JRitt@essex

The article in the link below is designed as a roadmap for upgrading the brakes on a modern Porsche 911, based on the environment and manner in which the car is being driven. The primary focus is on the 911 T trim level, as it and the Base 911 come from the factory with the smallest and most primitive brake package Porsche offers. As such, the brakes on Carrera T have the greatest room for improvement. Everything in this article is also applicable to the other 911 trim levels, but the comparative weights and capabilities will be slightly different vs. the stock brake components on those trim levels. The article is loaded with lots of great tech info, comparative weights and measurements, and many of the considerations we all face when using our Porsches on the road and track.
We've helped thousands of Porsche owners with their brakes, and the info in this article is drawn from our experience providing solutions for each of their unique situations. I hope you find it useful, and thanks for reading!

Complete article here: Porsche 911 Brake Upgrade Guide


Below are a few snippets from the article:

Overview of how an HPDE impacts your brake choice:

HPDE (High Performance Drivers Education) / Track Day / Time Trial / Time Attack

At a track day, you will always put more heat into your brake system than you ever will on the street or at an autoX. Please reread that sentence! Track Days are really the first venue mentioned thus far where battling heat becomes paramount for having an effective and reliable brake system. HPDEs typically have a diverse mix of vehicles being run, a wide range of speeds achieved, and vastly differing driver ability across run groups. As such, it's difficult to recommend a single blanket brake solution for a given vehicle driven at an HPDE. We will therefore preface the next portion of our brake recommendations with a brief look at some of the variables encountered at an HPDE or time trial.

After countless discussions with customers on this topic over many years, we believe there are a few critical considerations when upgrading your brakes for a Track Day or Time Attack. These factors will determine just how much thermal capacity your brakes will require:

Track layout

Tire choice

Vehicle modifications

Driving style and experience

A careful examination of these factors in your personal situation will help guide you towards the most appropriate brake solution. Keep in mind that all these factors are related and cannot be considered in isolation from one another.

Track layout

During a brake event, the rotational energy of the spinning discs is converted into heat and spread throughout your discs, pads, caliper pistons, caliper body, and brake fluid (as well as the surrounding suspension components via radiation). The faster the discs are spinning at the initiation of a brake event, the greater the amount of energy converted, and the greater the amount of heat that needs to be dealt with. Therefore, a track with long straights followed by tight turns generates the greatest amount of brake-related heat. The higher your terminal speed at the end of the straight, and the longer you are on the brakes to slow for a turn, the more heat you’ll be pouring into your brake components. When facing a series of long straights followed by tight turns, the issue is compounded even further. The temperature rise on your brake components is both dramatic and rapid during each intense brake event; then the components are immediately doused with cooling air during the subsequent lengthy straight. These rapid temperature swings are what cause the most stress-related brake issues, not necessarily the absolute temperature the brakes reach.

The distance between stops also dictates how much heat is retained in your brakes. If a track layout has a steady succession of medium straights and tight turns (think Carolina Motorsports Park), your brakes might not reach the same max temperature as they would on a track with longer straights, but they won't have much time to cool between stops, creating heat soak. Flowing tracks with long sweepers are much easier on brakes (i.e. Willow Springs or Roebling Road).As noted above, tracks with very long straights followed by tight turns are the most devastating to your brakes (Watkins Glen, Road America, Circuit of the Americas). A close look at the track(s) you'll be regularly driving will help determine just how much stress your brakes will need to endure, how much thermal mass you should seek in your brake discs, and how much fade resistance your pads and fluid will require.

Tire choice

Brakes don’t stop your car, your tires do. Brakes convert the kinetic energy of the spinning discs into heat, but the tires generate friction with the track surface and actually slow the car. Tire choice has a large impact on how much brake your car can leverage, and how much heat will be generated by your brakes. The stickier the tire, the more brake you can leverage, the shorter your stopping distances will be, and the more brake heat you will generate. More grip = more heat. If you're running low grip all-season tires, or if it rains at an event, your tires won't be able to generate as much friction with the track surface, and you therefore won't tax your brakes as much.

