Project Subaru WRX STi Part 4: Brake System Upgrades


If a larger brake rotor is installed the effects of knockback are greatly magnified and the brakes are more sensitive to any sort of run out in the hub bearings.  Since the STi is blessed with the equivalent of a racing brake upgrade stock, we decided to work around the stock rotor size to help reduce the effects of knockback.  This involved swapping the stock Brembo rotors with some highly effective ones from Disc Brakes Australia.  When traveling to Australia several months ago in part two of our project, we drove a highly modified STi at the track, Whiteline’s infamous P25.  No matter how hard we abused the brakes on the P25 they worked consistently with no signs of fade.  Driving the P25 around on the streets during the week demonstrated that the brakes also worked well when cold with little noise or fanfare.

Project Subaru WRX STI
A racer’s trick is to remove the factory dust shields for better cooling of the rotors.  In the front the shields are easily removed simply by unbolting them.

When queried about the brake’s excellent performance, Jim Gurieff, Whiteline’s Technical Director gave much of the credit to the rotors on the P25 supplied by a fellow Australian company, DBA or Disc Brakes Australia. The DBA rotors have many unique features that are truly functional and help the brakes work better over a wide range of conditions.  Impressed as we were by the P25, we ordered up an identical set of rotors for Project STi.

Project Subaru WRX STI hawk brake pads
Hawk HP+ pads high metallic compound is discernable by their dark semi lustrous color.

Part of the secret to the effectiveness of the DBA rotors is their patented Kangaroo Paw venting system. The Kangaroo Paw design features a series of 144 diamond and tear drop shaped pillars and columns, individually spaced between the rotor faces. This system provides two key advantages. One advantage of this design is the ability to cool the rotor faster than before. This works on the same principal as a turbocharger impeller, designed to draw air through the rotor. As the disc rotor rotates, air is moved through the rotor by centrifugal force. Aerodynamic turbulence generated around the rotors individual pillars and columns helps improve the removal of heat from within the internal areas of the rotor. Whiteline offered some data showing a rotor surface temperature drop of over 100 degrees generated during track testing of the DBA rotor.

Project Subaru WRX STI
The DBA rotor also happens to be good looking as well as functional.

The second advantage offered by the Kangaroo Paw rotor is increased dimensional stability across the disc’s friction face, achieved by the equally spaced pillars and columns. This helps prevent rotor warpage and pedal pulsation during use. These advantages increase the DBA rotor’s efficiency by as much as 20 per cent when compared to conventional rotor designs. A 20 per cent increase in disc rotor efficiency, translates to reduced brake operating temperatures, brake fade, disc rotor stresses, disc thickness variation, run-out and shudder.

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