The drilling causes damage to the structural integrity (so to speak) of the rotor and will make them crack much easier.

 

I just got back from VIR yesterday. I have been there over 10 times. I am not the fastest driver and I have never . . . and I mean never, ever, not even close, been even threatened by a miata, stock, raced prepped or whatever. Don't see why you should. It blows me away when I see them run off track cause I don't see how they get enough speed to do it. You should upgrade your fluid and pads and you will be fine.

As for the drilled/slotted debate, if you look at what people who pay for their own stuff bring to the track, it is mostly stock rotors. Some run the slotted as it does help in braking, but it also eats thru pads quickly. That being said, I run the drilled/slotted when I am on the street, but at the track, I switch to stock rotors I buy from people switching to d/s.

BTW - VIR is an awesome track, you should start running there whenever possible. Good Luck.

 

I actually ran OCAutosports cross-drilled and slotted rotors (with Hawk HP+ pads) at a track day @ Pueblo Motorsports Park a few weeks ago. It was very hot that day and I was really pushing the car. Overall I probably did about 40 laps over the course of an 8 hour day and I did not have any problems with my brake setup (no fading), other than turning the paint on my front 4-piston Brembo (stock) calipers from silver to gold by the end of the day. I actually put on these rotors for the car show circuit, and never intended to use them on the track, but I got lazy, didn't want to change them out, and used them anyway with great results. Now, those results might be different if I press my luck and try to use these rotors on multiple track days. It would only be a matter of time until they just can't take any more heat cycles and finally crack, I won't kid myself into thinking that won't happen. I will be changing back to stock Brembo rotors with new HP+ pads for any future track days.

After that longwinded paragraph, I want to answer your question about why all of the high-dollar exotics run cross-drilled rotors and don't seem to have problems. Most likely, those rotors are so expensive that they were actually cast with the holes in them. They did not start out as blanks and then had the holes drilled, which significantly weakens the area around the holes, hence the heat cracking that extends from the drill holes radially. Those expensive rotors, with the holes cast in them from the start, can reduce rotating mass at the wheels, which can have a big impact on how much horsepower is getting put to the ground, handling, braking, etc. All the things that exotics must do well.

It was touched on before, but I believe that a lot of racecars run the drilled and slotted (or slotted only) because each individual rotor will only last for a certain amount of laps (or 1 race - depending on the length) and will be thrown away before any of those cracking problems would typically ever occur. And they probably get those rotors from a very high quality source to ensure that the metal is up to the task of absorbing massive amounts of heat (through friction) time after time.

I hope this helps. Just so you know, I am no expert on street cars or racecars, I have just done a lot of reading and researching on the subject and I am a Civil Engineer so I have at least a rudimentary knowledge of physics, heat transfer, mechanics of materials, etc. which all play into high performance braking.

 

Well, the drilling has ZERO benefit, so why even take the risk?

 

Most every road race car will use slotted rotors. VERY few today use a drilled rotor.

Slotting helps clear dust away and can lessen the grooving and scoring that happens when dirt and dust get embedded in a pad, I have see the improvement directly. The other thing is race cars generally build much more brake temperature than street cars do. And big cars like IndyCars, ALMS, Grand-Am cars don't have power brakes. The slotting helps to get rid of the gas layer that can build @ 1000 degrees and act as a buffer between the pad and rotor. Slotting helps get the gases out. If you have power brakes, you have a much easier time getting through that gas.

The toughest rotors I've found for stock sized LS1 brakes are the Racing Brake stuff. I picked them up because they are the most durable and run the coolest for track use. In fact the Racing Brake fronts use convergent, and directional vanes on the front... the only LS1 rotor that does. They are also made of a metal composition that is a lot tougher than street rotors. And fwiw, they also cost more because it requires more tooling because they are making two different rotors, one for each side where others cheap out and make one rotor that works for both sides (like GM). That's fine for street use, even some fairly hard street use--but not ideal when you are really pounding on the brakes like at a track day.

 

Well...if you had read the post above yours , you would have seen that the reason drilled rotors exist, and especially on expensive exotic cars, is two-fold. One, they look cool, and two (the bigger reason) they actually make the rotor lighter, therefore reducing unsprung (or rotational mass). Even to shave 1 pound total off of the 4 rotors is something that exotic car manufacturers like to do. That may seem trivial to a layperson, but even small amounts of weight being removed from the wheel, caliper, caliper bolts, rotors, etc. have a relatively big increase in performance over say...changing the front seats to lighter racing seats and saving 80 lbs from the sprung weight of the car.

I believe that this is the same reason that the highest dollar brakes out there utilize ceramic rotors because they are much lighter (see above about lowering rotating mass) and have a superior ability to dissipate high amounts of heat.

By the way, I do agree with you as far as not taking that risk in track applications, but street cars (albeit highend ones) were also brought into the mix, and d/s rotors can perform great on the street.

Also something I just thought of, is I have seen an awful lot of late model Porsches that have those drilled-only rotors and I am betting that those are the types that are cast with the holes in them. I don't know about everybody's experience, but every time I have ever been to a track day I have seen some type of Porsche. And I think that a majority of guys that own Porsches like to track them, and I have never heard of their rotors cracking, warping, or breaking while on the track, so apparently Porsche has the whole drilled thing figured out.

 

not to mention, many of the very high end exotics now have carbon fiber rotors. holes or no holes, you cant compare CF to a regular iron rotor.

