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I posted something similar over at Rennlist and think I’ve figured out what I want to do but I also wanted to get thoughts from the 981 community specifically.

981 2.7, 18” wheels. Started doing DEs last year, love it and want to do a bunch more. Stock pads performed great for me, but I went through them pretty quickly so I’m going to run track pads this year. I’m going to install caliper studs to make changing pads easier/less risky and that’s where I ran into the question of rotors: my stock drilled rotors seem fine now, but they’re going to crack/wear too thin eventually. The slotted rotor selection for 981s isn’t all that huge, so I was thinking of switching to Girodisc (or something else) up front at some point. But they’re bigger than stock, so if I installed studs now that worked with my stock rotors I would need to replace them with longer studs if/when I switch to a larger rotor to avoid dealing with the problems of drilled rotors.

So my questions are: is it worth it to go with standard length studs now with the likihood of having to replace them with longer studs later, in terms of the effort/potential problems from removing them once they’re locktited (is that a word?) in place? Regardless of when I do it, is there any problem with running larger rotors just up front or even with larger rotors front and rear? I wouldn’t think it would cause an ABS issue but it would be good to get some insight from you guys with more experience with this. Also, will the 350mm rotors from Girodisc fit under my stock 18” wheels or will it be a tight enough fit that it might be a problem?

I’m not trying to build a track car, just get away from a couple of problems that I think are likely to come up as I start to spend more time doing this. I’m not trying to avoid spending money so I don’t mind doing things up front that I’d have to do eventually even if I won’t see the benefits right away, but I’m also not trying to throw it away so I’m just trying to do what makes sense.
 

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No, you can't just add larger front rotors. That will throw off the front to rear brake bias. If you go Giro, you need both front and rear rotors at the same.

If you are getting into DEs, I would strongly suggest the brake upgrade. What is the most important part of your car when you are going 100+ mph into a 40 mph corner. Stock parts are ok, but I would put my first money into brake upgrades to stay even safer. They work better, run cooler, fade much less, last longer, and are less likely to fail or have a problem due to their higher capacity to stop the car.

Caliper bolts definitely add convenience for pad changes and also safety by reducing the wear on the aluminum upright that they bolt into. Not sure how taking out the old ones will affect that aluminum upright. I would just call Ira at Target Engineering and explain your situation. He might be able to recommend a stud length that could work for your stock calipers and one that could also work for the larger Giro Disc rotors and their spacers. The difference will be 10mm more for the Giro setup. I just ordered 85 mm studs for my PCCB calipers.
 

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350mm brakes fit fine under 18" wheels. Some 18" wheels, like the Apex wheels, will take a 380mm brake.

I run a Brembo GT 6 piston 355mm kit on my 987 and will likely go bigger once my Apex wheels arrive. :)

I wouldn't worry about caliper studs until you know what route you're going to go. I've changed lots of pads without any issues.
 

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No, you can't just add larger front rotors. That will throw off the front to rear brake bias. If you go Giro, you need both front and rear rotors at the same.

If you are getting into DEs, I would strongly suggest the brake upgrade. What is the most important part of your car when you are going 100+ mph into a 40 mph corner. Stock parts are ok, but I would put my first money into brake upgrades to stay even safer. They work better, run cooler, fade much less, last longer, and are less likely to fail or have a problem due to their higher capacity to stop the car.

Caliper bolts definitely add convenience for pad changes and also safety by reducing the wear on the aluminum upright that they bolt into. Not sure how taking out the old ones will affect that aluminum upright. I would just call Ira at Target Engineering and explain your situation. He might be able to recommend a stud length that could work for your stock calipers and one that could also work for the larger Giro Disc rotors and their spacers. The difference will be 10mm more for the Giro setup. I just ordered 85 mm studs for my PCCB calipers.
Hey Lovetoturn,

I thought 350 mm Girodisc rotors were close, if not the same, to stock rotors except they have removable hats and are not drilled. If that is the case I think you can run 350 mm Girodisc rotors on front and stock rotors on the rear as long as the calipers are compatible.

Am I wrong?
 

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AP911,
Physically, you can indeed put Girodiscs on front and keep the stock in back. BUT, ... Girodiscs for the 981 are designed to be used with and include spacers to hold the calipers further (10mm?) away from the hub than stock. That changes the leverage of the caliper and therefore increases its stopping power. Imagine that you want to torque a bolt with a short wrench vs long wrench. Applying the same pressure (which is what the 981 will do) to the longer wrench will put more torque into the bolt than with the short wrench. So it's not the rotors that change the bias, it's the spacers. And you can't use these rotors without the spacers since the stock calipers will not fit over them otherwise. If you put Girodiscs on the front, you'll need to put them on the rear as well to keep the same brake bias. That said, you can certainly take your chances with an altered bias.
B
 

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Well said, except I would never take chances with my brakes. When you add the rear calipers they have spacers too and that balances everything out as far as the brake torque is concerned. Venders make complete kits for a reason. Again you have to do both axles to get a balanced brake system. Makes no sense to get BIGGER brakes on the front alone that will actually make the car's braking capacity and balance much worse.

