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Old 02-04-2009, 11:05 AM   #1
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Default SUBARU: RB calipers vs. Brembo and other calipers

The following is a message originally posted on 9/8/08 at

We recently received an inquiry about what makes our calipers different from Brembo or Subaru WRX 4-pot calipers. Below is the question as well as our response.

Originally Posted by ewong_kaizen

Why should I get a RB caliper versus say a WRX 4pot or Brembo?

Yes - I read the stuff about the move out kits etc. What I wanted to know is what (if anything) makes your CALIPERS better than say Brembo?

Here are key features of RB calipers:

1. Caliper material and overall construction:
RB Caliper bodies are made from forged aluminum and precisely machined to every detail; while those stock calipers - Aluminum (Brembo) or Cast Iron (Newer WRX) calipers are in mass production and are usually made through a casting or extrusion process which is not as dense and strong in structure as forging. Also if you compare to WRX’s 4-pot caliper there is a substantial weight saving in aluminum calipers.

2. Caliper mount:
RB calipers are mounted to the adaptor (with two high strength alloy steel bolts) in a radial direction (top mount) - from the caliper down to the adaptor, whereas stock Brembo and CI fixed piston calipers are mounted in an axial direction (side mount), from the spindle to caliper. A top mount caliper is more rigid than those side mount calipers which typically used in stock calipers.

3. Piston material:
RB calipers use stainless steel pistons (RB4000, RB400 and RB600 models) vs. Brembo and other manufacturers' aluminum pistons. Stainless steel transfers about 1/10 the heat of aluminum, resulting in significantly less heat transfer from the pads to the brake fluid. Stainless steel is also more rigid and higher in strength than aluminum. Being that stainless steel has comparable melting temperature (2700 def. F) as brake pad steel backing plates, the pistons will never melt to the pad backing plates. Aluminum pistons (1220 deg. F) can melt to brake pad backing plates under extreme high speed braking.

4. Piston seals:
RB calipers have double seals – Inner one for brake fluid and outer one for fluid and dust, while those stock calipers typically use dust boot (instead of seal) which can easily be torn out.

If you compare the performance, durability and maintenance cost all together, clearly RB calipers are the right choice.
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Old 02-04-2009, 11:07 AM   #2
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How do you compensate for the front bias on Subies with your BBKs?
This is a very generalized and broad question and we will try to explain as follows:
Brake bias adjustment can usually be achieved by a variety of changes,

1. The rotor size (torque arm)
2. Brake pad compound (coefficient of friction)
3. Caliper piston size or installing proportioning valve (brake pressure)

There are pros and cons for different modifications to obtain optimum brake balance but based on our observation and extensive experience in brake design, we believe #1 and #2 are the most effective way.

To adjust bias, the entire front-rear system must be looked at as a whole. For example to reduce front bias, the most common practice is to increase the rear braking power. RB offers several front and rear upgrade options to allow customers to adjust any bias for optimal balanced system.

There is hardly one setup that is optimally balanced for all. Even each driver's braking condition (e.g. how sharp of the turn and how you tap the pedal) can generate different biases with the same setup.

Our rotors kits were designed to make up the deficiencies of Subaru stock set ups. To better understand this, here is an example.

Rotor sizes of the early Forester model (98-2/02):

Front: 277x24 mm (10.9"x0.94")
Rear: 266x10 mm (10.5"x0.4")

The brake bias in this setup was balanced, but Subaru likely felt that there was not enough overall braking power, so they increased the front brake rotor size for the late model Foresters:

Rotor sizes of the late Forester model (3/02-08):

Front: 294x24 mm (11.6" - Increase from 10.9")
Rear: 266x10 mm (10.5" - No change)

Although Subaru increased braking power in the front, they kept the rear brake rotor size unchanged! This likely led to the increase of front brake bias, so Subaru recently changed their brakes again for the 2009 Forester, enlarging the rear rotors:

Rotor sizes of the 2009 Forester:

Front: 294x24 mm (11.6" - No Change)
Rear: 290x10 mm (11.4" - Increase from 10.5")

Long before the 2009 Forester was released, RB had offered this rear 290x10 mm BBK upgrade kit. Many Forester owners have installed this kit to make up for the rear braking deficiency and to catch up to the latest design for a more balanced brake system.

In the future, for '09+ models, if Subaru decides to upgrade the brakes further, RB will have already been providing BBK upgrades for a long time, with our soon-to-be released 322x25 (front) and 316x18 (rear) big brake kits.

A better balanced brake system is definitely a wise investment for any car owner, not only for driving safety but also to lower maintenance costs. RB is proud to serve the Subaru community with effective yet affordable brake upgrades.
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Old 02-04-2009, 11:08 AM   #3
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To summarize all above discussions, and keep up to the latest (2009) Forester set up for a more powerful and better balanced brake system, It can be concluded that the following investment is definitely worthwhile:

For those pre-2002 owners - To upgrade both FRONT AND REAR BBK.

For those 3/02 to 2008 owners - To upgrade the REAR BBK.

We think Subaru has perhaps the most confusing and illogical stock brake set up than other car makes, but we keep track of them and hope this clarification is helpful to your decision.
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Old 09-02-2012, 07:52 PM   #4

There while those stock calipers typically use dust boot (instead of seal) which can easily be torn out....

love me little,love me long!!
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