View Poll Results: I want a big red brake kit for my Carrera T!?!
Hell yeah, with a nice group discount.
55
74.32%
Nah, the stock brakes are good enough for me.
19
25.68%
Voters: 74. You may not vote on this poll
Hey Suncoast, how about a Carrera T big brake package deal?
06-03-2018, 01:07 AM
#46
Burning Brakes
06-03-2018, 03:30 AM
#48
Drifting
Beautiful 991. 
50th Anniversary model?
50th Anniversary model? 
06-03-2018, 07:15 AM
#50
Rennlist Member
For the price of an otherwise identically spec'ed S you can buy a T plus add carbon ceramics and ecu flash...
06-03-2018, 01:20 PM
#53
Burning Brakes
On the 991.1, the stock rotor sizes were:330 x 28330 x 28340 x 34330 x 28
On the 991.2, they are:330 x 34330 x 28350 x 34330 x 28So, the while the rear brakes are identical on all of the cars, the fronts are thicker on the base 991.2 and 10mm larger in diameter on the 991.2 S. Going to the Girodisc rotors on the base car will get you to the S rotor size with the 4-piston calipers. This should provide a small increase in front brake fade resistance, where it is likely needed.
Even with no track aspirations, I plan to make this change, when my 991.2 C2 needs front brake rotors.
On the 991.2, they are:330 x 34330 x 28350 x 34330 x 28So, the while the rear brakes are identical on all of the cars, the fronts are thicker on the base 991.2 and 10mm larger in diameter on the 991.2 S. Going to the Girodisc rotors on the base car will get you to the S rotor size with the 4-piston calipers. This should provide a small increase in front brake fade resistance, where it is likely needed.
Even with no track aspirations, I plan to make this change, when my 991.2 C2 needs front brake rotors.
06-03-2018, 01:23 PM
#54
Burning Brakes
On the 991.1, the stock rotor sizes were:
330 x 28 330 x 28
340 x 34 330 x 28
On the 991.2, they are:
330 x 34 330 x 28
350 x 34 330 x 28
So, the while the rear brakes are identical on all of the cars, the fronts are thicker on the base 991.2 and 10mm larger in diameter on the 991.2 S. Going to the Girodisc rotors on the base car will get you to the S rotor size with the 4-piston calipers. This should provide a small increase in front brake fade resistance, where it is likely needed.
Even with no track aspirations, I plan to make this change, when my 991.2 C2 needs front brake rotors.
330 x 28 330 x 28
340 x 34 330 x 28
On the 991.2, they are:
330 x 34 330 x 28
350 x 34 330 x 28
So, the while the rear brakes are identical on all of the cars, the fronts are thicker on the base 991.2 and 10mm larger in diameter on the 991.2 S. Going to the Girodisc rotors on the base car will get you to the S rotor size with the 4-piston calipers. This should provide a small increase in front brake fade resistance, where it is likely needed.
Even with no track aspirations, I plan to make this change, when my 991.2 C2 needs front brake rotors.
06-03-2018, 02:51 PM
#55
With same calipers on larger rotors, one supposes that the leverage of those pads might go up—but their work, too...without them getting "stronger." Then again, new front calipers with piston sizing that is a compromise might be a bigger problem. Would be curious to hear PeteVB weigh in on this. But I will say: The Baer brake upgrade I did on my XR4Ti years ago was front only and transformed the car's braking performance.
Older cars often do well with more front brake bias if you’re mounting modern sticky tires on them. The stickier the tire the more weight transfers forwards, so they’ll often do well with a front only upgrade. Modern cars are pretty well dialed I from the factory and use a more sophisticated pressure balancing system, so my strong preference is to keep the brake torque and pressure near stock. Once you start changing pad friction you can get unintended consequences (strange behavior when cold, etc).
06-04-2018, 04:32 PM
#56
But on to the brakes, I am open to it but honestly I want to see how the base ones feel first. I don't care about looks so much on a GR car.
Last edited by uhn2000; 06-04-2018 at 05:39 PM.
06-04-2018, 05:48 PM
#57
Rennlist Member
Brake math is generally pretty straightforward. Moving the caliper out by using it on a larger rotor increases its mechanical advantage and increases front brake toque proportionally. Measure from the centerline of the caliper pistons to calculate the change. To bring the brakes back into balance you can (in order of preference) use a caliper with less total piston area, change the brake bias valve (or master cylinder) or use a brake pad with a lower coefficient of friction. I’ve done each of these on different cars with decent results.