Vehicle mass and horsepower

All else held equal, more massive, more powerful cars place a greater strain on their brake system. A Corvette ZR1 will generally require a much larger pad and rotor as a heat sink vs. a Miata. That is partly because of the mass, and partly because of the horsepower. What may surprise you, however, is that the speed component has more impact on your brake requirements than mass does. Higher speeds increase brake demands at an exponential rate, while adding mass increases brake demands at a more linear rate. If you strip 200lbs. out of your car (easier to accelerate), have a quality coilover system (higher cornering speeds), and add 40hp (greater acceleration out of turns), you may be placing less demand on your brakes in terms of vehicle mass, but you'll need to slow the car from higher speeds when entering brake zones. While it may be counterintuitive, the car might be tougher on your brakes despite its reduced weight (Again, outside the scope of this article, but to learn more on this topic, please research the formula K.E. = 1/2 m v2). Again, the relevant point to this discussion is that more massive, more powerful vehicles require larger, more durable brake components, and anything you do to your vehicle to alter its power output or weight will impact your brake requirements.

Driver experience

If you've never driven anywhere but the street, your first couple of trips to the track will most likely not tax your brake system too heavily, right? Not exactly. You being a complete track newb won't necessarily protect your stock brakes from total destruction. Novice drivers may be easier on the brakes for several reasons: Their corner exit speeds are lower, their terminal speeds entering brake zones are therefore lower, and there's less kinetic energy being transferred into heat during a given stop. That said, novice track drivers also tend to stab wildly at the brakes, stay on the brakes far too long, oscillate between on and off brake, and inflict all sorts of brake abuse a pro driver would never do! The result can be some serious brake punishment. It's therefore impossible to make a blanket statement that a novice driver will be fine on stock brake pads. Reality has proven that statement false countless times, particularly on the faster, heavier cars our customers often take to track days.

So where do these factors leave us when upgrading our brakes for a Track Days, HPDE, or Time Trial? The critical point is, every modification you make to your car and the nut behind the wheel will change the demands on your brake system, and you must adjust accordingly. Just because you successfully used a certain pad compound before, doesn't mean it will work again after you've installed bigger turbos and Hoosiers. Chances are that after your 25th HPDE, you'll be taxing your brakes in a different manner than you did during your first event. You'll be hitting higher speeds, entering and exiting corners faster and on a different line, and your car will likely have more grip and power than it did when you started (you'll also likely be much poorer, but happier!). If you typically run Limerock Park (a short track without many big braking zones) but decide to make a trip to Road America (a crazy fast track with huge brake demands), you need to reconsider how your brakes will be taxed. You must constantly evaluate the overall capabilities of your brake system, and not be afraid to try new brake setups as both you and your car evolve.

Finally, if you want to play it safe and not risk damage to the major components of your brake system, don't EVER drive an OEM brake pad on a road course. It may be more convenient and seem economical to run stock pads, but it will eventually cost you time and money in the long run. There's also not much worse than wasted track time. When you're sitting in the pits watching your buddy rip down the front straight, and your stock pads are a steaming pile of dust stuck to the inside of your wheels, you'll be wishing you spent a couple hundred bucks and took the hour on Friday night to change your pads and bleed your brake fluid! Please read this article on the Essex Blog for even more reasons not to run your OEM pads on the track: “Can I Run my OEM Brake Pads on the Track?”

Now that we have a better understanding of how taking our car to the track impacts our brake system, let’s look at track-specific brake upgrades for the Carrera T:

2-piece Discs

Two-piece Brake Discs- Unsprung weight is the devil to the avid autocrosser. You should always be looking to maximize weight reduction within the boundaries of the rules (or outside those boundaries if you’re clever at it!). Weight reduction in the wheels/brakes/suspension area is particularly beneficial to all aspects of acceleration, turning, and braking, which is the core of autoX. Two-piece discs can in some cases offer substantial weight savings. Aftermarket two-piece discs will have aluminum hats that are lighter than the stock iron pieces, and their overall construction and vane design may offer further weight savings. Since you probably won’t be burning your discs up at a rapid rate, the initial cost of a two-piece disc may be worth the weight loss (commonly $600-$1800 per pair). Just make sure to check the price of replacement iron before committing, since you will eventually need to change the discs which are wear items. Also, keep the size and mass of the discs in mind. A larger-than-stock 2-piece disc may weigh more than the OEM units, which is even more likely on the Carrera T since the OEM discs are so tiny.

