# moding brake rotors



## p10driver (Apr 30, 2002)

I bought some Brembo rotors for my P10. They are 256x22.
Now I hope that I can find someone who can cryo them( when you live in Slovenia that's not so easy )...

And I would like to slot or drill them (or maybe both). What do you think of it? Has anyone before slotted or drilled stock rotors??


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## ryan7o7 (May 6, 2004)

Drilling and slotting just gives you more friction on stopping. Slotting them must be done at an angle. It can be done with a saw, come down vertically till it cuts about a 1/8 in slot.
Drill holes with any drill you have at your house, drill a lot of small holes in a zig-zag pattern


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## chimmike (Oct 17, 2002)

don't worry about cryo.


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## p10driver (Apr 30, 2002)

My friend will do the slotting at work. They have a machine. I've decided to do 8 slots and this gives a angle of 45°. I still don't know if i'll drill them or not...

Why should i not worry about cryo? Is it not as good as people say??


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## chimmike (Oct 17, 2002)

it's just not necessary. I've never heard of anyone cryo treating their brake rotors. If you have brembo blanks, chances are you'll never exceed the capacity of them.


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## p10driver (Apr 30, 2002)

thats pretty nice to hear 

Look at www.frozenrotors.com they swear on it. And Mike K. has written: "Cryo treating your rotors makes them last up to 100% longer." 
Hm? Will se if I can find someone who can do it right....


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## ReVerm (Jan 13, 2003)

p10driver said:


> Why should i not worry about cryo? Is it not as good as people say??


People do cryo treat rotors. It's just that no one's ever offered any scientific proof that it would provide enough of a benefit to justify doing it, so a lot of people just avoid it.

Don't drill your own rotors unless you can chamfer the holes though (especially not in solid rotors, where the stress in the metal is less evenly distrubited through the rotor when you drill). They'll crack, deform, and/or chip, even during street use.


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## p10driver (Apr 30, 2002)

I know that I need to chamfer the holes. My rotors are not solid they are vented... 

I drilled some solid rotors before on my old car (Opel Ascona 1.9SR) with no problems but it was a old solid German oversize engineeried car  ...

Will see how the rotors work, when they come back from slotting, in combination with TEXTAR pads and decide then if drilling is needed...

What about installing some flap on the lower arm to bring more air to the brake to keep them coll. Or maybe some flexpipe from the front bumper??


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## Ninety-Nine SE-L (May 5, 2002)

LOL, it's funny listening to people's opinions about cryo treating. Actually, I'm trying to find a place to cryo my rear rotors. From what I understand (and I'm studying materials), at the low temperature, some metals change their crystal structure. I would assume this helps remove voids and imperfections in the metallic structure. 

Molecular imperfections are why things break. For example, a ceramic coffee mug. The concept is, if you can make a ceramic mug out of 100% ceramic free of all imperfections, you could throw the mug as hard as possible at a hard surface and it would not break. It is the fact that it is not pure and that it is full of cracks and molecular imperfections that ceramic has a tendency to shatter. Certain methods can be used to reduce the amount of inperfections in a material (examples: forging, heat treatment, cryo treatment, and diffusion).

I am also sure that metals of higher quality (by this, I mean pureness) have higher conductivity (thermal and electrical) and can take more stress before they fracture.

If you're looking for proof of how well cryo treating works, lemme see:
>Cryo treated gears can take more hp before you chip a tooth. Many high performace cars use Cryo treated gearsets.
>Racing brakes and brakes on emergency vehicles are usually cryo treated, they have been reported to last 3-4 times longer.
>I'm almost 100% sure my powerslot rotors are cryo treated out of the box. After over a year and a half use on 2 cars, they have yet to show rust on ANY surface.
>Someone posted a while back that he has a lawn mowing service, when they started cryo treating the blades, they reported that the blades lasted 6x longer before sharpening or replacement.
>If Mike Kojima recommends it, I would have to believe it.


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## bahearn (Jul 15, 2002)

> Drilling and slotting just gives you more friction on stopping.


Nope. You just reduced swept area. You get less stopping power (though the difference is slight).

