996 NA vs 996 TT Brakes for Narrow Body Turbo Carrera

[polizei]

Hey Guys,

I've crunched the numbers on going with 996 NA or 996 TT brakes via Steve Timmons on my '87 Turbo Carrera, and both are doable. I'd just like to get your input on which to go with.

My car is running 375 HP now, but I'd ultimately like to be between 450-475 long term. It will be primarily used for hi perf street , but I would like to do 1 or 2 track days per year. One of the factors to consider is that I've got a narrow body Carrera w/ 17" rims. After chatting with Bill Verburg, it sounds like, without getting too extreme, the best size tires to run are 225/45 up front and 255/40 in the rear.

I know that for street use the 996 TT brakes are definitely overkill. I'm wondering if my skinnier tires would be better matched with the 996 NA brakes? Obviously I'd be saving on weight with the 996 NA brakes, and I'd have less brake bias. Whereas, with the 996 TT brakes, I'd have better heat distribution. But by comparison, if I wasn't at or approaching the heat capacity of the 996 NA rotors, would there be an advantage in terms of stopping power with the 996 TT brakes?

Consider the case of two cars with identical brakes. One car has skinny tires and the other has wide tires. Since the braking distance of the car with skinny tires is longer than the car with wide tires, would more heat be produced in the rotors of the car with skinnier tires? If so, the car with skinny tires would reach the thermal capacity of its rotors sooner than the car with wide tires. What I'm getting at is, on a track day, can you effectively compensate for the braking distance of skinnier tires with bigger brakes? I'm sure this isn't the best example.

Thoughts?

[Bill Verburg]

Originally Posted by polizei

Hey Guys,

I've crunched the numbers on going with 996 NA or 996 TT brakes via Steve Timmons on my '87 Turbo Carrera, and both are doable. I'd just like to get your input on which to go with.

My car is running 375 HP now, but I'd ultimately like to be between 450-475 long term. It will be primarily used for hi perf street , but I would like to do 1 or 2 track days per year. One of the factors to consider is that I've got a narrow body Carrera w/ 17" rims. After chatting with Bill Verburg, it sounds like, without getting too extreme, the best size tires to run are 225/45 up front and 255/40 in the rear.

I know that for street use the 996 TT brakes are definitely overkill. I'm wondering if my skinnier tires would be better matched with the 996 NA brakes? Obviously I'd be saving on weight with the 996 NA brakes, and I'd have less brake bias. Whereas, with the 996 TT brakes, I'd have better heat distribution. But by comparison, if I wasn't at or approaching the heat capacity of the 996 NA rotors, would there be an advantage in terms of stopping power with the 996 TT brakes?

Consider the case of two cars with identical brakes. One car has skinny tires and the other has wide tires. Since the braking distance of the car with skinny tires is longer than the car with wide tires, would more heat be produced in the rotors of the car with skinnier tires? If so, the car with skinny tires would reach the thermal capacity of its rotors sooner than the car with wide tires. What I'm getting at is, on a track day, can you effectively compensate for the braking distance of skinnier tires with bigger brakes? I'm sure this isn't the best example.

Thoughts?

W/ my track 993 w/ full RS brakes there is no issue at all w/ 225/40x18 tires, the car stops. Of course it helps that there is R rubber. On the street car which also has 993RS brakes and 225/45x17 tires again, no problem you just never get into them any where near like what you do on track. I closely monitor rotor temps and could easily go down a size in rotors if temp was the only criteria to go by

If it were my car I'd go 996, and use fresh SRF or Motul fluid and track pads for track days

[polizei]

Bill, thanks for your continued feedback. From your experience, if all other factors are held constant, do the 996 TT brakes have an advantage over the 996 NA brakes in terms of stopping distance? Also, are there any circumstances under which you'd recommend going with with the 996 TT brakes over the 996 NA brakes for a narrow body Carrera?

I know I'm probably splitting hairs here, but when I think about spending around $3k on something, I like to know that I'm making the best choice! Thank you!

[Bill Verburg]

Originally Posted by polizei

Bill, thanks for your continued feedback. From your experience, if all other factors are held constant, do the 996 TT brakes have an advantage over the 996 NA brakes in terms of stopping distance? Also, are there any circumstances under which you'd recommend going with with the 996 TT brakes over the 996 NA brakes for a narrow body Carrera?

I know I'm probably splitting hairs here, but when I think about spending around $3k on something, I like to know that I'm making the best choice! Thank you!

