Cross Drilling rotors

[myshtern]

How difficult is this to do?

I dont want to buy new rotors but have heard of people cross drilling their current rotors. The reason I am saying this is because I plan on doing some autocross and Kia brakes blow ass. I expect them completely overheat after something like 2 laps.

Think some cross drilling will help this?

How would I go about doing it?

[Mario]

I don't see what's so attractive about this...

http://www.kimble.org/pictures/1000x656/kimorg-20010429-121819.jpg

http://www.kimble.org/pictures/1000x656/kimorg-20010430-153932.jpg

[myshtern]

Well i obviously dont want to crack them

I just want to get some cooling in there

[Weston-work]

There was someone who did this to an Integra with good results, but he carefully chose where to drill and used a drill press.

However, it's not going to be of any benefit to you. Your brakes will not overheat at an autocross... you only run through the course 3 or 4 times, with good 15-30 minute breaks in between. It would be another story if you went to a road racing track, such as Second Creek, but the place to start there is pads. Better pads will grip better and handle more heat. How well they will work will depend on the kind of pads. Axxis Ultimates are a good street/autocross/track pad in most cases. Good fresh DOT4+ fluid is needed too; Valvolene SynPower brake fluid is cheap, easy to find, and works well.

As for rotors, most road racers run regular blank rotors, and there doesn't seem to be any real consensus about drilled or slotted rotors being worthwhile or not. I think it really depends on the car, the driver, and the track. However, it is pretty widely agreed upon that rotors that are both drilled and slotted are nothing but "tuner" garbage; same goes for dimpled rotors.

[Mario]

Well i obviously dont want to crack them

I just want to get some cooling in there

Cooling in what? Get good pads, get some blank rotors from Autozone for your car, and enjoy. I know many people using that setup for AutoX.

[Weston-work]

As for drilled rotors cracking, the culprit there is really the quality of the metal used in the rotor. I've cracked the shit out of cheap blank rotors (ValuCraft brand; $16 at AutoZone), just from a month or two of street use. Light surface cracking is ok and normal for a performance street/track pad, but those cheap rotors were cracked all the way through (like in that pic above).

However, a slightly better blank rotor (Aimco brand; $21 at AutoZone) turned out to be much better... they don't even crack when using my road racing pads, which are extremely hard on rotors. And there are also plenty of better rotors on the market that should be even more resistant to the abuse of full race pads.

The same quality of metal issue applies to drilled or slotted rotors as well... Some are cheap and will crack, but others wont. Drilled rotors are obviously more prone to cracking than blank rotors made of the same metal, but if the material is good, they shouldn't crack in either case.

[myshtern]

Is the $21 price for a pair?

[Mario]

Per piece.

[Weston-work]

For my car, it's $21.99 per piece for the front. It will be different depending on the car. But there's no need to replace your stock blank rotors, unless they are badly cracked or warped.

[myshtern]

As far as slotted and cross drilled rotors, wouldnt it be logical though that they ventilate better?

[wild.irish]

i just ordered blank brembo's at nopi.com for like $25 each.

as for cross-drilled/slotted, it is my understanding that you might start to feel the benefit, if you also go with big brake conversion kit. i mean, those slots on a stock-size rotor would not do any good. if you get a bigger size rotor, it probably would be noticeable. Anyone experienced, correct me here if i'm wrong.

[Robie]

Good luck on drilling them. :rolleyes:
Using anything but a water cooled machine will only cause the rotors to lose there temped strength. You would have to drill them in a tub of cold water, and keep the water cool during the whole process.

If you want them, and want the benefit of them, I would recommend using EBC Green or Red Stuff pads. Green Stuff for tearing around town, etc. . .Red Stuff for Autocross day--ONLY. Those coupled with the cross drilled/slotted rotors is where you will see your money's worth.

Here are mine...Milled and Zinc coated. . .
http://www.highaltitudeimports.com/gallery/watermark.php?file=500/1232front-rear2.jpg

Robie

[chrisbarnett01]

Cross drilled rotors are MORE likely to overheat than standard rotors. When you drill holes, you are taking away material that can absorb heat.

With modern pad compounds, cross drilled rotors do jack, except in the rain, where they allow more consistent stops, as water can't build up between the pad and rotor.

Weston, rotors from Autozone SUCK. Measure them, check them for warpage. Seriously, you'll be surprised. Most of the rotors they sell are at the minimum thickness of most vehicles factory specs. Not good.

