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A Brake Upgrade path for the Subaru WRX and STI
May 27, 2021
If you are looking to improve your cars braking performance, the place to start is with a better set of brake pads and a higher temperature fluid.You can definitely make a noticeable improvement to your cars stopping ability this way, but if you are tracking your car, putting on much larger wheels and tires, and especially if you are running R-Compound race tires, you may not be able to get enough improvement out of pads and fluid alone.
The next step from here is to look at putting on an up-graded caliper, of a full big-brake kit that uses larger rotors and calipers to give you a big step up in your stopping ability.
There are a lot of options out there for this, so we wanted to put together a blog that helps to walk you through the common options for your WRX or STI.
Subaru 4-Pot and 2-Pot calipers
These calipers first came on the Version 6 STI in Japan, but they also came on the 2006 - 2007 WRX as well. The front calipers use the same size rotor that the WRX has had from 2002 - 2014, so they are a simple up-grade, and the rear rotors are ventilated and slightly larger than the standard 02 - 05 WRX so on that car especially, the set of front and rear Subaru 4-pot and 2-pot calipers can be a very good, cost effective up-grade.
These calipers are also awesome for gravel and rally use because they will fit under 15" Rally wheels.We have been using them on our Rally car for years, and they are quite common on Subaru Rally cars.
For 2002 - 2005 WRX
These calipers will work with your stock front rotors, so if they are in good shape, you don't even need new rotors to put on these calipers.
In the rear, you will need the KNS V1 adapter to bolt the caliper to your knuckle, and you will also need the 2006 - 2007 rear rotors (they are 290mm) to work with these calipers.
For 2004 - 2007 STI
You can run these calipers, but keep in mind that they are smaller than the STI Brembo's, so you would typically only do for Rally Applications. The calipers will be a direct bolt on ( you will need WRX bolts because they are a different thread than the bolts for the Brembo's), but you will need different rotors front and rear.
If you have a 2004 STI only, you will need WRX front and 2006 - 2007 WRX rear rotors (both of which are 5x100 bolt pattern).
If you have a 2005 - 2007 STI, you will need the KNS gravel rotors which are 5x114.3 rotors.
2008 - 2014 WRX
The Front Subaru 4-Pot calipers are still a direct bolt-on for the front brakes, but the rear Subaru 2-pots will require a different bracket (the KNS-007) and a different rotor to work.
To fit the caliper you will need the BRZ rear rotors because they are wider and vented, and have the correct sized drum for the parking brake for the 08-14 WRX. It is also recommended to switch to the 2006 - 2007 WRX style rear brake lines.
Because of the relatively small size of the factory rear caliper and pad, the Subaru 2-pot rear caliper is a good starting point for a brake up-grade on this car. However, if you need a big improvement in stopping power, and you are looking to up-grade the front brakes as well, the STI Brembo calipers would be a great option. We will get to the details further down the post, but the black STI Brembo rear calipers are a very simple bolt on for the 08-14 WRX, and they make a much bigger difference compared to the Subaru 2-pot calipers.
2008 - 2014 STI
For the 2008-2014 STI, the install of the Subaru 4-Pot and 2-Pot calipers is largely the same as on the 04-07 STI. In the rear you will need the KNS-007 bracket with the FHI/Subaru hardware, and for both the front and rear rotors, you will need a special "Gravel" rotor to fit with the 5x114.3 hubs.
Because this is a smaller brake and rotor package, for this car we would only recommend these brakes for Rally applications where you have to fit 15" wheels on the car.
It is also recommended to switch to the 2006 - 2007 WRX style rear brake lines.
2004 - 2017 STI Brembo Brakes
From 2004 - 2017, the STI came with front and rear Brembo brakes which gave the STI great brake performance, and the good news is that these can be fitted to a WRX of a similar year range fairly simply.
From 2004 - 2007 the STI had gold calipers, and from 2008 - 2014 the STI had black calipers. The front calipers are identical except for the color, but rear calipers are actually fairly different. Because of the difference in the calipers, the Gold rears can be fitted to the 2002 - 2007 WRX and the 2008 - 2014 WRX with the correct bracket(The KNS-007). The Black rear calipers can only be fitted to the 2008 - 2014 WRX, and they do not require any bracket for installation.
The front STI Brembo calipers attach to the front knuckle with the same mounting points as all of the years of the WRX (2002 - 2014), so the only thing that you need to install them are Brembo bolts (they are a different thread pitch than the WRX calipers), and STI rotors that will work with your WRX hubs.