AP Racing 2-piece J Hook Discs bring numerous benefits to the table that are especially valuable on the racetrack. Taking your discs from 330mm to 350mm in the same 34mm thickness provides an increase in thermal mass, which means you have a larger heat sink to store brake heat. The larger disc diameters spread brake heat over a larger surface area, improving heat radiation. The advanced internal vane design of the AP Racing J Hook pumps considerably more cooling air through the discs, which reduces the amount of heat soak in your brake pads, calipers, and fluid. The AP iron disc metallurgy is more resistant to cracking, and our 350mm discs don’t have any weight penalty vs. stock despite their larger size. The J Hook slot design distributes heat evenly around the disc face and reduces uneven pad transfer, and the J Hook slots are less likely to crack than a drilled hole. The larger J Hooks also look better and fill the wheels up a bit more! These features all converge to ensure that your brake discs will run cooler than your stock discs, have less heat transfer to your other brake components, less propensity to crack, and a offer a considerably longer service life for your discs, pads, and fluid. In summary, there is no downside, yet a whole bunch of upsides to running our 2-piece J Hook Discs on the racetrack.

• Note- A common question we receive is, “If I upgrade to your 2-piece J Hook Discs that mate to my stock calipers, will I later be able to add the AP Racing calipers? ”The answer is unfortunately, “No”. The AP Racing Radi-CAL calipers run on discs of different dimensions vs. the stock calipers. One of the biggest differences is that the radial depth of the AP and OEM discs are considerably different (radial depth is the height of the disc face…the difference between the outer diameter and inner diameter).To learn more about why discs aren’t easily interchangeable, please watch our video, “Will the Brakes From a Different Car Fit my Car? "Again, if you choose 2-piece brake discs to mate with the OEM calipers, and later decide that you want a complete brake kit, you will need to essentially start over and buy the complete brake kit , including the new discs designed to mate with the AP Racing calipers.
• The next logical question then becomes, “Will your 2-piece discs be enough for me, or should I go with a complete brake kit?”That depends completely on your car and how you plan to drive it. Our earlier discussion about modifications, tracks being driven, etc. all factor into how much brake heat capacity you will require. If you plan to stay at stock power, on street tires, running a relatively easy braking track, and you tend not to be terribly hard on brakes, then 2-piece discs may be ample for your needs. If you plan to do a Stage 2 tune, run racing slicks, frequent Watkins Glen, and you tend to be hard on brakes, a complete big brake kit will be a much more appropriate option to provide you the fade resistance and durability you’re likely seeking. If at any time you want more personalized recommendations for your specific needs and situation, we will be happy to guide you through this process based on our prior experience with thousands of Porsche clients.
  • Front AP Racing J Hook Disc Pair for the 991.2 and 992.1 Carrera T
  • Rear AP Racing J Hook Disc Pair for the 991.2 and 992.1 Carrera T

Choosing a disc size

Once you have decided which AP caliper width and finish you prefer, your next choice is disc size. We offer one kit with larger discs, and one with smaller discs. Please note that once you choose a disc size, you cannot later change your disc size. For example, you cannot purchase our rear 365mm kit, and later decide that you want to run our larger rear 380mm discs. The rear calipers have different piston sizes depending on which disc size you choose, and the caliper brackets and disc hats are all completely different in the two kits and are in no way interchangeable. Once you have chosen a kit size, you have no options to change your disc size on the front or rear, so please take your time and choose wisely! Also, the larger front 390mm kit should be paired with our larger rear 380mm kit, and our smaller 372mm front should be paired with our smaller 365mm disc kit. Which disc size you choose should be determined by:

