cross drilled rotors???

Don't lots of high end cars come with them OEM? Like Porsche, maybe some 'Vettes, I think I've seen them on Lambo's etc. Just for bling? I see the logic and I'm not sold either, just askin...

Big difference in engineering between a $3000 set of brakes and a $150 set of rotors w/ stock calipers.

The exotic/semi-exotics have much bigger rotors to make of for the loss of surface area due to the drilling, too.

I guess a lot of it is bling, though.

The corner carvers thread explains a lot of it.

Some of you seem to be confusing autocrossing with track use. There is NO comparison when it comes to brake usage. Blingy rotors may be perfectly fine for 58 seconds of hard use at a time.

I finally looked at the corner carvers link, I have to beleave that this is one of the least BS car fourums

Lot's of people have tried and died at corner-carvers. If you post in the tech forums with speculation and no tech, you're gone. If you can't type anything other than fanboi txt message speak, you're gone. The members are held to a rigid standard. Outsiders look at it as some exclusive club of arrogant prix. Many of us find it to be an oasis from the relentless post-whore stupidity of most message boards. The one here is surprisingly self-policing also. Someone will now post how they got banned from c-c.com for some infraction they feel was unfair. Waaah. I've managed to survive there for years and have some strong opinions that at one point event got me a forced avatar, but I'm a big boy and can take it.

The good news for those who don't like confrontation or who simply just want to learn is you can read the forums at will without posting. There is a LOT of good tech there, and it's not limited to automotive stuff. I've been able to gain knowledge on everything from washing machines to water heaters using the search engine.

I'm not going to whine about it, but labelling me as a drifter fanboi, changing my user title to "Drifter" and banning me without any other notice all at the same time is silly on the face of it, especially if anyone knows me and my stance on drifting (not a huge fan of it). Has nothing to do with me being a 'big boy" about it or not. You may have survived there for years. I wasn't given the opportunity to even laugh off an insult and be a "big boy" about it.

No sweat off my nose, however, as there are other forums with tech and comeraderie, and less arrogant, hypocritical bullE36 M3. Like this one. ;)

To me, their action falls in the same category of the Ford Falcon forum that banned me with no warning when I posted, when asked, that besides my Falcon, I also have a same year Comet coupe and another Comet that was getting a Lexus engine. The message I ended up getting was that by mentioning the Comets and the Lexus engine going into the Comet, I had violated the rules of pure Falcon talk. Amazing.

Getting any kind of rotor other than solid ones is the very last thing I would ponder doing. AFTER, high end pads. AFTER, braided steel lines. AFTER rebuilding my calipers. AFTER switching to high end brake fluid.

http://www.tirerack.com/brakes/tech/techpage.jsp?techid=87 sez:

Brake Rotors and Track Use Slotted, drilled or dimpled rotors offered as OEM replacements should not be considered appropriate for high-speed track use. While grooved, drilled and slotted rotors offer an enhanced appearance and add some resistance to the boundary layer of gasses that can build up between the pad and rotor, they are not designed to withstand the extreme temperatures that are produced on the racetrack. If they are used on the track, it is very important that the rotors be carefully inspected and should not be driven on if even minor signs of deterioration are seen. Note, too, that if these products are used on the track they are not warrantable.

Their web page isn't making a lot of sense here. For example, looking at rotors for my Esprit, http://www.tirerack.com/brakes/results.jsp?autoMake=Toyota&autoModel=Celica+GTS&autoYear=1984&autoModClar=&brand=&category=Rotors

they start out with a link to the above quoted text, saying "don't track sloted/drilled rotors", then they show listings for the ATE premium one slotted rotors for "autocross/track." So, which is it? Use the solids only or are those ATE's OK for track use? Esprits like mine are brutal on front brakes.

I've read and re-read everything and I'm more lost now. I replaced the rotors on the P71 last summer with eBay specials (that were advertised as Brembo's, but I wasn't holding my breath) that were slotted/drilled/chamfered and zinc coated. They were wonderful on my HPDE and have been great under repeated daily driver use and autocrossing. I did keep the OEM rotors (they were fine) around "just in case". Now I don't know if the brakes were better because of the pad upgrade or the rotors or both? Should I take one off and inspect for cracks? Sigh

I put a set of Zimmerman drilled rotors on my wifes car because I think they are better when wet. As far as motorsports use goes I would guess it is a case of "you get what you pay for", walking around the paddoc at an ALMS race you will see many drilled rotors. But those also get inspected very often but there has to be some reason for their use.

