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Old 06-24-2001, 04:11 PM   #1
North Ursalia
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Default RS ---> WRX Brake Rotor Conversion Mods Page Up, Part #'s Included

Spent a bit of time with another IClubber fitting the larger WRX rotors to the RS. Have the mods page up, right here http://www.northursalia.com/m.../wrxbrake.html for your approval . Questions and comments are welcome, and I'll try to answer anything I can (but read the page first, then ask your questions, as most of them will be answered there).

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Old 06-24-2001, 05:38 PM   #2
DLC
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I've done this to my 93 Legacy Touring Wagon.

It's really very, very easy and the brake power is incredible.

http://www.xmission.com/~dac/library/brakes.htm
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Old 06-24-2001, 05:47 PM   #3
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I was wondering, can you just switch over bigger rotors without changing the calipers, or do you have to change them too... I have a 95 L with crap brakes, and I want to switch to larger rotors, but I'm not sure if it'll work...?

-Josh
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Old 06-24-2001, 06:05 PM   #4
North Ursalia
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ImprezaL, the RS calipers are larger than those of the 95L I believe, so you would have to change the calipers as well if that is the case. If not, you are only changing the bracket for the caliper- the stock caliper remains.

Brian
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Old 06-24-2001, 06:08 PM   #5
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ImprezaL, I just checked one of my parts books, and it would indeed appear that you would have to change out the calipers as well .

Brian
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Old 06-24-2001, 06:47 PM   #6
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Question

Brian,

If you are using the same size RS brake pads then the swept surface the same as the stock rotor no? Other than a larger heatsink will you get any better stopping power? Maybe I'm confused, I'm not that big on brake knowledge. Does having a larger heat sink outweigh the increase in unsprung weight?

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Old 06-24-2001, 07:03 PM   #7
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Yeah, I thought the only reason to up the rotor size was if you were getting heavy-duty fade.
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Old 06-24-2001, 07:15 PM   #8
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I thought you went bigger to enable larger rotors and pads, increasing the swept surface giving quicker stops. Brakes convert foward energy to heat and having a bigger pad/rotor setup would make more heat over a larger surface area.
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Old 06-24-2001, 08:13 PM   #9
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Increasing the rotor diameter increases mechanical advantage -- I did the math some time ago and came up with 8% or something. There is also an increase in swept area, but the real change comes from moving the pad further away from the axle.

Glenn
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Old 06-24-2001, 08:47 PM   #10
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Wow, you go away for a bit and the thread explodes . Thank you for the much more succint answer than I could have given Mr. Wallace .

Brian
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Old 06-24-2001, 08:53 PM   #11
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I see so the pad now travels a further distance around the rotor because he radious has increased, got it.

Peaty
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Old 06-24-2001, 09:17 PM   #12
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Brian, I did some math:

Stock RS rotors are 10.7" diameter:
Area = Pi*r^2 = 3.14 * (10.7/2)^2 = 90 sq. in.

WRX rotors are 11.4" diameter:
Area = 3.14 * (11.4/2)^2 = 102 sq. in.

(102 - 90)/90 = 13.3%

That means the WRX rotors are only 13.3% larger, not "20% larger". I haven't done the math for the swept area, however. And I assume that's where the "20%" figure came from. Swept area by itself does not affect braking ability. But it does help with resistance to fade. Perhaps it should be touted as "20% more resistance to fade"? Or perhaps more than that even, since the rotors are thicker as well.

Assuming the same rotor material, calipers, brake pad dimensions and pad material, only the effective rotor radius affects the difference in braking ability. I haven't measured the pads myself, but I'll highly simplify things and assume that effective rotor radius is in the center of the brake pad, and that the pad is about 2" tall. Then we get approximately (10.4-9.7)/9.7=7% improvement in braking ability. Hardly the 20% quoted above!

BTW, good job with pics that are nearly impossible to photograph.

-WaC
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Old 06-24-2001, 09:22 PM   #13
North Ursalia
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Eh, I go with what I'm told . Thanks for the hard numbers Wayne... I'll update things. I believe Mr. Harvey has a set of stock front rotors for you or Edwin to wreck on the track . Thanks for the kudos too... the hardest thing to get a picture of is where the caliper bracket meets those pins; I think my crude diagram gives the idea, but I'm going to try and take better pictures of that area using my car in the near future.

Brian
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Last edited by North Ursalia; 06-24-2001 at 09:24 PM.
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Old 06-24-2001, 09:25 PM   #14
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WaC if you would like next weekend i will bring the brakes up to your place if you would like to take any sample or reading or something... also i want to give you the crossdrilled rotors to see if you can make them crack in Montreal..
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Old 06-24-2001, 09:30 PM   #15
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Brian,

If you get your hands on a stock set and the WRX ones it would be cool if you could weigh them on the scale. I'm curious to know the diff.
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Old 06-05-2002, 07:12 PM   #16
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yea what is the wieght diff between RS and WRX rotors?
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Old 06-05-2002, 07:56 PM   #17
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Umm, yeah, back from the dead...

WRX rotors are about 14 pounds. I assume RS rotors are about 1.5, maybe 2 pounds lighter.
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