GiroDisc Brakes for the Subaru Impreza: Which Parts Fit

By Core Brake Parts Tech Team — Circleville, OH warehouse

GiroDisc builds its Subaru rotors around the Brembo brakes on the Impreza WRX STI, not the brakes on a base Impreza or most standard WRX models. The GiroDisc part we carry for the Impreza is the A2-007 slotted two-piece rear rotor pair for the 2004-2007 Impreza WRX STI, and it needs rear pads with a trimmed backing plate. If your Impreza is not an STI with the factory Brembo calipers, GiroDisc rotors are the wrong starting point, and the rotor and pad options further down this page are the better fit.

Why GiroDisc Fitment Starts With the STI Brakes

Subaru gave the Impreza WRX STI its own brake package. The 2013 press kit describes it as a Brembo Performance Brake System with ventilated four-wheel anti-lock disc brakes and Electronic Brake-force Distribution, using 13.0-inch front discs with 4-piston calipers and 12.6-inch rear discs with 2-piston calipers. That is a larger, different system from what the non-STI Impreza uses, so rotors engineered for it will not bolt onto a base car.

GiroDisc lists its Subaru rotors by STI generation:

Before ordering anything, look at the calipers through the wheel. Brembo calipers with four pistons up front and two in the rear point to the STI package. If you see a single-piston sliding caliper, the car has a different system and none of these rotors apply.

The A2-007 Rear Rotor: What You Get

The GiroDisc A2-007 slotted rear rotors for the 2004-2007 Impreza WRX STI are a two-piece, fully floating design. According to GiroDisc, the build uses:

• A proprietary cast iron friction ring, poured in the USA and machined in-house, with curved internal vanes for cooling.
• A hat machined from 6061-T6 aluminum.
• Ten cadmium-plated alloy steel drive pins, Class 12.9 screws with hardened washers, and anti-noise spring washers to control float.

GiroDisc puts each rear rotor at roughly 11 lb against roughly 18 lb for the factory part. Cutting rotating and unsprung weight at each corner is the main street benefit. The company also states that factory brake bias and ABS operation are maintained, because the rotor works with the original calipers. When the iron rings wear out, GiroDisc sells replacement rings, so the aluminum hats can be reused.

Why the Rear Pads Must Be Trimmed

This is the detail that catches people. GiroDisc states that OEM pads and some aftermarket pads have to be modified before they will work with these rear rotors. The fix is grinding the pad's steel backing plate down so it follows the arc of the friction material. Skip it and the pad will not sit correctly against the new rotor.

You have two ways to handle it:

1. Buy pads that are already trimmed. GiroDisc says the pads it sells for this application are CNC-modified at the factory, so they install without extra work.
2. Trim your own. Grind only the steel backing plate, never the friction material, keep the edge even from pad to pad, and check that the pad slides freely in the caliper before you bolt the wheel back on. Follow the instructions GiroDisc includes with the rotors.

Plan on this every time you replace rear pads, not only on the first install. Keep that in mind when you order pads from our brake pad collection for a car running these rotors.

Other Rotors and Upgrades That Fit the Impreza STI

GiroDisc is the premium, lightweight choice, but it is not the only way to improve an STI's brakes. Other parts we carry that are listed for the Impreza WRX STI include:

• 2005-2007 STI front: EBC GD1344 GD Sport slotted front rotors. EBC lists these at 326 mm diameter, 30 mm new and 28 mm minimum thickness, with wide slots and blind-drilled holes. There is also the quieter EBC USR1344 fine-slotted front rotor and the EBC BSD V-slot front pair.
• 2003-2004 STI 2.0L front: the EBC USR1056 slotted front pair and the EBC BSD front pair. These are the imported 2.0L STI models, not the US-market 2.5L car.
• 2008-2014 STI rear: the EBC GD1511 GD Sport slotted rear rotors and the EBC BSD1511 rear pair.

For a 2002-2007 Impreza WRX that did not come with the STI brakes, the Brembo GT front big brake kit adds 4-piston calipers with 326 x 30 mm slotted rotors. A kit this size usually needs wheels with enough caliper clearance, so check your wheels before ordering. You can browse more options in our brake rotor collection.

What to Replace at the Same Time

New rotors deserve a clean start. When you fit GiroDisc or any upgraded rotor to an STI, plan on:

• Fresh pads on the same axle. Old pads carry a wear pattern from the old rotor and will not bed in evenly. For the 2004-2007 rear, that means trimmed pads.
• New brake fluid. Hard driving heats the fluid, and fluid that has absorbed moisture boils sooner. Use the fluid type printed on your master cylinder cap or in the owner's manual.
• Brake lines. If the rubber hoses are old or you track the car, stainless braided lines from our brake line collection give a firmer pedal.
• Hardware. Inspect the pad clips and pins and replace them if they are worn or rusted.

How Hard Is the Install?

For a home mechanic with a torque wrench and jack stands, a rear rotor swap on an STI is a moderate job. The two-piece rotor bolts on like the factory part and uses the original caliper. The extra work is the pad trimming, and bedding in the new pads and rotors afterward. Torque the caliper bracket bolts and the wheel lug nuts to the values in the factory service manual, and pump the pedal before driving to push the pistons back against the pads. Follow the bed-in procedure from your pad maker before any hard stops.

Frequently Asked Questions

Do GiroDisc rotors fit a base Subaru Impreza?

No. GiroDisc lists its Subaru rotors for the WRX STI, which uses Brembo 4-piston front and 2-piston rear calipers. A base Impreza has a different brake system, so these rotors will not fit it.

Why does the A2-007 need trimmed rear pads?

GiroDisc states that OEM pads and some aftermarket pads must have the steel backing plate ground to match the arc of the friction material before they will work with these rotors. GiroDisc's own pads for this car come pre-trimmed.

Does the A2-007 fit a 2008 or newer STI?

No. The A2-007 is listed for 2004-2007 STI. GiroDisc lists a separate rear rotor, A2-095, for the 2008-2017 STI. For 2008-2014 rear rotors, we carry the EBC GD1511 and BSD1511.

Will lighter rotors change my ABS or brake balance?

GiroDisc says factory brake bias and ABS operation are kept, because the rotors work with the stock calipers and keep the factory setup.

Can I replace only the iron rings later?

Yes. GiroDisc sells replacement rings for the STI rotors, so you can keep the aluminum hats and replace only the worn friction ring.

Sources

1. GiroDisc - Subaru WRX STI (04-07) Rear Rotors A2-007 - construction, 11 lb vs 18 lb weight, trimmed pad requirement, bias and ABS notes, replacement rings
2. GiroDisc - Subaru WRX STI (08-17) Rear Rotors A2-095 - 2008-2017 rear fitment and pad trimming requirement
3. GiroDisc - Subaru WRX STI (04-17) Front Rotors A1-007 - front rotor dimensions, weight and minimum thickness
4. Subaru U.S. Media Center - 2013 Impreza WRX STI Press Kit - Brembo system with 4-piston front and 2-piston rear calipers, disc sizes, ABS with EBD
5. EBC Brakes Direct - GD Sport Series GD1344 - 326 mm diameter, 30 mm new and 28 mm minimum thickness, slot and drill design