The advantage to slots is supposedly keeping the friction material cleaner and to provide a path for gases generated during braking to escape from between the pads and rotor.

Cross-drilling is to reduce unsprung weight and rotating mass. Cooling is not enhanced. Proper cross-drilling requires chamfering each hole on each side of each surface. This removes sharp edges that are stress risers. Cross-drilled rotors are proven to be more prone to cracking than solid rotors.


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## Ninety-Nine SE-L (May 5, 2002)

correct. A layer of gases forms between the pads and the rotor. The slots provide an escape for the gases. Cross-drilling ruins the structural integrity of the rotors, it creates stress points and leads to cracks.


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## Matt93SE (Sep 17, 2003)

Pads gassing out is a leftover remnant from the old days of organic pads. NOBODY runs organic pads anymore, so outgassing is hardly an issue.

Don't bother cryo treating your rotors either... Buy quality rotors and it's not an issue. Brembo is a quality rotor. I've cryo'd a couple sets of rotors on my car and noticed no difference in longevity. Honestly, the cryo'd rotors wore out and cracked faster than the non-cryo'd rotors. (and yes, I had them done at a good shop. Cryogenics of Tulsa. All the guy does for a living is build race cars and cryo treat parts for cars and industrial uses... he knows what he's doing.)


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## ReVerm (Jan 13, 2003)

Matt93SE said:


> Pads gassing out is a leftover remnant from the old days of organic pads. NOBODY runs organic pads anymore, so outgassing is hardly an issue.


Actually, that's not entirely true. Even modern semi-metallics out-gas (albeit not as much as pads from the old days). If they didn't, things like green fade wouldn't be a problem any more.


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## Matt93SE (Sep 17, 2003)

Green fade is a slightly different beast. that's why you bed pads before doing any hard driving on them. outgassing on today's pads are orders of magnitude lower than the old organic stuff, and generally that's only until the adhesives in the pad cure completely- or cook themselves off.


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## Ninety-Nine SE-L (May 5, 2002)

Actually, I would like to revise my previous statement. In Materials, there's a term we refer to as crunchy on the outside, soft on the inside. It refers to carbonization diffusion of steel. As you should know, Steel is iron and carbon. The addition of carbon makes the material harder. Low-carbon steel is softer and more ductile, high-carbon steel is harder, but more brittle. In this diffusion process, carbon is added to the outside of a steel object (like a gear) and the carbon level increases on the surface faster than on the inside. It makes for a very hard material that is backed by a softer, more ductile material.

Anyway, I'm still a bit uninformed about how the cryo process works, but I would say it does make the material harder. Keeping in mind hardness is related to brittleness, you have to give up one factor to obtain another. 

If you look at a stress vs. strain graph (link below), you sould possibly get a better idea about what I'm talking about. For reference, we'll say a cryo'd rotor is "ceramic-like" and a non-cryo'd rotor is "ductile"

Ceramic-like materials can take much more heat/stress without any sort of deformation, however it has a tendency to fatigue* very quickly leading to fracture/failure.
Ductile materials cannot take as much heat/stress as a ceramic-like materials, however, they don't fatigue* as easily. Instead of fracturing, they warp or deform way before they fracture.

*Fatigue refers to failure of a material due to cycling. Such as many heating/cooling cycles.

Because of this Ceramic-like rotors would be choice in a racing application. They can take much more heat without warping/deforming. However, they have limited fatigue, you cannot go through many heating/cooling cycles before they crack. 

Ductile rotors are a choice in daily driving. They cannot take as much heat as ceramic-like rotors b/c they have a tendancy to warp or deform, but they don't fatigue as easily, so you can run more hot/cold cycles before any fracturing happens.

I hope this clears things up.

PS. If you want to see a graph of this, go to page 9 of the following document:
http://www2.mmae.ucf.edu/~ysohn/Lectures/Mechanical Behavior One.pdf

legend:
red: ceramics
blue: metals
green: plastics
Stress: applied force or heat
Strain: deformation of the material
when the line ends, the material has fractured.


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