996tt
330x34 & 330x28 have more thermal mass and are capable of generating somewhat more brake torque than the 996, which are 318x28 & 299x24.

for comparison 993RS are 322x32 & 322x28, 930 are 304x32 & 309x28

my main quibble w/ 996tt is that they have more front bias than I like to see, whenever I check rotor temps the fronts are always way hotter(>2xs) the rears. Again for comparison purposes the 993RS are roughly the same f/r, I'm getting the back to take a lot of the load off the front. 996 are more like the older 911 setups in terms of the bias temps seen

In my run groups I regularly monitor 993RS, 911, 997tt, 997, 996, Cayman S and 996tt rotor temps so get a good feel for comparable usage from the different setups

the 996 and Cayman S are the same setups and handle track loads well, they do run hotter than 996tt or 993RS or 930 and will need better fluid and pads

[175K911]

I have the 996TT brakes with Timmins hardware on my '86. My car is strictly a track car. But as Bill has said many times, these brakes are heavily biased toward the front. When I ran 225/45-17 R888 on the front, I could lock the front tires at virtually any speed. Too much front brake and not enough tire. But the upside is that I got through 22 track days last year on the same set of Hawk pads.

For the street, I think you'd be better off for a number of reasons:
Less front bias
Less unsprung weight with the slightly smaller rotors. The TT stock rotors are uber heavy
Potentially better wheel clearance depending on what 3 piece wheels you plan to run. I need 5mm spacers on the front of mine.

That being said, I have never come close to overheating my brakes or fluid at the track. But I can barely get them hot on the street.

[ChkbookMechanic]

Like 175K911 I have the 996tt brake kit on my car and also like his, mine is purely track. The brakes are biased a bit more toward the front than I'd like, but upgrading to a dual master cylinder will fix that problem (so would different brake pads for front and rear).

I run the Fikse FM10 wheels and require about a 1/4" spacer up front to clear the calipers.

[Flieger]

Tire width is not necessarily related to the stopping power. It is the total grip- whether from compound, tread pattern, diameter or width.

The car with less total grip (you said narrower tires) will not be able to stop as fast as a car with more grip (wide tires). If the initial speed and weight are held constant, that means that the car with wide tires has more deceleration. Now, Force =Mass x Acceleration. Where you get into heat is with the amount of Work. Work is the integral of Force with regard to distance. If you have significantly more Force but a little less distance, then there will be more Work done and more heat. So, even though the change in momentum of the car is the same, doing it quicker means more heat.

So, you are actually stressing the brakes less with narrow tires so there is no extra heat to compensate for.

[spuggy]

Originally Posted by Bill Verburg

my main quibble w/ 996tt is that they have more front bias than I like to see, whenever I check rotor temps the fronts are always way hotter(>2xs) the rears. Again for comparison purposes the 993RS are roughly the same f/r, I'm getting the back to take a lot of the load off the front. 996 are more like the older 911 setups in terms of the bias temps seen

Bill, could you expound slightly on that? Do you mean that the 996 temperature differences front/rear are similar to 911 setups? Not clear how that compares to 993RS?

Out of interest, would you be kind enough to provide a few "typical" sets of front/rear temperature values just for ballpark?

On my Timmins 996 conversion, I used Pagid Yellows front and Black (RS14) rear, rationalizing that this gave a "better" front/rear bias when both sets of pads were cold, and the fronts would heat faster/more than the rears, giving slightly more CoF (and thus front bias) under heavy braking - this seems to have worked out very well, as the car feels very balanced and just seems to hunker down evenly (but slightly more at the front) under hard braking.

I was very leery of ending up with too much front bias (e.g. 996TT) after reading an online review of an aftermarket (non-Porsche) brake conversion that delivered worse braking performance 60-0 than stock - because the rears weren't contributing enough.

[mnmasotto]

Bill if you come out to Southern California I would love to buy you dinner and a 18 y.o. Single Malt Scotch. Lets say Macallan 18 y.o. What do you say?
Mark

[polizei]

Originally Posted by Bill Verburg

the 996 and Cayman S are the same setups

Bill, does this mean the 996 NA and Cayman S brakes would require the same front and rear adapters for use on a 3.2 Carrera?

[Bill Verburg]

Originally Posted by polizei

Bill, does this mean the 996 NA and Cayman S brakes would require the same front and rear adapters for use on a 3.2 Carrera?

yes, they are the same parts,

[Bill Verburg]

Originally Posted by spuggy

Bill, could you expound slightly on that? Do you mean that the 996 temperature differences front/rear are similar to 911 setups? Not clear how that compares to 993RS?