For just a little more $$ per rotor, you can get Brembo OEM replacement rotors, which are by far the best stock replacement rotors in existance, except for maybe OEM rotors on some vehicles.

[Weston]

There are a few different brands at AutoZone. The rotors I get from there (Aimco brand) have been great for me, and a lot of Honda road racers use them regularly. I've never measured them, but my race pads put some major wear on them and they handled the abuse with no problem. There was so much wear that it created a pretty good lip on the outer edge, and the thickness of the contact area had a pretty noticable gradient from the inside to outside. I wouldn't imagine they are within spec now, but they still aren't exactly disintegrating or even cracked. (obviously, I'm not using them any more.) I know there are better rotors that wouldn't wear as fast, but I don't think it's bad at all for $21 rotors, especially considering that I was lazy and drove to and from the track twice with those nasty track pads on (not at all street pads; eats the shit out of rotors, especially when below 300F).

But like I mentioned earlier, there are several kinds of rotors available at AutoZone... the really cheap ones carry the ValuCraft name and are junk. I've had many sets of the Aimco rotors and they have been great. The only time they have ever warped is when I used crappy pads, but I've warped Brembos the same way. And there has never been any more than light surface cracking on them, which quickly disappeared when I put the race pads on. However, the ValuCrap rotors cracked all the way through in less than 2 months of only street use, so there's a huge difference in quality.

[doctorstupid]

to chime in, i think for autoX you'd be just fine with DOT4 brake fluid and better pads. the fluid i got is motul600, boils at 600*F (hence the name). good shit, kind of expensive though at almost $15/pint, but i only need 2 pints for the whole system so it's all good.

[Robie]

Cross drilled rotors are MORE likely to overheat than standard rotors. When you drill holes, you are taking away material that can absorb heat.


It doesn't work like that. . .

The Holes/Slots are designed to allow super heated gasses (and dust) escape that are generated between the pad and rotor. That is what 'Brake Fade' is.
The slots/holes also aid in cooling as the rotors get heatsoaked quite quickly. They increase the surface area of the rotor exposed to the atmosphere. It is the same principal behind a radiator/intercooler--the fins increase the surace area--the more exagerated the fins, the greater the cooling efficiency (Ever see a solid block of aluminum for a radiator/intercooler?).

There is a reason every rally car through F1 racer uses cross drilled/slotted rotors. . .brake fade is deadly.

The DOT4 and higher brake fluid are an important part of this formula. . .they resist higher heats-and don't boil, reducing the chance of bubbles in the lines and caliper chambers.

Brake pads that have Ceramic/carbon fiber/kevlar, etc. and copper mixtures are another important mix. Copper is an extremely good conductor of heat, which pulls the heat away from the rotor and dissipates it quickly. The Ceramic/carbon fiber/kevlar, etc, keeps the pad itself from melting from all the heat it is transfering.

One last thing, Brake lines. . .OEM brake lines tend to flex quite a bit, and that gets exagerated when the fluid inside heats up. That expansion reduces the actual energy transfered to the caliper assembly, causing a 'mushy' braking sensation. To combat this, Steel braided brake lines reduce this expansion, allowing more energy to be transfered from your foot, to the caliper.

It is all about heat and the byproducts it generates.

Brake Theory 101. . . class dismissed. . . :cool:

Robie

[chrisbarnett01]

It doesn't work like that. . .

The Holes/Slots are designed to allow super heated gasses (and dust) escape that are generated between the pad and rotor. That is what 'Brake Fade' is.


Modern compounds create no gasses. 20 years ago, it was different, and slotted/drilled rotors made a difference for street cars. Nowadays? Nothing as far as gas production. Dust is a different story, but dust doesn't function like a gas would on the brakes. Dust doesn't really hurt the braking action too much, since the dust is actually mostly brake pad compound.

Brake fade is when the brakes overheat and require more effort to exert the same stopping force, or just stop working all together. Hence runaway truck ramps.

And Robie, AFAIK most Lemans, all F1, and most WRC cars use NON slotted/drilled rotors. Most of the upper end cars use carbon rotors, and I've never even heard of a crossdrilled carbon rotor. I'm not a brake god though, so I don't of everything that is out there. All the photos I've seen of F1 and WRC cars show non drilled rotors, and the Ferrari F1 car I looked at last year at SEMA 03 had non drilled rotors. I dunno if they were race spec though.

Also, as for brake cooling, most rotors are vented. Crossdrilling actually weakens the effectiveness of good brake vents. Sounds opposite of how it looks, but a simple science experiement could show it. Maybe at SLOW speeds they work better.

