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      11-09-2009, 10:05 PM   #1
rzm3
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Arrow New Theory About Stock Brake/Pads Overheating

So I was inspecting my suspension after a track weekend today, and I noticed that the cross drilled holes on my front rotors were almost completely filled by brake dust...

I know that the stock pads are notorious for being very dusty, so I guess on the track under heavy braking, all the brake dust starts to collect in the cooling holes, thus blocking the passage of air radially through rotor into the vanes to adequetly cool the component. This then leads to the overheating of the rotors and all hell breaks loose.

From my understanding most people with better brake fluid, SS lines, and track pads can run w/o major issues. So I guess the stock pads are what really causes the brake failures?

What do you all think?

(image borrowed from the other thread, notice how the holes are plugged)

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      11-09-2009, 10:23 PM   #2
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The stock pads probably can't handle as much heat as a track pad which will have a high-heat compound which is probably a lot harder than the stock pad. So your stick pads get hot and spongy which leads to fade.

I don't think the dust in the holes makes much of a difference.
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      11-09-2009, 10:24 PM   #3
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My understanding is that the holes are meant to evecuate the gases from the pads, so they are not cooling holes. My guess is that they do not have any significant effect on venting of the rotors/air flow. That is mainly a function of the internal vane geometry and air supply (radially) to the internal vanes. I've seen some interesting CFD analysis reports on this.
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      11-09-2009, 11:17 PM   #4
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Agree, the holes do virtually nothing for cooling. The cooling is done primarily by the internal cooling vanes which have no relation to the drilling. Have you ever seen a real race car with cross drilled rotors?
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      11-09-2009, 11:37 PM   #5
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Yes I have, but slotted rotors must have a different internal vane geometry vs. drilled. If the drilled holes have no cooling use at all, why did people come up with them in the first place?

So how do slotted rotors evecuate the gases from the pads since they do not have the holes?
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      11-10-2009, 01:55 AM   #6
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Quote:
Originally Posted by rldzhao View Post
Yes I have, but slotted rotors must have a different internal vane geometry vs. drilled. If the drilled holes have no cooling use at all, why did people come up with them in the first place?

So how do slotted rotors evecuate the gases from the pads since they do not have the holes?
The drilled holes are there to clear water off the face of the rotor as well as provide a place for hot gas from the face of the pad to vent away. Modern brake pads don't outgas as much as they did 20 years ago, so the venting is less of an issue.

They aren't intended to cool the rotor.

What may be happening though is that brake dust can go through the holes and fill up (then totally block) the airway between the cooling vanes inside the rotor. I doubt this would really happen, but my wheels used to get lovely "spots" on them where the holes on the edge of the rotor threw brake dust out at speed with stock pads.

Slotted rotors vent outgassing from the pad by channeling it radially through the slots out past the edges of the pad. The gas and dust don't share the airway inside the rotor. It's not as good for wiping water, but it's still pretty good, and in the end it doesn't weaken the disk like drilling or cast-in holes do.
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      11-13-2009, 03:37 PM   #7
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The post above makes a lot of sense. But i cant imagine the cross drilled holes would play no roll in cooling even if thats not the main purpose for them. Im not saying the dust is the reason the brakes fade like they do, Im just saying the holes most likely cool faster than brakes with no holes.

Mine look the same if not worse

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      11-13-2009, 08:17 PM   #8
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When I wash my car, just spraying down the wheels clears out most of the dust. I can't imagine that it is a huge hinderance to air flow through the holes.
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