Out of interest, would you be kind enough to provide a few "typical" sets of front/rear temperature values just for ballpark?

On my Timmins 996 conversion, I used Pagid Yellows front and Black (RS14) rear, rationalizing that this gave a "better" front/rear bias when both sets of pads were cold, and the fronts would heat faster/more than the rears, giving slightly more CoF (and thus front bias) under heavy braking - this seems to have worked out very well, as the car feels very balanced and just seems to hunker down evenly (but slightly more at the front) under hard braking.

I was very leery of ending up with too much front bias (e.g. 996TT) after reading an online review of an aftermarket (non-Porsche) brake conversion that delivered worse braking performance 60-0 than stock - because the rears weren't contributing enough.

here are some relevant hyd. bias ratios
993RS 1.472
996/Cayman S 1.72
996t/997S 1.919
911 '69-83 1.596
930 1.604
these #s are the basis for what you get in the car, some are modified a bit by differences in f/r rotor diameter some are not, bias is shifted to the end w/ bigger diameter rotors
993RS/996t/997S use exactly the same rotor diameter f/r, 996/Cayman S use ~6% larger diameter fronts, 911 uses ~2.8% bigger rears, 930 uses ~1.6% bigger rotors in back.

to use 993RS type bias the car has to be setup for it, very stiff, very low, very effective trailing throttle lsd but it is fantastic at shifting the braking work load to the back of the car, this is reflected by the drastically lower rotor temps hence, pad and rotor life seen on a 993RS when it's tracked,

here are some typical rotor temps taken ~10min after parking in the paddock
993RS 450/400 Pagid yellow
911 475/385 PFC
996 785/370 pagid yellow/pagid black
997S 785/435 pagid yellow/pagid black
911SC 510/425 pfc/pagid black
911SC 485/435 pfc/pfc

these are not actual operating temps and were not collected in any scientific manor, just a quick spot check at roughly the same time after use from the same run group(except the SCs)

[spuggy]

[QUOTE=Bill Verburg;5541225here are some relevant hyd. bias ratios
993RS 1.472
996/Cayman S 1.72
996t/997S 1.919
911 '69-83 1.596
930 1.604
these #s are the basis for what you get in the car, some are modified a bit by differences in f/r rotor diameter some are not, bias is shifted to the end w/ bigger diameter rotors
993RS/996t/997S use exactly the same rotor diameter f/r, 996/Cayman S use ~6% larger diameter fronts, 911 uses ~2.8% bigger rears, 930 uses ~1.6% bigger rotors in back.[/quote]

The reasons you cite are why I'm calculating/using the figures for braking torque at each axle - as you clearly know, hydraulic ratio only shows part of the picture as it doesn't factor in rotor diameter, pad height (point of application of the torque being the mid-point of the swept area) and the coefficient of friction of the pad material.

I was initially surprised by the larger-than-(I)-expected differences caused by relatively small variances of pad CoF - according to my calculations, Pagid Yellow front and Pagid Black rear gets a 996 setup pretty close to the "golden" 1.6:1 front/rear bias ratio - if you're calculating torque.

That's with cold pads, so I wanted an idea of how much more the front might/would heat up when used in anger(!)

Initial "seat of the pants" testing is extremely positive, but it's hard to get them hot on the street for obvious reasons

Originally Posted by Bill Verburg

here are some typical rotor temps taken ~10min after parking in the paddock
993RS 450/400 Pagid yellow
911 475/385 PFC
996 785/370 pagid yellow/pagid black
997S 785/435 pagid yellow/pagid black
911SC 510/425 pfc/pagid black
911SC 485/435 pfc/pfc

these are not actual operating temps and were not collected in any scientific manor, just a quick spot check at roughly the same time after use from the same run group(except the SCs)

Understood. Just wanted a "ballpark" idea of difference front/rear - this is great info, thanks!

[polizei]

I'm moving forward with the brake conversion over the coming the weeks. I'll be working with Steve Timmins of InstantG's Home Page to install 996 NA brakes on my '87 Carrera. Steve will be providing the calipers, and we'll be installing new Zimmerman rotors on all 4 wheels.

Any recommendation on brake pads? I'll be driving mostly on the street with 1 or 2 track days per year. I'd ideally like something that's versatile enough that I don't have to swap pads on the occasional race day. I'm not looking to break any records (or the bank). I'm just looking for something that will pair well with my new calipers/rotors.