Brembo front caliper bolts:
2004+ STI Front caliper bolt Click Here!
2004 - 2007 STI Rear caliper bolt Click Here!
2008 - 2014 STI Rear caliper bolt Click Here!
Where is this up-grade ideal?
STI Brembos are a fantastic up-grade for any WRX to give you much improved brake performance on the street. They will also give you much better performance on track, but because they are street calipers, they are not ideal for dedicated or aggressive track use. They do have external dust seals, so if you are going to be tracking a high power car, or using an aggressive track pad compound, you will want to keep an eye on these seals, and if you have issues with melting them, etc., we would recommend a more track focused brake up-grade.
For 2002 - 2005 WRX
Up front, you only need the STI bolts and rotors to install the front calipers.
In the rear, you will need an adapter bracket (KNS-005) with Brembo hardware, and for the rotor, you will either need an adapter rotor to work with the smaller R160 parking brake, or you will need the KNS-800 adapter shoes that will let you use a standard 2004 - 2007 STI rear rotor.
Click Here for the KNS-800 Adapter Shoes for the WRX
For 2006 - 2007 WRX
Same install up front as the 2002 - 2005 WRX.
In the rear, you can bolt the gold Brembo calipers to your existing brackets, you will only need the corresponding Brembo bolts (the thread pitch is different). For rotors, you have the same two choices as the 2002 - 2005 WRX with either an adapter rotor, or the KNS-800 adapter shoes to run a standard 2004 - 2007 STI rear rotor.
2008 - 2014 WRX
Up front, the install is the same as the previous years of WRX. You just need Brembo bolts to attach the calipers to your WRX knuckles, and rotors to match.
In the rear, because it attaches with a smaller bolt spacing, you can run the Gold STI Brembos, but you will need the KNS-007 bracket with Brembo hardware. For rear rotors, you will just need a 2008 - 2014 STI rear rotor with 5x100 bolt spacing.
Click Here for the Black Brembo Front Calipers
Click Here for the Black Brembo Rear Calipers
For this year range of WRX, the Black Brembo calipers are more ideal because the rear calipers will bolt to your WRX mounting bracket with Brembo hardware.
AP Racing 325mm Competition Brake Kit with CP8350 AP Racing Calipers
Don't let their size fool you. Even though this AP Racing brake kit uses calipers and rotors that are the same size as the STI Brembo calipers, this kit offers superior on-track performance compared to the STI Brembos. The key difference here the calipers and pads.
The AP Racing CP8350 calipers use a pad that is twice as thick as the Brembo pad, and this has a few benefits. The most obvious is longer pad life (and believe it or not, these pads cost about 40% less than the Brembo pads with the same compound), but they also isolate the caliper from heat much more effectively than the Brembo pads as well.
In addition, the AP Racing calipers do not have any external dust seals, so they are much better suited to aggressive use, and the heat that track pads will create than the STI Brembo calipers.
This kit also comes with two-piece AP Racing J-Hook rotors which are a substantial weight savings over the stock STI rotors.
All in all, this kit offers much better on-track performance than the STI Brembo's do. And because the less expensive and longer lasting pads, this kit can honestly pay for itself over a couple of seasons of use. For very high power cars, or race cars that are using 275 width or wider R-Compound tires, you may be better suited to a larger competition brake kit. Just keep in mind that they will require 18" wheels to clear the larger rotors and calipers.
2018+ STI 6-Piston Brembo Calipers (and STI Type RA Calipers)
Starting with the STI Type RA, and then the 2018+ STI, Subaru finally gave the STI a brake up-grade with larger Brembo calipers, with a 6-piston Brembo caliper up front. The front calipers use a 340mm rotor, and the rear calipers use a 328mm rotor. Because of the larger rotors, this can be an up-grade for the previous generations of STI.
Up front, the attachment of the front calipers is still the same as the black and gold Brembo calipers, so as long as you have a 340mm rotor that will work with your STI or WRX hub, these calipers are a direct bolt on.
The rear caliper and rotor are entirely different than the previous generation of STI, and as of writing this, we only know that they are a direct bolt on for some of the 2015+ WRX's, and we don't know if they can be adapted to fit on the older WRX's or STI's.
Where is this up-grade ideal?
Because these Brembo calipers still have the external dust seals, and because of the weight of the front rotors (they are even heavier than the 328mm STI rotors), this is a more ideal up-grade for a street car than a car that is seeing a lot of track use. There is also a somewhat limited availability of the front (and especially the rear) pads in terms of compound currently. So for full track use, a different brake kit with lighter components and better pad selection might be better.
As a quick note on wheel fitment, we have test fit all of the factory STI wheels (18" or larger) back to 2008 and they all clear these 6-piston front calipers.
Brembo 355mm GT Front Brake Kit
Brembo has had a 6-Piston brake kit for the STI for a number of years, and even though it looks very similar to the 2018+ STI Brembo caliper, there are some key differences. The first being that this kit uses a 15mm larger rotor (355mm versus 340mm) 2-piece rotor. This larger rotor weighs a good deal less than the 340mm STI rotor, and it gives the caliper a better mechanical advantage because of its larger diameter.
The calipers themselves are one-piece calipers which are more rigid than the 2-piece STI calipers, and they also run a much larger brake pad. This caliper has been around for a long time, so there is currently a better pad selection for this caliper compared to the STI 6-piston.
One thing to note is that with any of the Brembo mono-block calipers, you must remove the caliper from its mounting bracket to change the pads because they cannot be removed through the top of the caliper.
Where is this up-grade ideal?
This kit will offer better brake performance because of the larger rotor, which is also lighter in weight, compared to the 2018+ STI Brembos. They do still have external dust seals, but they do seem to have a fairly high heat tolerance. Scotty ran these brakes on his STI race car for a number of seasons, and didn't have any issues with them needing to be replaced. This brake kit would be an ideal up-grade for street performance, and moderate track use. If you have a dedicated track car, a more motorsports oriented caliper would be a better long term option.
Roger Clark/Alcon 365mm front 343mm rear brake kit
Roger Clark Alcon 365mm Front Brake Kit
Roger Clark Alcon 343mm Rear Brake Kit
For all-out Motorsport use, Roger Clark Motorsport worked with Alcon to develop a 365mm front and 343mm brake kit that offers exceptional braking performance. The Alcon calipers do not have external seals, and they use thicker pads (18mm thick pads up front for instance) similar to the AP Racing calipers. This gives you long pad live, better heat management, and light weight braking performance.
Because these kits use Alcon calipers, motorsports oriented pads are fairly available, depending on the manufacturer. Street pads are available as well, but this kit is more designed around track use.
Where is this up-grade ideal?
Roger Clark Motorsports has adapted these kits for all of the WRX and STI models from 2002 up to 2014, and this kit is an ideal motorsports option for any car in that range. We are currently running the 365mm front kit on our Pikes Peak race car, and it provides massive stopping power very consistently for us. The light weight design is a fantastic feature as well as the thicker pads, etc. This kit is ideal for aggressive track use, and for high power WRX's and STI's.
Brembo Club Sport 350mm x 34mm Front Brake Kit
This is the brake kit that Scotty up-graded to from the standard Brembo 355mm GT kit.
The Brembo Club Sport kits are designed around motorsport use, and so they use large calipers without external seals, very thick pads (some kits can fit 25mm thick pads), and thicker rotors as well. These brake kits are designed around aggressive track use or endurance racing, and they are designed to provide massive stopping power from high speeds, or over long track sessions. This is a great option if you are going to be running in a 20+ minute track session wheel to wheel where you need consistent stopping for the entire race, or if you are running any kind of endurance event where you will be on track for long periods of time.
They are ideal for any form of endurance racing, especially in a higher power car.
Essex Designed AP Racing Radi-CAL Enduro Brake Kit - Front CP9660 (04+ STI)
The AP Racing Radi-CAL Competition Brake Kit for the STI is designed to give you maximum stopping power and control, no matter if you are running in a short sprint race, up to a full Endurance event where you will be on track for hours at a time.
This kit uses a 355mm x 32mm 72 vane AP Racing Disk, and the AP Racing CP9668 Radi-CAL 6-piston calipers. These calipers use a 25mm thick (per side) pad, and the calipers themselves are designed to be as light as possible, while also being incredibly rigid. As an added benefit, the material removed from the calipers also helps to improve the cooling for the brakes.
If you need the ultimate stopping power for your WRX or STI, the AP Racing Radi-CAL is a fantastic choice.
If you would like more information about picking brake pads, we have put together a blog with information about that as well. Here is a link to that:
We also just put up episode 86 of the Flatirons Syndicate Motorsports Podcast with Ken from KNS brakes, and it is a great conversation about brakes from pads and rotors up to looking for a Big Brake Kit. It is a great conversation that may also be helpful and the link to that is below:
Thanks for reading!
-Jon Cooley