But then again most, if not all, of the people here make me look like I know nothing about cars so I may be completely off base.

njansenv wrote: "I'd love to hear NissanLunatic explain how removing mass from a heat sink will make it dissapate heat more quickly..." You know, I laughed out loud when I read that. Take a block of aluminum, use it as a heat sink. Now machine that same block of aluminum and cut it such that you end up with fins/pins/whatever you can to increase the surface area. Now sit back and watch temperature drop faster with your drastically more efficient heat sink.

Yep. And rotors aren't really heat sinks, they are more like thermal storage devices. There is no way they will ever be able to reject heat as fast as they need to accept it.

The same debate has raged in the dirt bike world since the dawn of the dirt bike front disc brake in the '80's. The conventional wisdom is to use drilled rotors except in very muddy conditions. Then you should use solid rotors but be prepared for rotors that get hot enough to turn blue, boil brake fluid and squeal like crazy and I have seen that first hand. I always ran the drilled rotors that came stock, maybe I just didn't ride hard enough but I never had any problems.

I go with the 'it's more likely to crack' school of thought on drilled car rotors, though. Solid rotors will certainly get hot enough to warp and crack, though.

Another aspect of this: larger diameter rotors will be traveling through the caliper at a hgher speed than a smaller diameter piece. Higher speed = more heat generation.

But larger diameter rotors require less friction to generate the same torque at the hub. Less friction = less heat generation.

In the end, the car's forward energy gets converted into an amount of heat. The vast majority of that winds up in the rotors, unless you're just coasting down and losing the heat mainly to the tires (which dissipate heat nicely via ground contact). You can "fit" more heat into 20 pound rotors than 10 pound weaklings.

What I am referring to is that a point on the outside of a wheel has to cover a longer distance than a point near the inside in the same amount of time. If a pad is mounted, say, 4 inches from the center of the wheel 4 x 3.14 =12.56 inches per revolution. Now if the pad is moved to 10 inches from center 10 x 3.14 = 31.4 inches of rotor have traveled through the pads per revolution but it happens in the same amount of time. That means a lot of heat gets generated compared to the ones mounted closer to the center. Yeah, braking torque increases too. Like anything, it's a tradeoff: higher brake torque for more rapid brake heating. Check out the colors on the rotors on this 'perimeter brake' Buell.

Here are a couple of blue sky ideas for managing brake heat:

1) Liquid cooled rotors - Rotary unions in the hub/spindle allow circulation of coolant inside and through the rotors, back to finned coolers on the chassis. Infrared sensors watch the brakes, activating variable speed pumps on demand. (Alternative, make the rotors of friction material, and the pads of metal, then liquid cool the pads).

2) Hollow rotors that contain phase change materials (salts, metals). The heat of crystalization per unit weight is greater than simple bulk heating.When brakes are applied, the temp rises up to the melt temp. The temperature then stays constant until all of the material has melted, and only then resumes it's rise. After braking, the heat is dissipated back as the material cools and solidifies, releasing stored phase change heat energy. Basically a thermal reservoir system.

3) Nano technology rotor surfaces. One limiting factor is the surface area of the rotors. Internally vented rotors are one example of increasing the surface area to disipate more heat. Nano tech surface treatment can increase the surface area of internal venting 1000 fold (the challenge then is to vent enough air through) . BTW, this is already being done in the electronics industry to cool semiconductor chips.

4) Direct Liquid Nitrogen spray on demand onto the rotor surface. (Brute force deptartment).

Ok, OK, enough.

Carter

Also remember that the object is to generate heat, not to avoid generating heat. That energy has to go somewhere, and it has to go into heat, except for a Prius where it goes to heat and chemical energy. The bigger rotor will soak more calories of heat per degree increase in temp. When they get too hot, then the pads don't want to work right and you get fade.

Vented and slotted is the way to go...drilled are risky.

How are you getting the brakes to fade in an AutoX anyways? Mine are barely a little toasty after a run, far from fadey, and I have solid rotors on the front and drums on the back.

You have too small a car. My Monte Carlo could cook the front brakes coming out of the driveway.

First off, I too am a C-C.com member and have been for a few years now. Havent had a single problem, but I am a bit more of a reader then a poster over there.