• How much thermal capacity you want/need (based on your modifications, intended tracks, driving style, etc. as discussed above). Our larger 390x36mm discs are considerably more durable than the 372x34mm discs, which are immensely more durable than the OEM 330x34mm discs. The downside to the larger 390mm discs is that they are slightly heavier than the 372mm discs. However, the largest 390x36mm discs still only weigh about the same as the OEM 330x34mm discs, despite the huge size difference!
• What size wheels you plan to run. Our 372mm disc kits can fit inside wheels as small as 18”, but our 390mm disc kits generally won’t fit in anything smaller than a 19” wheel.
• “So, should you go larger or smaller?” If you aren’t worried about shaving every ounce of unsprung weight, you discover that our 390mm discs will fit the wheels you intend to run, you want the greatest durability out of your discs, and plan to add a huge slug of horsepower to your car while driving tracks that punish brakes, choose our larger disc option. If you want to gain considerable thermal mass while still shedding as much unsprung weight as possible, and want to run the smallest, lightest weight wheels possible, our 372mm kit would be your choice.

Some imagery from the article:

99-911

Any options for PCCB equipped cars?

DR911s

Overall, I very much liked the detailed overview and description provided by the OP... but as having spent over 20 years with engineers who design, build, market and service aircraft brakes around the world for all types and sizes of aircraft, both commercial, military and general aviation, using a wide variety of materialsfor the discs and pads including beryllium, special grades of steel, sintered metals, carbon-carbon and carbon-ceramic among them, and as a HPDE participant for over 30 years on a dozen road courses [including VIR, Mid-Ohio, Watkins Glen, Road America and Road Atlanta] on various BMWs with stock and upgraded brakes and 5 years on my 2017 C2S with stock brakes, I disagree with the OP's statement: "Finally, if you want to play it safe and not risk damage to the major components of your brake system, don't EVER drive an OEM brake pad on a road course. It may be more convenient and seem economical to run stock pads, but it will eventually cost you time and money in the long run."

That statement from the OP may be entirely accurate for some people as he mentioned those novices who have very poor braking techniques, but I think his statement is more fitting for "track rats" and especially for those who have modified their cars. I was once a "track rat" but I didn't have the money to upgrade the brakes in the manner described by the OP, although I would have loved such equipment! My view and experience is that Porsche's OEM brakes are have more capacity than most other auto makers, and that Porsche's brake testing standards are severe compared to most automobile makers. Per Excellence magazine, Porsche's testing requires many more back-to-back stops from very high speed for approval. Sorry, but I cannot specifically recall the actual description given in that magazine some time ago, but on my car it would equate to stops from about 160 MPH.

I've had zero issues using OEM brakes and pads at Mid-Ohio and Grattan, running with the advanced group and instructors. But I'm not running Hoosiers or Cup 2s, only Michelin P4S. For certain, I'm not the fastest car on track, but not the slowest either. I don't let the pads wear below 40% remaining and always change the brake fluid before each season, using ATE Type 200.

Fluid and pads are IMO the first items to upgrade for track use. The OEM pads on my car were already semi-metallic type, and perform noticeably better after a warm up lap yet are still quite okay for unexpected sudden stops on the public streets and roadways.

P.S. PCCB discs if used in a multi-disc aircraft brake would be good for one hard stop -- after which they would be welded together due to melting of the unreacted Silicon remaining after manufacture in which silicon is reacted with carbon. That's why present aircraft brakes are carbon-carbon.

JRitt@essex

All our brake kits will fit on cars that were originally equipped with iron or PCCB. The suspension uprights are the same regardless of the OEM brake disc type, so our kit bolts on properly as intended. Our 2-piece J Hook Discs, which are in the OEM sizes, are obviously different depending on the OEM disc type that came on the car.

What year and trim level do you have? If you shoot me a PM I'm happy to provide specific recommendations for your situation/setup. Thanks!

JRitt@essex

Thank you for adding to the discussion! It's always good to hear viewpoints from those who understand the science.

