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I was doing some research for my dad who was running out of thermal capacity on his 350/350 setup on long sessions during open lapping days.
The 991.2 Turbo 380x34mm rotors will work with the OEM S/GTS Calipers with the use of extended Studs and Spacers.
I used 95mm Studs w/ sleeves with a 14mm spacer on the upper mount and 18mm spacer on lower mount. I would maybe buy the 105mm studs next time tho.
Hopefully the 380/350mm setup will have enough thermal capacity.
The radial depth and sweep area is correct, as the 991.2 Turbo uses the same Pad shape as the S/GTS cars. I didn’t put new pads in when I swapped last night, but pad surface and sweep area will even out after some bedding.
The radial depth and sweep area is correct, as the 991.2 Turbo uses the same Pad shape as the S/GTS cars. I didn’t put new pads in when I swapped last night, but pad surface and sweep area will even out after some bedding.
Interesting that a larger rotor would use the same pad as one of a smaller rotor.
I wonder if there would be GiroDisc options for anyone who desires bigger rotors.
Interesting that a larger rotor would use the same pad as one of a smaller rotor.
I wonder if there would be GiroDisc options for anyone who desires bigger rotors.
You can use any 991.2 Turbo 380x34mm rotor from girodisc, PFC, AP or whomever else for this. I just didn’t want to buy an expensive disc for this experiment.
Photos of spacers and close ups as requested. I will note that the 14/18mm spacer stagger will cause the caliper to not sit 100% flush, but when torqued down, I feel the thousands’ gap (I used a feeler gauge) is within acceptable range.
Bedded the pads, feels good. No abnormalities to report.
The inside radius of ring isn’t making full contact yet, but I’m guessing it will as the pads wear in a little more.
I’d personally have no issues tracking this setup tomorrow.
I will note that the 14/18mm spacer stagger will cause the caliper to not sit 100% flush, but when torqued down, I feel the thousands’ gap (I used a feeler gauge) is within acceptable range!
@DC021
I went back into this thread and didn’t see an explanation as to why you used a different spacer for the top vs the bottom. I would think you would want a 16-17mm spacers for BOTH to accommodate the larger rotor. (Considering a 30 mm increase diameter from 350-380, then go slightly more than half that. That’s like using 11-12mm spacers when increasing rear rotors from 330 to 350mm). Am I misunderstanding something?
@DC021
I went back into this thread and didn’t see an explanation as to why you used a different spacer for the top vs the bottom. I would think you would want a 16-17mm spacers for BOTH to accommodate the larger rotor. (Considering a 30 mm increase diameter from 350-380, then go slightly more than half that. That’s like using 11-12mm spacers when increasing rear rotors from 330 to 350mm). Am I misunderstanding something?
It’s because the caliper isn’t mounted centrally on the wheel bearing / axle axis.
It’s because the caliper isn’t mounted centrally on the wheel bearing / axle axis.
I don't understand this. If the caliper is mounted at some angle, wouldn't you maintain that angle as you slide it away from the center point, thus requiring equal size spacers? In your first "after" pic, it looks like the edge of the brake pad is at an angle relative to the circumference of the inside of the brake rotor friction surface. I checked my 2018 GTS and there is no angle. The pad tracks that inner circumference. How do you explain that?
You’re welcome to try yourself! Just sharing what I had to do to make it work 😁.
At first I too wanted to use 14mm on both, but had to add an additional spacer on the bottom.
OK, I’m not physicist or engineer but not sure why you would have started with 14 when a 380mm rotor extends 15mm further out ag any given point vs a 350mm rotor. At least that’s what it would seem to me thinking very simplistically. Therefore, If I were experimenting with this, I would have started with at least a 16mm spacer for both top and bottom. This is not to be critical of your work here. I appreciate what you’re trying to do and like where this is going.
Last edited by Tier1Terrier; Oct 13, 2024 at 10:26 AM.
OK, I’m not physicist or engineer but not sure why you would have started with 14 when a 380mm rotor extends 15mm further out ag any given point vs a 350mm rotor. At least that’s what it would seem to me thinking very simplistically. Therefore, If I were experimenting with this, I would have started with at least a 16mm spacer for both top and bottom. This is not to be critical of your work here. I appreciate what you’re trying to do and like where this is going.
Well as the engineer here, I again will again say that the caliper isn’t mounted centrally on the wheel’s axis. This photo from Racing Brake’s 380mm conversion kit kinda shows what I’m on about. Notice how they too, have to stagger their stack height?
Well as the engineer here, I again will again say that the caliper isn’t mounted centrally on the wheel’s axis. This photo from Racing Brake’s 380mm conversion kit kinda shows what I’m on about. Notice how they too, have to stagger their stack height?
OK, I see it now - thank you for posting this. The further from the center, the more the caliper's alignment approaches perpendicular to the normal line defined by the rotor's center. Thus, you have to slowly adjust the caliper's angle. Now it makes sense.
Your brake pad is definitely angled a bit though ... not sure if that is any concern in practice.
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380mm Front Rotors on S/GTS