I can sum up what needs to be kept in mind with brake rotors (if someone wants i can grab my materials book and provide formulas to back it up)

The brake system is designed to convert Kinetic energy into thermal energy.

A function of the effectiveness is the rate it can convert then dissipate said energy (make heat then shed heat)

As metal is heated, it expands. As it cools it contracts.

This creates thermal stresses, which is to say that the rotor is stressed by this expansion/contraction.

A hole in a surface creates a stress raiser, concentrating the stresses to a localized area. (meaning that it will fail EASIER with it there then if it werent)

Now, I dont have the testing data or anything to back up this hypothesis, BUT i firmly believe that much more transfer of the thermal energy will occur with properly ducting air through a center vented rotor then via the increase in surface area from drilling holes in it.

None of this is really a concern for street driving, only in a REALLY stressed setup for auto-x, and really applies on big tracks.

Anything CAN be overstressed thermally(as the picture below shows), Im just saying that the holes make it easier for a crack to form.

If you start having this happen, you need to start thinking about ducting. (as well as a proper cooldown lap when pulling off the track) (these are 12.9 inch mustang cobra rotors, got the pic from a CC.com thread)

And for those of you who may think it is only 'race' cars that can stress rotors to that point, the one on the left looks a lot like the ones removed from a completely stock F-body my friend tracked on a regular basis.

I also was able to develop spiderweb cracks in my Audi Coupe rotors after several weekends of use. About a thousand lbs less car. And these are good quality, solid center vented rotors.

Wally wrote: You have too small a car. My Monte Carlo could cook the front brakes coming out of the driveway.

Yowza, GM (like all the Big 3) WAYYYY downsized brakes starting in the '80's. For instance, I can fit 3 of the ThunderTerd's front brake pads on one hand and that car weighs about 3K pounds. We were seriously concerned about the ThunderTerd roasting the brakes during LeMons. Lots of the guys driving big Detroit iron (the Corporate Machine Corporation Caddy, for instance) had overheat related brake failures. IMHO it's more a function of a much smaller brake pad/caliper than the smaller rotors; a small pad/caliper doesn't have near the thermal capacity of a larger piece so it gets hot a lot faster and boils the brake fluid. Back when Speed still had the nards to show WRC, there was a tech bit about brakes and it appears many of those cars have liquid cooled calipers.

At least for the OEs the best compromise so far seems to be the internally vented rotor.

Cross-drilled refers only to the holes....

HOW the holes get there is another matter. I MAY be wrong on this, but the systems you see on Porsche and Ferrari for example... the rotors are formed that way. They don't start out as blanks, and then they go to town with a drill press.

Drilling holes puts stress on the rotor to start with, and then with abuse, gets even worse.

I just use Brembo blanks, and have had great luck with them. If powerslot made anything for my car, i would try them.

For autox I use a set of rotors that have about double the number of holes a cross drilled rotor usually has. I do this soley for weight savings. When the same car goes on the track, I put solid rotors on it since it took a while to drill all the holes and I don't want them to crack.

93celicaGT2 wrote: Cross-drilled refers only to the holes.... HOW the holes get there is another matter. I MAY be wrong on this, but the systems you see on Porsche and Ferrari for example... the rotors are formed that way. They don't start out as blanks, and then they go to town with a drill press. Drilling holes puts stress on the rotor to start with, and then with abuse, gets even worse. I just use Brembo blanks, and have had great luck with them. If powerslot made anything for my car, i would try them.

Corner-carvers has been over this one for awhile... http://corner-carvers.com/forums/showthread.php?t=21273&highlight=cross+drilled

Apexcarver wrote:

93celicaGT2 wrote: Cross-drilled refers only to the holes.... HOW the holes get there is another matter. I MAY be wrong on this, but the systems you see on Porsche and Ferrari for example... the rotors are formed that way. They don't start out as blanks, and then they go to town with a drill press. Drilling holes puts stress on the rotor to start with, and then with abuse, gets even worse. I just use Brembo blanks, and have had great luck with them. If powerslot made anything for my car, i would try them.

Corner-carvers has been over this one for awhile... http://corner-carvers.com/forums/showthread.php?t=21273&highlight=cross+drilled

Oh hrmmm....

Well, then, i believe i stand gladly corrected!

Then i guess my next question is.... why exactly do we not hear of Porsche rotors cracking? Better quality/metal more suited to the drilling without losing strength?

Great read, thanks for the link!