It is true that historically, many European vehicles come with superior brake pads from the factory than many JDM or USDM vehicles. German vehicles in particular have always needed to be competent on the Autobahn, where stops from much higher speeds are required vs. what we see in the USA and other parts of the world. That said, the relentless sequential stops of racetrack use are what tends to cause the most heat-related issues. Even on the Autobahn someone wouldn't typically be stopping consecutively every several seconds for 20-30 minutes at a time.

My recommendations are geared towards the masses after 25 years of watching far too many people destroy their OEM pads on the racetrack (and the brake discs they were run on). For most people, the safe bet is to just not tempt fate with OEM pads. Some people who know what they're doing and understand the ramifications can get away with it (which you obviously do), but for most people they're going to be inviting problems. Novices in particular don't know how to recognize the signals of imminent problems. They don't recognize brake pad fade, uneven pad deposits on their discs, don't understand that they can't run their pads down to the backing plate, etc. In short, the goal of my blanket statement (or gross generalization if you like) in the article is to save those who don't know better from themselves. It's much safer and easier on the wallet in the long-run for most people to just skip running OEM pads on the track. I'm glad you're able to pull it off though, as that is surely the most economical route if you are able to manage the situation!

We supply and service carbon-carbon brake discs in pro racing (IndyCar, IMSA), and I've dealt with Goodrich Aerospace on that material in the past. The big issue with 'carbon' is that most enthusiasts believe that Carbon Ceramic is the same material as the carbon-carbon discs found on racecars. That inference is perpetuated by the OEMs, because they tout carbon ceramic as being 'racing inspired'. The vehicle buyer chooses that option with the understanding that they are the best option for the racetrack, when in fact iron remains the far better option for most people. I wrote another article on carbon ceramic brakes that you might enjoy: Are Carbon Ceramic Brake Discs Better than Iron?
Thanks again for taking the time to provide input.

4 Point 0

Good job Jeff.

Could you talk a bit about swept area (Annulus size) pad size etc.

A couple of guys were chatting and comparing pad sizes. Even though one was getting a better compound, I could not believe how tiny the stock base pads were.

It was only after seeing this i realised why some people were not having good experience with some compounds.

it was because their pad was so tiny on a small annulus.

JRitt@essex

Thanks! That's a great point of discussion 4 point 0, and the source of quite a bit of misunderstanding. I'll try to clarify a few more related points on that topic below.

Swept area is an important factor to consider, and impacts both the pads and the discs. Pad and disc surface/swept area does not directly impact how much brake torque is generated. That is dictated by how far the center line of the caliper pistons is away from the hub, aka the length of the lever arm. As your disc size increases, the caliper is placed further out from the hub, and the amount of torque generated by that longer lever arm increases (increasing the piston sizes in the caliper would also directly increase brake torque). Having more pad area does not inherently create more brake torque. What it does impact is how well the pads and discs can radiate heat. Overall pad volume is the other factor that comes into play, which is overall length, width, height, and thickness. Pad and disc thickness is an important consideration that is often overlooked. Below I will refer to the height of the pad as its radial depth (from the edge that sits on the outside radius of the disc (OD) to the edge that sits at the inner edge of the disc (ID)). This is commonly expressed in millimeters. On the pad image below, the radial depth would be the distance highlighted by the red arrow.






In racing, we tend to use pads and discs that have a relatively shorter/smaller radial depth. That doesn't mean that the surface area of the pad is small. A larger surface area is gained through a longer pad, which is accommodated by a six piston caliper. There is no inherent benefit of a six piston caliper vs. a four piston caliper. In some ways, a four piston caliper is actually superior. Because it has two fewer pistons it is less complex, has fewer moving parts, is less expensive to rebuild because it has fewer piston seals and fewer pistons, etc. A four piston can even be stiffer because it is a shorter rectangle and more box-like/square in structure. However, a four piston caliper's main weakness when used on the front of a car is that it can typically only accommodate a relatively smaller pad vs. a six piston caliper. That is why racecars almost exclusively use six piston calipers on the front. The larger caliper allows for a longer pad, which increases both surface area to radiate heat, while also increasing the pad's overall volume as a heat sink. The next logical question then is, why not use an 8 or 10 piston caliper and make the pad even longer? Once the caliper becomes too long, it becomes more flexible and loses stiffness. When a pad becomes too long, it starts to run into taper wear problems along it's length and the leading and trailing edges of the pads start to wear unevenly. Therefore, the pad size for the typical six piston has shaken out as the happy medium over the years, offering the best blend of stiffness, resistance to taper, and adequate volume for heat radiation and storage.