I upgraded to PCCB calipers all around, but then Porsche changes the size of the brake pistons to rebalance the torque between the front and rear axles considering that there are now 350 mm rotors in both the front and rear.
 

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Stock 981 brake hardware is total overkill unless you are running 275/315 slicks in endurance racing, so for DEs there is no need for hardware changes. You can do it if you simply want the bling but it won't affect your stopping power or stopping distance in a measurable way.

Match the brakes to your chosen tire patch. If you are running R-comp tires get REAL racing brake pads like RS-29 or Raybestos ST-43, slotted rotors, and hi temp fluid like Motul 600. I also added 981 Cup cooling ducts to the front. 50 track days on this car now and ZERO brake issues ever. My front pads are also good for 20+ track days which is unheard of.
 

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Well I have giant OEM GT3 Pads on my 350 mm Giro disc with 6 piston PCCB calipers and they are worn out after only about 12 days. These pads have over 50% more surface area than stock and still wear out in less than a year. So everyone does not have the same demands placed on their brakes depending on which tracks you visit and how you drive. The difference between beginner, novice, intermediate, advanced, and instructor level driving places varying loads on a car's braking systems.

Fluid, pads, and a different duct are a good start and may work for some, but not for everyone.

That is a good start initially, but as your driving level advances you may want to add per say a Giro Disc upgrade to larger rotors to increase your heat tolerance and resistance to fade. These rotors go from 330 to 350 in front and 298 to 325 in the rear. Many have complained about the rears getting too hot from an over anxious PSM and this upgrade helps alleviate that problem as well as not getting premature "brownbos".

The next step can be what I did with the OEM PCCB calipers and thicker 350 mm discs all around. This is basically a factory option from Porsche for the 981, but with steel instead of carbon rotors. In his well massaged Cayman S, JCviggens is running within a mile or two per hour of the top speed of the GT4s at his track, and Porsche sees fit to put 380 mm rotors on that car. So if you are running a modified Cayman with almost 370 hp and are an advanced driver, then brakes with 350 mm rotors is about safety and longevity of the equipment and not bling.

For reference, when a pad is 60% worn, I consider it as done when going to the track. You need that last 40% of the pad as insulation from heat to protect the pistons from passing the heat into the brake fluid, boiling it, and causing fade or worse consequences.

Everyone is entitled to there own opinions, and these are just mine. Maybe they are worth two cents or maybe they help keep someone from having a brake failure some day. I recently read about a GT3 guy on Rennlist that had a major off when he had a catastrophic brake failure due to a caliper bolt coming out of the front left upright. The caliper ripped off and destroying that whole corner. Consequently he only had brakes on the front right and left rear to stop the car. He is thankful to still be here today. I now have caliper studs on my car like all the Cup cars do. Maybe that is overkill, but I don't want to be the next guy telling a story about his close call with almost meeting his maker.
 

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Great points up there! ^^

Caliper studs are SUPER important on models which have CLOSED calipers - ie ones where you HAVE to unbolt the caliper to change the pads
Rears go through hell....PSM activation when turned off creates a ton of heat...check your rear calipers for the brownish color tinge. Larger REARS do indeed assist with this greatly.
 

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For reference, when a pad is 60% worn, I consider it as done when going to the track. You need that last 40% of the pad as insulation from heat to protect the pistons from passing the heat into the brake fluid, boiling it, and causing fade or worse consequences.
Had not thought about that, but it makes sense.

I have a GT4 and am amazed at how long stock pads last. I will stay with those until there is a compelling reason to change. Right now the braking power seems fine to me.

One of my sons has a Fiat Abarth and we put a big brake kit just on the front. I was wondering if there would be any front-to-rear brake balance issues, but it seems fine. I'm not suggesting that experience translates to Porsche, but its a data point. BTW: the rear rotors are so small on the Fiat, we almost considered not hooking them up and keeping the cool, 100% black look the new (stock-sized) rotors came in. :)
 

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Well said, except I would never take chances with my brakes. When you add the rear calipers they have spacers too and that balances everything out as far as the brake torque is concerned. Venders make complete kits for a reason. Again you have to do both axles to get a balanced brake system. Makes no sense to get BIGGER brakes on the front alone that will actually make the car's braking capacity and balance much worse.

I upgraded to PCCB calipers all around, but then Porsche changes the size of the brake pistons to rebalance the torque between the front and rear axles considering that there are now 350 mm rotors in both the front and rear.
lovetoturn - Were the PCCB calipers a direct bolt-on or did they require additional hardware other than the 350mm Girodiscs? I have seen elsewhere that the PCCB part numbers for our 981s are:
  • 991-351-426-34 (FR Caliper)
  • 991-351-425-34 (FL Caliper)
  • 996-352-424-32 (RR Caliper)
  • 996-352-423-32 (RL Caliper)
  • 999-067-053-09 X8 (Caliper Bolts)
​Thx
 

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Sorry, have not been on this forum for a while. The stock PCCB calipers for the 981 of course fit right on to the car without additional hardware and the 350 Giro discs are a direct replacement for those rotors. Just simple plug and play. Three plus years now, and no problems. Without checking, I would assume you did your homework and those are in fact the correct numbers for the parts. They just come out of the Porsche computer. Good luck with your upgrades.
 
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