That's hard for me to understand. My stock 996 tt rotor was 330mm and the Brembo GT replacement was 355mm. It would seem that the 12.5mm difference in the arm of the 2 rotors would provide increased torque with the 355. How can this give the same brake torque as the stock system? When I added the 355mm 997 rotors to the rear, the maximum g-force with the same tires was increased. Perhaps the rear brakes were never going to the point where ABS for the rear tires was triggered. I understand that any system that takes all 4 wheels to ABS level will provide the same g-forces no matter what diameter rotor or swept area of pad but it seemed to me that my system was biased to the front when I installed the GT kit for front only.

 

Because there is more at play than disc size. See the previous post on the equation for brake torque. You are neglecting the piston area. We size the pistons on the calipers to maintain the braking torque as close as possible to stock.

 

Well I've been running the 997TT rear rotor with the 996TT rear caliper, and the 997GT3 caliper/350MM 997TT rotor combo for a long time now, both on the street and at the track with ZERO negative effects.

This combo is well known to work well and I'm not the only one using it with great success. When I spoke with several indy shops about upgrades and known imcompatibility issues (specifically brake bias), NONE (including one sr. tech for Flying Lizard) had a single negative thing to say about the upgrade or issues with brake bias.

15 days out of a set of rear pagid yellows and phenominal performance (as many here have seen first hand by my car on track) are all I have to go on, and all I need.

Mike

 

It doesn't seem like people are reading the posts.

The issue is with 997TT calipers and discs on the rear of a 996TT. The slight increase from the stock 330mm disc to the 350mm 997TT disc would not significantly impact the overall brake balance. The big impact is with the large pistons of the 997TT calipers not with the disc size increase.

That said, I can't really recommend the 996TT calipers with a 350mm disc because the disc path in that caliper was designed around a 330mm disc, and when used with a larger one the clearance between the edges of the caliper and the disc is too small. I guess no one is experiencing any problems though.

 

I agree with Mike. My system has also worked better than the stock system with no problems or complaints. Wonder why Brembo is chiming in considering they make all the components being discussed. Of course some of their systems would make them more money than others.

 

Actually read the posts and you'll see why I'm chiming in. It is a safety issue. I am not trying to sell anything here.

All I've done is provided accurate information. It is up to you what you choose to do with it.

 

No, I understood clearly... What's a little confusing is why when I specifically asked about the 997TT SYSTEM, I was told there would be no issues. I also don't believe that the 997TT caliper/piston/bore differences would be significant enough to cause the scenarios you're describing. We're talking using the 997TT Rear caliper/rotor in conjunction with the front 997TT caliper/rotor , correct?

What is the bore size on the master difference between the 996? and 997TT?

As to the comment about the spacing difference between the 996TT caliper and 330mm rotor and the 997TT rotor, I measured that and made sure I had enough area clearance because I was concerned with any chance of heat soak with the caliper being to close to the rotor edge. No issues at all...

Mike

 

The rear 997TT calipers should not be used on the 996. Even when used with the 997TT front system or a Brembo GT system. Like I said the 997TT rear caliper and disc combination increases the rear brake torque by 48%. That is an enormous change.

Who did you ask about the 997TT system? Someone that actually knows the underlying physics and what the parameters are? As it stands, you've got an outstanding and inexpensive system on your car. The 997TT front components along with the 350mm disc and 996TT caliper on the back maintains the optimum balance while increasing the fade resistance, and extending brake pad life.

It is not just a matter of the master cylinder, it is the brake proportioning and ABS system that is of concern as well.

Unfortunately, it isn't feasible for me to teach a seminar on complete brake system design here on the forum. I design brake systems for a living, and if individuals don't believe that I know what I'm talking about then by all means disregard my suggestions. I am not doing this out of self interest, I am not trying to sell brake systems. I just want to point out that there can be significant consequences to bolting on parts that, though they may fit, are not appropriate.

 

It's not a matter of "not believing you". It's a matter of understanding WHY... nothing more. You've actually saved me some money, since I was planning to upgrade to those calipers to match my 997TT rear rotors.


Mike

 

Hopefully I've explained why now, but sometime when I think something is clear it really isn't.

I am going to write up a lengthy description of brake system design and post it later. Most will probably find it extremely boring, but some might find it useful. Stay tuned.

 

Mark, I apologize for not reading all your posts. What you say makes a lot of sense. I'm going to talk to the guys here and what we're going to do is pull our new rear brake kit and just offer the rear 997T rotors as an add-on to the 6-piston front kit.

I really appreciate your knowledge on this subject, it definitely comes from years of experience that not many other people out there would have!

 

Wow, good information. There are many other vendors selling these 997TT/GT3 rear calipers and recommending them as a safe and effective addition to the 6 piston Porsche fronts... I spoke in length to 2-3 before making my purchase... I would love to hear other opinions on this topic from some of the other brake experts out there.

Mark-your input and data is much appreciated! Thank you for chiming in here!

Mark-what are the specs on the 996GT3 rear calipers? How different are they than the 996TT rears? Other vendors and tuners sell the complete 996GT3 setup, front and rear, for use on the 996TT's... I have been told that the front calipers are the same for the 996 GT3's and the 997TT and GT3's so it would be interesting to see what the 996GT3 rears are set like? Are there other differences in the 996GT3 master cylinders, brake proportioning setup, etc...?

 

Tom Kerr-aren't you running the Brembo 6 pot fronts (aftermarket) and 997TT rear calipers for aggressive track use? Thoughts/input?

 

Steve-would you then be making and selling relocator brackets so that the bigger rotors will work? This is not a direct bolt on... The guys like Mikelly and Al Norton who have used the 350mm rear rotors both fabbed up relocator brackets...

 

I'm looking into it right now. For the time being we've taken down the rear kit and just have the front kit available.