Another goal in racing is weight reduction. All else held constant, a disc with an extremely tall radial depth tends to be far heavier than one with a shorter radial depth. There's simply more iron mass present. While removing some of that mass and reducing the radial depth of the disc does reduce it's capability as a heat sink, other features are added to improve its ability to shed heat. For example, curved or wave-shaped internal vanes are used to increase airflow and cooling. Therefore a racing disc tends to have a shorter radial depth than the OEM Porsche pads and discs. For example, our front AP Racing by Essex brake kits use a pad and disc with a radial depth of 54mm. The typical OEM front Porsche pads have a radial depth somewhere in the 62-67mm range. However, a racing pad tends to be thicker, which increases the pad's ability to store heat. The pads in our front six piston calipers are either 18 or 25mm thick, whereas most of the stock Porsche pads tend to be 16.6mm in thickness. Another reason racing brake systems strive to be more compact is for wheel fitment. For many years were were cramming as much brake as humanly possible inside 15" NASCAR Cup wheels. To gain more heat capacity, everything got wider since it couldn't be any larger in diameter.

In summary, the pads in a racing brake system tend to be shorter, longer, and thicker than those on a road car. The pad swept area is increased by adding length to the pads via a six piston caliper, and the pad volume/heat capacity is increased by making the pads thicker. Because they have a shorter radial depth, the discs in a racing brake system are lighter than those typically employed in road brake systems Their internal vane structure is superior to a road disc, as it flows more air and cools more readily through convection. OEM discs tend to not flow nearly as much cooling air, and they instead rely more on radiation. This is how a properly designed racing brake system can be more efficient and effective than a road system that has considerably larger discs, so it's not just as simple as saying, "That brake system will take more track abuse because the discs are bigger."

Another great tool for helping understand these concepts is to look at the PCCB vs. the iron factory brake systems on a given 911 model. The PCCB discs are almost always larger. Why? Because carbon ceramic discs rely on radiation to a great extent for cooling, rather than convection. The carbon ceramic discs can't be formed with the complex internal vane structure of an iron disc, and therefore can't flow as much cooling air. All else held equal, a carbon ceramic disc will also run considerably hotter than an equivalently-sized iron disc. The carbon ceramic discs therefore need a larger surface area to radiate heat into the air surrounding the brakes. That means we almost always see a carbon ceramic disc that is larger in diameter, and usually taller in radial depth as well.

To give you an idea of the relative pad thicknesses I mentioned above, below are the two pad thicknesses we offer in our front six piston calipers. The pad on the left is 18mm, and is similar to what most people who haven't seen professional-level racing brake systems are familiar with. The pad on the right is the one that goes in the front AP Racing CP9669 calipers we use on Porsches. It is 25mm thick. In pro racing, some of the pads we use are 30mm, nearly twice as thick as a common road pad!




This image of the 25mm thick pads from our CP9669 AP calipers provides some scale. They tend to last a VERY long time and dramatically reduce the frequency of pad changes.

4 Point 0

Awesome. Loads of great info in that.

I originally had the lighter, shallower radial depth, setup like race cars have, however I kept cooking calipers. Race cars have huge cooling. Ducts that compensate for the less thermal efficient setup.

I have since changed to a Hi Thermal setup, with a mono-block caliper with vented pistons.

Whats the effect of having a much stiffer caliper and vented pistons?


Brembo GTS

Brembo GT-R

Hi thermal rotors