[Robie]

Brake fade is when the brakes overheat and require more effort to exert the same stopping force, or just stop working all together. Hence runaway truck ramps.

You aren't explaining what the heat causes though. . .just that it requires more force. Glazing of the pads is one of the results. . .no matter what the compound, and that still happens.


http://www.stoptech.com/whitepapers/warped_rotors_myth.htm
http://www.stoptech.com/whitepapers/stainless_steel_lines_q&a.htm

http://www.f1technical.net/article2.html
"The discs are often drilled so that air will flow through and keep the temperature down."

http://www.mrtrally.com.au/performance/brakerotors.htm

http://www.brembo.com/ENG/Racing/News/List/20040404.htm

http://www.brembo.com/ENG/Performance/GranTurismoBrakes/

http://www.wilwood.com/products/rotors/rotors.asp

To be fair though, here is the only article I could find in this short period to the contrary:
http://www.teamscr.com/rotors.htm
But one of his points about the F1 brakes is dismissed in the F1 article at the top. . .and then he goes back to say that "The one glaring exception here is in the rare situation where the rotors are so oversized"...

To each his/her own. . .but you gotta ask yourself, why would Brembo/Wilwood put their reputation, being the #1,#2 performance brake companies in the world, on the line? Their test support the use of drilled or slotted rotors, so do many others...

Robie

[B18a1CRX]

You make 1 lap at a timt the course being a mile long mx. Does you car get break fade that bad that quick. Or do you think cross drilled rotors will make you car slow faster?

[CT9A]

I've heard that the reasons that cross-drilled rotors crack are do to the fact that they're actually drilled with a press. When this happens, the drilling creates very small cracks and can compromise the integrity of the rotor. When these rotors heat up, the cracks increase in size.

I have also read that high end companies like Brembo and Wilwood don't drill their rotors. Instead, the rotors are actually cast with the holes already in them, as opposed to other companies just drilling OEM blanks.

If anyone wants, there was a very good thread with links to articles and research papers over on evolutionm.net. I'm too lazy to go find it.

[myshtern]

Ok, I think robie wins

Either way you are faster with drilled rotors. You have that nice weight reduction...

What do you guys have to say about slotted rotors?

[B18a1CRX]

When rotors are cross drilled they are done before the heat treating and hardening processes.

Don't cross drill your own they will crack and you do compromise the integrity of the rotor.

[chrisbarnett01]

Robie, go back and read those links you posted. Only one supports what you are saying, and it refers to outgassing of the pads, which is scientific fact to no longer occur, unless your pads are over 20-30 years old. Not one of the others support your theory. In fairness, most of them do not support mine either, they say nothing one way or the other.


Brembo and Wilwood, Stoptech, etc. Call them, ask if the holes and slots help with gasses, you'll get laughed at. The higher end brakes feature holes, and slots, for 3 reasons. First and foremost, rain. They help in the rain, no discussion needed there. Second, weight. Big brakes are HEAVY. Holes help offset that at a slight penalty to cooling, but most of the higher end systems have such advanced cooling designs anyways, its a mostly moot point. Third, looks. Aggressive looking brakes sell at faster rates than boring looking brakes.

You can link me all day to internet sites. I suggest calling someone such as Brembo's tech dept(very nice BTW), Wilwood(everyone there is great), Stoptech(never chatted with them, but heard they are A+++), etc. Even KVR, etc. Hawk, Carbotech, whoever.

Don't ask the guy at Autozone.

[myshtern]

Chris 1, Robie 1

[Weston]

The problem with most drilled AND slotted rotors is that there are so many holes and slots that there isn't much surface left for the pad to contact. In many cases this is because someone just took a slotted rotor and drilled holes in it... This is why you can find Brembo drilled and slotted rotors, even though Brembo doesn't make such a thing.

In addition to the reduced pad contact area problem, there is also the structure of the rotors that needs to be considered. Those little walls in the ventillated center section are also structural supports, so it's not a good thing to screw with that. In other words, it's very important where the holes are placed. Take a look at authentic Brembo drilled rotors... they have a rather unusual pattern, instead of the typical stylish pattern.

