Rotors

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avriette
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Re: Rotors

Post by avriette »

zaxrex wrote: If you are repeatedly doing 100+ and throwing down the anchor, your ass had better be off public roads.
You know, I didn't use the words "public roads" or "street" at all. I just wanted to quantify my experience with fading of the Subaru's brakes, not comment on the law of the land. I felt that somebody had understated the fade characteristics, or overestimated the heat dissipation capacity of the brakes on the car. I made a small comment because I realize I'm in the minority in this belief (which is to say many people hold the exact opposite belief). I don't see any reason to expand the discussion to include when, where, and how to use your left and right feet. I think we all agree there's enough of that going on elsewhere. :chill:
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Mr Kleen
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Re: Rotors

Post by Mr Kleen »

avriette wrote:i disagree -- i think the stock brakes (on the sti) fade pretty easily.
I've never heard that. :? slotted rotors alone aren't going to help with fade, pads will.
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Re: Rotors

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Mr Kleen wrote:
avriette wrote:i disagree -- i think the stock brakes (on the sti) fade pretty easily.
I've never heard that. :? slotted rotors alone aren't going to help with fade, pads will.
Wha? Slotted rotors are slotted to get gasses off the surface of the rotor, to provide venting, in essence, on the front (as they are usually vented in the "back" as well). They also serve to reduce glaze on the pad (by continually scraping at it), and to increase the surface area of the rotor (which is why we sometimes see much more aggressive slotting than the usual).

Pads, I guess, could reduce fade, depending on the compound, but at the end of the day, you want heat off the rotor, and out of the brake fluid. The pad's job is to create friction. Am I missing something?

(people will also tell you the STI has a limiter at 145... it's amazing the things you "don't hear" and will "find out" and be surprised by, which is the only reason I bring them up)
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Mr Kleen
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Re: Rotors

Post by Mr Kleen »

every article I've ever read about brake system upgrades has said that modern pad compounds don't off-gas. anybody have hard info on this?
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Re: Rotors

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Mr Kleen wrote:every article I've ever read about brake system upgrades has said that modern pad compounds don't off-gas. anybody have hard info on this?
I'm going on stuff I read in college in 1997 Gabe. I could be dead wrong, hence asking if I'm missing something.
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Re: Rotors

Post by Libra Monkee »

:popcorn:
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Re: Rotors

Post by avriette »

Libra Monkee wrote::popcorn:
:)


You know in some ways I am bummed when I learn I'm a dinosaur and I totally misunderstand "modern brakes" or a similar topic. But at the same time, it's cool to learn that technology has advanced since I was in school. I'm just as :popcorn: as you here, bro.
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Re: Rotors

Post by zaxrex »

Sorry, I will use less ass in my responses in the future. I just thought it was funny that you were disagreeing with Gabe's track comment with an example of something that most would only attempt on a track.

My pertinent contribution to this is the drilled rotors issue.

If rotors are drilled then heated and annealed, there will last a longer time before cracking.
One good thing about drilled rotors is they give tons more surface area and venting capability. This cools down the rotors quickly, among other things. The bad thing about drilled rotors is that they give tons more surface area and venting capability. This cools down the rotors quickly.

When there are temperature changes, the material submits to thermal expansion based on its material properties. Some of the poorer brake designs with solid rotors would bow because the hub would not heat up but the outer rotor surface would. The edge grew but the center didn't, so the rotor would warp. But that is a little side track, sorry.

With all this with this repeated and rapid differential heating, the "grain" or metallic lattice structures start binding and stop sliding over each other. This makes the metal stronger, but more brittle. The biggest temperature differential is around the drilled holes, since that is where the cooling air goes through. This is the area with the most thermal stress and embrittlement. The results are cracks. See my rotors.

Annealing rotors after they are drilled helps delay this problem.
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Mr Kleen
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Re: Rotors

Post by Mr Kleen »

I need to research this "off-gassing" thing a little more, just to be sure I'm going on the correct info, but I've seen it stated in more than one magazine that I trusted at the time but don't remember now that I'm on the spot :oops:


this is the best I can find on short notice:
Finally, it is important that the brake material has a slot in the middle of it. This is not something most people consider or even notice. Brake pads used to be made out of asbestos, which would give out gases when heated to extreme temperatures. These gases would get trapped between the pad and rotor and cause inefficient braking. Slotted and drilled rotors were designed to give the gases some place to go. Modern brake pads no longer out-gas after you have bedded them in. However, it is possible to have a small amount of brake pad material to burn off during heavy braking. When any organic material burns, there is a chemical reaction and it gives off vapors/gas. To make sure this doesn’t become a problem, quality brake pads have a slot down the middle to give the vapors or gas someplace to escape.
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Re: Rotors

Post by snaab »

Mr Kleen wrote:I need to research this "off-gassing" thing a little more, just to be sure I'm going on the correct info, but I've seen it stated in more than one magazine that I trusted at the time but don't remember now that I'm on the spot :oops:
I don't think you're too far off. I bought my slotted rotors, 'cause the rotors needed replacing, the slotted ones were not much more money, and they look cool.
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Mr Kleen
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Re: Rotors

Post by Mr Kleen »

I can't disagree with you there. 8)
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