Upgrading the WRX brakes with StopTech

After almost a quarter million miles of neglect and abuse on our WRX, it was time we started upgrading the Subaru WRX brakes.   The brakes on Ian’s trusty WRX have seen better days.  We chose StopTech as the best big brake kit for the WRX.  Replacing all the brake hardware with an upgraded 4 wheel system that is nothing short of fantastic, especially when compared to the stock system.

StopTech Big Brake Kit upgrade for the WRX.

We have always felt that the base WRX is a great little car that punches above its weight class.  Its potential has always been overshadowed by the presence of its big brother the STI.  The WRX brakes are an example of this. The STI gets much better brakes from the factory, decently sized Brembos while WRX languishes with smallish two-piston floating caliper front and single piston floating rear calipers with small rotors and amazingly, a small and solid non-vented rear rotor!  If any car can benefit from a StopTech brake upgrade kit its a base GD WRX.

Ian noted to us that when he was younger and used to do canyon runs and drive more aggressively, that his brakes would fade at an alarming rate to the point of being scary.  Well with our planned track intentions with grippier tires and more power with our planned engine rebuild, this was going to have to change.  Help give us the best WRX brake upgrade, StopTech!


ST40 4-piston fixed caliper with a 328mm vented Aerorotor

The StopTech brake kit for WRX – 83.836.4300.53 starts by upgrading the WRX brake system with front ST40 4-piston fixed caliper and a 328mm vented rotor.  We opted for StopTech street performance pads since our new brakes are so much larger than stock.  The StopTech BBK also has a DOT approved braided steel brake line.

Included in the WRX brake upgrade kit is the StopTech Aerorotor is a two piece part with an alloy center hat. This saves a lot of weight as the center of the stock rotor is a chunk of cast iron. The rotor’s iron alloy has been selected for its coefficient of friction and wear-resisting properties over a wide range of temperatures. The rotor has radial slots on the friction faces to evacuate gas from vaporizing pad material during high-speed applications to improve bite and to have consistent braking at high temperatures.


The Aerorotor is 28mm thick, much thicker than the stock rotor and has generous vents that are flow optimized using CFD analysis.


The rotor is mounted to the hat using shouldered bolts that allows the rotor to move about 0.012″ back and forth independently from the hat. By allowing the friction ring part of the rotor to float freely, it will not distort with heat. One-piece iron rotors tend to warp into a cone shape when hot since the center section of the rotor acts as a heat sink and causes differential heating of the friction face with resulting differential expansion. This causes uneven pad contact, inconsistent braking force, poor pedal feel and inconsistent wear. Floating the rotor also makes the brake system more forgiving to caliper piston knockback caused by play in the wheel hub’s bearing system. Knockback can cause a long pedal after the wheels experience side loading. The rotor hat contacts the friction ring of the rotor on vaned pillars machined into the hat.  This reduces heat transfer to the wheel hubs by allowing cooling airflow to be pumped between the hat and rotor. Conical inconel washees put a sight amount of preload on the rotor preventing it from rattling on the hat.


  1. You are spoiled with your dry California weather. it looks easy when everything still has factory paint. Trying to do this and the suspension bushings on a similar car here in the northeast would involve torches, penetrating oil, and lots of strong language.

  2. I need a press, lathe and mill… And as DedBull noted, less rust! Sweet upgrade, fingers crossed it will last a long time for you.

  3. Will you be tracking this car? I did 20 track days on an ’04 WRX and found the pad knockback on stock brakes and street tires substantial. A larger diameter rotor will mean larger deflections and more knockback. I was considering going BBK but then the pad knockback plus tracking a car with 60% of the weight in front made me realize it would be cheaper and more fun to do the E36 M3 route. I only miss the WRX on the track when it rains.

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