As for the benefits of properly drilled or slotted rotors, here's what I think... I do believe that drilled rotors improve cooling, and there is evidence to support this. And although I don't think there are many gasses that get trapped between the pad and rotor, I do know that there is loose pad and rotor material between them under hard braking during race use. My road racing pads came with a decent sized slot cut in the middle of them, but it was completely filled after racing on them. So, holes in the rotor would provide a place for loose pad and rotor material to escape to under hard braking. The holes also bite into the pads a bit, which is said to "clean" them of glaze (even though I've never had this problem with decent pads), and it might increase friction a little. However, it obviously decreases pad life, and I have my doubts about if the possibility of a little more friction makes up for the lost contact area.

Slotted rotors are pretty similar, but with a few differences. They aren't cut all the way through to the center, so they will be stronger, but that also has a down side... between rotor wear and material filling in the slots, the slots will become more and more shallow.

Of course, all of this applies to road racing use, which is dramatically different from hard braking on the street... You will not get your rotors anywhere near hot enough for it to matter on the street, nor will you have pad or rotor material wearing off so fast that it gets trapped between the pad and rotor. Race cars also use completely different pads, and it's normal for them to replace rotors and pads all the time anyway, so long life is not an issue at all.

Just because race cars use something doesn't mean that it's good for street cars. And drilled or slotted rotors are still only an option for road racing cars. There are plenty of people who run blank rotors with great results. So trust me, if blank rotors work on the road course, then there is absolutely no use for any "improvements" for the street.

If you want to improve your braking power or resistance to heat, then the place to start is the pads. I know they aren't bling bling like drilled and/or slotted rotors, but they will make a much bigger improvement than anything else. But just like rotors, there are crap "tuner" pads on the market too.

BTW, with freshly bled brake fluid, your stock brakes should be able to lock up the wheels (or go into ABS, if you have it)... that means that your car absolutely will not stop any faster unless you get tires that have more grip. Brakes don't really stop the car, tires do. If you lock up the wheels, then you lose approximately 30% of your grip and your braking distance increases. Grippier pads will only lock the tires up easier. This can be a problem at low speeds (ie you rear end someone in traffic), but they should give you better braking at higher speeds where the stock pads were less effective. If you get sticky tires to go along with the brake upgrade, then you'll stop better and more safely at all speeds.

[wild.irish]

I plan on doing some autocross and Kia brakes blow ass. I expect them completely overheat after something like 2 laps.
actually, aside from the technical discussion, a word of practical advice - go out with your current brakes. see how they really perform - it's a good experiment and a good feeling to be able to test your car to its limit. then, if you see that you are not satisfied with your stock brakes - replace them, drill them, whatever. if you are satisfied - you saved some time and money right there! ;)
the only reason i replace my rotors now is because i really cooked them several times in the mountains. but now i know what conditions may lead to this, and how it actually feels when your brakes are fried or getting dim, etc.

[Weston-work]

If your brakes are feeling weak, it's most likely because fluid boiled and/or the pads are glazed. Bleed the fluid and see if it gets better.

[wild.irish]

they're not weak now. just vibrating after some time of hard braking.

i was thinking, that boiling brake fluid just adds air into brake lines, which is compressed and it feels like your brake pedal is just going nowhere. what i had was same solid feeling in pedal, but it didn't give almost any results. so, it had to be pads. then i probably stopped at a light and held brakes while standing. so pads were pressed into hot rotor and left marks, which are now giving me this funny vibration whenever rotors become hot (expanding unevenly along the surface due to high temperature). there was a good article on this, i think it was your link, Weston.

[JL LGT]

This thread rocks! :cheers:

Keep the info coming, I may not be able to learn through osmosis....but I was learnd'ed how to reed in frrst graad!

I heard some good things about the Brembo blanks from a few people who use them when they run AutoX. But then again...my two cents isn't even worth half that on the street! ;NutKick;

[Weston-work]

wild.irish: Yup, if you have a solid feeling pedal but the brakes just aren't stopping you like they should, then that's usually a pad issue (ie it's overheated). When it happens to me, I can hear and feel the pad grinding against the rotor, but that feedback is dependant on the car's braking setup (boiling fluid and rubber lines tend to absorb it, but it depends on the pad too). Stock or stock replacement pads will smell pretty strongly and smoke a bit when they are too hot.

Warwick: Autocross really isn't very hard on brakes. It's just a tight course in a parking lot that is mostly about precision driving and car control; top speeds are only about 60 mph (briefly) and there usually isn't much hard braking. Even the cheapest AutoZone pads will hold up just fine; their coefficient of friction is just very non-performance.

[wild.irish]

Stock or stock replacement pads will smell pretty strongly and smoke a bit when they are too hot.
oh, how could i forgot to mention the smell! ;) of course they do smell when all that happens 'burnout: