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- - Impreza WRX rotors (https://www.ft86club.com/forums/showthread.php?t=107979)

Impreza WRX rotors

So I heard in the German FT86 forums somone suggesting to use the 2002 Impreza WRX rotors as an upgrade option. The user stated, that those rotors are proven to be "better" by experience. He mentioned Brembo 09.9077.10 which are in fact the same size than the "original" Brembo 09.A921.14.

Does anyone know what the difference between the two is and why the WRX rotors should be better? :iono:

I don't know which year range is applicable, but the WRX rotors are the exact same part as the factory FRS/BRZ/GT86 rotors.

I would ask how they were better by experience... longer wear? There's nothing wrong with the stock rotors, I got over 100k km's on mine with lots of track use.

Quote:

Originally Posted by wparsons (Post 2697159)

WRX rotors are the exact same part as the factory FRS/BRZ/GT86 rotors.

I'm not so sure about that - I checked the technical drawings for the FT86 rotors (Brembo P/N 09.A921.14) and I noticed that the WRX rotors (Brembo P/N 09.9077.10) have a wider gap for ventilation (7.5 mm vs 9 mm). Brembo also mentions that there are fewer ventilation fins in the WRX rotor.

Quote:

I would ask how they were better by experience... longer wear?

I don't know. I guess they tolerate more aggressive pads? Due to the wider venting gap I would also assume, that cooling is improved?

Quote:

Originally Posted by Flasher (Post 2697913)

Is the rotor thickness the same on both? If so, the ones with a wider gap actually have less thermal capacity due to less metal. They could end up running hotter despite having more air space.

Quote:

Originally Posted by Flasher (Post 2697913)

I don't know. I guess they tolerate more aggressive pads? Due to the wider venting gap I would also assume, that cooling is improved?

Per above, if the rotor isn't thicker but the inner air space is increased you've removed thermal mass and in the process given the rotor less material to wear off before it becomes too thin. 1.5mm isn't a huge amount, but it still less metal to wear and/or absorb heat.

Which of the rotors is a newer revision? I would bet the WRX parts are old, and have been replaced across the board by the new FRS part, even for WRX fitment.

Quote:

Originally Posted by wparsons (Post 2698090)

Is the rotor thickness the same on both? If so, the ones with a wider gap actually have less thermal capacity due to less metal. They could end up running hotter despite having more air space.

Per above, if the rotor isn't thicker but the inner air space is increased you've removed thermal mass and in the process given the rotor less material to wear off before it becomes too thin. 1.5mm isn't a huge amount, but it still less metal to wear and/or absorb heat.

Which of the rotors is a newer revision? I would bet the WRX parts are old, and have been replaced across the board by the new FRS part, even for WRX fitment.

So this is the WRX part

https://www.bremboparts.com/en/catal...c-fb4afd056fb7

And that's the FT86 part

https://www.bremboparts.com/en/catal...8-5416ebe21c5c

Dimensionwise the parts look identical except for the gap in the middle. As for the age of the parts - the WRX technical drawing has a more recent date (2014 vs. 2013). Dunno if that is also applicable for the design, or just the drawing.

So as wparsons was mentioning, the diagram seems to show the FRS rotors actually having more rotor material to be used than the WRX rotors. The 1.5mm difference is given to the rotor side of the equation, giving the FRS discs a slight thermal edge. Ofcourse this is 2002 WRX brakes.

OK I know that bigger rotors are better performing due to the bigger surface, higher heat capacity, and better cooling but does that also apply for rotors with only a weight difference?

I assume that you can put more heat in heavier discs, while the lighter rotors have an advantage in cooling?

If they changed it to add more material there must have been a reason. It would have been cheaper to use the existing old part.

Just my opinion.