Older cars often do well with more front brake bias if you’re mounting modern sticky tires on them. The stickier the tire the more weight transfers forwards, so they’ll often do well with a front only upgrade. Modern cars are pretty well dialed I from the factory and use a more sophisticated pressure balancing system, so my strong preference is to keep the brake torque and pressure near stock. Once you start changing pad friction you can get unintended consequences (strange behavior when cold, etc).
All makes sense, and has me thinking that keeping the calipers and pads while increasing the front and rear rotor size (in such a way to preserve the balance) would be preferable for the 991.2 Carrera. May be easier said than done. Fwiw, a recent run on the loop with a T on the standard brakes surprised me: They were up to the task. I suspect the Tenerife car had pads that weren't bedded in...kinda like a 718 GTS here in CA two weeks ago. Maybe the margin for bedded//not bedded is thinner with the turbo engines. Still looking into it.
06-04-2018, 06:47 PM
#58
Rennlist Member
Thread Starter
Thanks, Pete.
All makes sense, and has me thinking that keeping the calipers and pads while increasing the front and rear rotor size (in such a way to preserve the balance) would be preferable for the 991.2 Carrera. May be easier said than done. Fwiw, a recent run on the loop with a T on the standard brakes surprised me: They were up to the task. I suspect the Tenerife car had pads that weren't bedded in...kinda like a 718 GTS here in CA two weeks ago. Maybe the margin for bedded//not bedded is thinner with the turbo engines. Still looking into it.
All makes sense, and has me thinking that keeping the calipers and pads while increasing the front and rear rotor size (in such a way to preserve the balance) would be preferable for the 991.2 Carrera. May be easier said than done. Fwiw, a recent run on the loop with a T on the standard brakes surprised me: They were up to the task. I suspect the Tenerife car had pads that weren't bedded in...kinda like a 718 GTS here in CA two weeks ago. Maybe the margin for bedded//not bedded is thinner with the turbo engines. Still looking into it.
That's exactly what girodisc is doing, increasing both front and rear rotor sizes and keeping the proportioning the same. That's why I like this idea so much!
06-04-2018, 06:55 PM
#59
Burning Brakes
Brake math is generally pretty straightforward. Moving the caliper out by using it on a larger rotor increases its mechanical advantage and increases front brake toque proportionally. Measure from the centerline of the caliper pistons to calculate the change. To bring the brakes back into balance you can (in order of preference) use a caliper with less total piston area, change the brake bias valve (or master cylinder) or use a brake pad with a lower coefficient of friction. I’ve done each of these on different cars with decent results.
Older cars often do well with more front brake bias if you’re mounting modern sticky tires on them. The stickier the tire the more weight transfers forwards, so they’ll often do well with a front only upgrade. Modern cars are pretty well dialed I from the factory and use a more sophisticated pressure balancing system, so my strong preference is to keep the brake torque and pressure near stock. Once you start changing pad friction you can get unintended consequences (strange behavior when cold, etc).
I haven't examined the brake pads in a 991.2, but I would guess that they are about 2 inches wide. If so, with the 330mm rotor on the base Carrera/Carrera T, that would suggest a working radius of about140mm, or 5.5 inches. Going up to a 350mm rotor with the calipers spaced outward by 10mm would increase that radius to about 150mm or 5.9 inches. That's about a 7 percent increase, which doesn't strike me as too much.
Moreover, these cars have ABS, so any small disturbance to the brake balance would still not lead to any undesirable front or rear lockup.
Last edited by Valvefloat991; 06-04-2018 at 06:56 PM. Reason: grammar
06-04-2018, 10:17 PM
#60
Sorry to join in but was enjoying the read. I just cooked my brake fluid in my 991.2 GTS. I have the 6 Pots up front and 4 pots in the rear. Its not enough. As no one has mentioned how to get some nice improvements I will here.
1. Get Braided/Steel lines
2. Up grade your brake fluid to at least a 600, or if heavy track use Castrol SRF. (Its expensive per litre, but you don't need much.)
3. Next is a pad up grade
4. Then a rotor upgrade
5. If you are still not happy with any of those, you will need a full BBK.
I am wondering if I can use 380 GT3 rotors and pads with my GTS 6 pots?
1. Get Braided/Steel lines
2. Up grade your brake fluid to at least a 600, or if heavy track use Castrol SRF. (Its expensive per litre, but you don't need much.)
3. Next is a pad up grade
4. Then a rotor upgrade
5. If you are still not happy with any of those, you will need a full BBK.
I am wondering if I can use 380 GT3 rotors and pads with my GTS 6 pots?