[wdb]

Since I finally need pads and rotors, I finally bothered to read this thread in its entirety. Great stuff when I first read it, and even greater stuff added since.

A couple of things popped into my mind.

Slotted rotors purportedly help with braking in wet conditions. I am far from the only STi owner to have experienced the terrifying "OMG NO BRAAAKKKEEEESSSSS!!!" phenomenon when first hitting the pedal when the rotors are wet; therefore I'd be very interested in hearing from folks using slotted rotors on a daily driver in wet conditions.

Two piece vs. one piece hasn't been discussed. Perhaps that should be the topic of another sticky, but what are the primary advantages of two piece rotors? I see three right offhand; less weight, less heat transfer to the wheel bearings, possibly better heat dissipation.

Drilled holes vs. cast holes anecdote: I don't know if anyone actually casts holes in rotors or not. What they might do is something Campagnolo used to do to bicycle brake levers back in the 60's when light weight mania first raged there, namely piercing the (aluminum alloy) part while it was being formed. Creating the holes while the metal is still hot has all kinds of metallurgical advantages, elimination of stress points being primary among them. A Campagnolo Super Record brake lever from that era is a marvel of structural beauty. It also weighs exactly the same as the identcal-except-for-holes Record lever, meaning that all those holes were, at the end of the day, strictly for show.

Here's a picture of a Super Record lever.

[Andy STI]

Good stuff in here. I just bought some slotted DBA replacement rotors as my stock blanks were looking pretty thin from tracking the car. I hope these work well, I just didn't see an advantage to pay more than double for 2 piece rotors.

Wdb, way off topic but do you have some Simplex retro-friction shift levers on that bike? I used to love those levers. Nice retro ride btw. I've got a bunch of Super Record and C Record stuff in my basement. Maybe we need a bike post in OT.

[effect]

the Newer pads still create those gasses our rotor technology has just gotten better. now we have Vented rotors which really helps with the heat/Gas desipation.

[Evan]

It's really all a trade-off, having holes in your rotors do make them more prone to cracks, but they do cool them faster as there is more surface area of the rotors exposed to the open air. Also, solid peices of metal, when heated, tend to retain heat in the center of them. Having holes going all the way through gives a way for all that heat trapped in the center to get out, allowing for much quicker dissipation.

[ldivinag]

here's my reason for getting drilled ones:

try driving in the big rain downfall and hit your brakes.

i can repeat on my 04. the first time, i was in the freeway and someone cut me off and i hit the brakes and i felt like i wasnt stopping.

let off and hit the brake again. finally, it started braking.

my theory is that water got trapped between the pad and the rotor and when i did a panic stop, there wasnt time to wipe the water off.


also, on a side note, i was looking at 08 M5s this weekend. the stock rotor is drilled with bigger holes than those that i got from brembo on my toyota truck.

[MGizzle]

Check this link out guys. Also, try and look at the "strapped" floating two piece design. Pretty sick.

Brake Discs, Air Jacks, Brake Calipers, Brake Fluid, Brake Kits, Pads, Clutches, Master Cylinders, Pedal Boxes, Slave Cylinders from AP Racing

Anyhow, I am searching like a maniac all over SAE etc. on some CFD models of brake rotors, but can't seem to find anything. However, reading the link above and talking to a few engineers it sounds like cross drilling is really just for marketing. it doesn't help cool your rotor and I have a hard time believing that air is pulled through the holes when the rotor is forcing air through the veins due to the centrifugal forces. Some people claim this because the Pressure is lower inside the veins than it is on the outside of the disck. Again, I am trying to find a CFD analysis of this to confirm it. Anybody have CFD access??? I have a 3D CATIA model of a vented rotor (blank) and I could draw some holes and slots in it??

However, the reason why this subject is not allowing me to sleep at nights is WHY do sooo many sick cars and race cars use it? Pratt and Miller C6-R, saw it in person torn down and they were drilled significantly. The new Ferrari 430 with carbon composite brakes, the porsches etc. Check out the autoblog.com post of the new 430 ferrari and there is a great shot of the brake discs. I think it is just for marketing again because those rich dudes don't have a clue, but still, I have a hard time believing that Ferrari would do it on such a PURE car if it didn't benefit in some way.

This subject is killing me.

[MGizzle]

Oh I forgot, if you are only using your car for street purposes folks recommend cross drilled and slotted, or just slotted rotors. After arguing with an engineer for a while it made sense why to do this on street applications; Unsprung weight reduction.

On the street you will not have TRACK hot rotors and during a panic brake you will have plenty of power to LOCK UP and go into ABS with cross drilled and slotted rotors. You will hopefully have to do this only a few times during the rotor life.

[EuroScuby]

I frequently track my car on Nurburgring. I installed Project U two piece vented and slotted rotors. Originally, I ordered slotted rotors but received vented and slotted and just went with it to try them out. When I run the first lap of the day, I notice brake fade about 1/2 to 3/4 of the way through the track (13.7 miles). On my second lap, I don't seem to notice the brake fade. I have experienced that "OMG, my brakes don't work" on my stock Brembo rotors after washing my car which I do not experience with my vented/ slotted rotors. Just my experience. I can't determine which is preferable since my car is a daily driver and a track car. My thoughts are that vented/ slotted are definetely better for daily use on the road.

[MGizzle]

Guys, if you would like to know why some of the sickest cars in the world use cross drilled rotors read this SAE paper.

SAE 2006-01-0691 " The Effect of Rotor Crossdrilling on Brake Performance"

Bottom line is they help cool the rotor better than just a blank or slotted rotor. They talk in more detail why and how. However, it has to be properly designed and too many holes will kill the performance. Cross drilled holes pretty much add about 20% of air into the cooling veins depending on design. In some you can add even more and there is another paper by Brembo that talks about this.

Anyhow, the paper shows that the crossdrilled rotor performs better in panic wet events (not in low pressure low temp wet events) and that it generates more friction in many dry cases, even race cars. Also, it redues glazing, pedal travel (because of higher friction) and some more.

I am trying to write a project paper for one of my grad courses on brake rotors and blank vs. cross drilled vs. slotted and during my resesarch I came across this paper. It is awesome. If anybody knows how I can attach it to this forum please let me know. I have a photobucket account and am not able to attach it there. Any ideas are welcomed and I will place the paper online.

However, please don't take this paper as "cross drilled is better". It depends what you are doing. If you are like me and use your DD car to track without changing rotors you might want to consider slotted or blank rotors because a crack in the rotor can mess your system up bad. If you have a comitted race car and don't care about the budget than yeah, crossdrilled might be for you. It all depends on what you want. My biggest choice for not going crossdrilled is that I live in Michigan and that I do some stupid stuff in the winter where the rotors get pretty hot. Now imagine driving those through a puddle of very cold water. Craaaaaaaaaaaaaaack!!!

Enjoy the read, it is long and technical and coffee doesn't help.

[MGizzle]

So here goes a technical paper on the above subject of rotors that I wrote for one of my engineering classes. It shows some good data and some sweet pics I hope folks get something good out of it.

Enjoy!! (sorry last link didn't work, let me try this)

EDIT: Alright, I give up. Can't host this crap anywhere. Let me know if you are intersted in a copy and I can email it. I'll try to get it through somehow else.