone being different is enough to conclude it's not just a matter of new rotors for me.

I'd love a 365/345 Brembo GTS kit!


Another thing I've noticed with 365/345 kits is that the drilled rotors do not match F/R. By that I mean the drills in the front and rear rotors are noticeably different (the rear drills look bigger, more like 380 drills, while the 365s have small drills like ceramics). On the 380 kit, the rotors all look the same, as expected. I do not know what to make of this, if anything. Non issue on slotted rotors (which I run now). But, enough to trigger my OCD if I was set on drilled rotors for some reason.

[patroklai]

Haha I'm OCD too. Would make me crazy.