 

I have a prepped Autocross car. 1994 Formula. It's taken a LOT to get it to run with a stock Miata on a tight course. On an open course with some breathing room I suck them in but they can sometimes still have an advantage in certain locations and will make up the room. I will tell you however that TIRES make a huge difference and without knowing all the details of both cars its hard to judge. Miata's are pretty damn sweet when it comes to a road racing car. They are cheap to mod and race unlike my F-body which is costing a mint. BTW: A Z06 would certainly have NO issues with a stock Miata in any circumstances.

 

A couple of things.

First of all, NO ONE drills holes to "lighten" a brake rotor. You want the biggest, heaviest rotor that will stop the car. All that mass absorbs heat, which yields better braking. However, once you have a rotor that's big enough, you want all that mass as close to the hub as possible. My point here is that, why drill holes, which remove mass near the hub but leave it out near the wheel, when you could make the rotor smaller in diameter, have the same braking performance, but reduce moments of interia?

Second, yes, drilled crack a little worse than cast holes. But, all holes crack. Why? Because that are of the rotor will cool faster than the undrilled parts next to it. As it cools, it shrinks. As it shrinks, it pulls away from the surrounding metal. If that force is stronger than the forces holding the metal together, a crack will form.

Lastly, some real-world experience. I have 14" Baer 2-piece rotors, with stock-style Corvette calipers. When I bought the brakes, they came with slotted and drilled rotors. They were fine for braking. However, after only 3 race (20 minutes apiece) the cracks at the holes had grown from imperceptable to connecting holes and extending to the edge of the rotor.

Now, I have baer blanks. They've lasted 6 races, and look brand new. Braking performance is roughly the same. But, at $200 per rotor, it's a helluva lot cheaper!

 

fortunately this track favors HP...BUT, the corners are slow and difficult. For a first timer like I believe you would (I may be wrong..) be, I bet a "Pro" Miata driver could easily keep pace with you and with real race experience get by you no problem...not to say you may not be able to catch up with him on the straights, but it all depends on how quickly you learn and catch on. The race track is no place to be a hero when you are beginner, that gets you into trouble.

Now, what kind of "Pro" are we talking here? Does he have a full paid ride with sponsors and a team that covers ALL of his expenses and he makes $$ off it, or is he a "Pro" driver who has a couple/few sponsors who help out on tires or brake pads or race entries and a team of him and a couple friends and is still out $$ at the end of weekend?

Because there are 2 different level of "Pro" drivers out there, those who can afford to be called a "Pro", and those who are that talented of drivers..

 

oh, and depending on driving styles/braking habits and setups....more specifically stock rotors, inadequate cooling, stock calipers, and race pads; slotted rotors can help resurface the pads helping to prevent the over-heating and thus creating pad glazing during a session.

Ask how I know this... :o

 

I disagree, car manufacturers do market the drilled rotors as more performance with less weight. Also the mass of a rotor has nothing to do with the heat dissipating abilities of said rotor. The surface contact of the brake pad on the rotor surface is what determines the loss of forward momentum via friction heat losses. Why would highly paid, extremely intelligent design engineers use the very light ceramic or even carbon fiber rotors (look it up to believe it, I did) on a supercar or racecar? Obviously by your logic they wouldn't work for crap because that aren't the "biggest, heaviest rotors" you could fit under the wheels...which is not true at all. I dare you to go out and find a couple of 100 lb rotors and bolt those up to your car (it must work better because it has so much mass...) and see if your braking performance increases or decreases. Good braking also has to do with how much weight (mass x gravity) you are stopping, and in the case of rotational mass, every little bit saved really helps.

As for your argument about the area of the rotor near the holes cracking because it cools faster, I agree with you that it does cool faster by a small amount, but I don't think that is enough to make a rotor (with pre-cast holes) break. Again, by your logic, why wouldn't the extreme outside edge of all rotors crack and "pull away" from the other metal because that particular area cools slightly faster than the rest of the rotor. It doesn't happen...

The cracking around the holes of all rotors that have been drilled after the fact is from the stresses put on the metal through the drilling process, which are then exacerbated during the repeated heating and cooling process when used on the track.

 

Wow, lots of good info here! Thanks for the insight guys! Hopefully it will help me out pretty soon. I'm also heading to VIR to turn some laps. I'm gonna have an instructor with me though. I'm pretty confident in my driving, but it never hurts to have a pro show you the ropes!

 

People who are trying to sell a product will "market" them in whatever way they think will sell the most product. Just because they say something doesn't mean that it's true.

Of course it does. What takes longer to heat up if you use a cigarette lighter - a paperclip or a steel I-beam? A lighter rotor will heat up faster, and therefore heat up more. Therefore, it will hit a higher heat point, which is likely to exceed the rating of the pads used.

Now, it is true that a lighter rotor will also cool faster. But, if you've already glazed your pads because you exceeded their heat range, then what's the point?

You can't compare "why/how" a ceramic/CF rotor works to "why/how" a ferrous-metal rotor works. An iron rotor with regular pads works by combining 2 methods to stop the car - converting momentum to heat and friction. That's why you get brake dust, you have to replace race pads every few races, and have to get new rotors. But, ceramic/CF rotors don't use the "friction" part of that. Movit brakes has a ceramic rotor/pad combo that has been on their dyno for years now, and has logged a few hundred thousand miles of simulated racetrack driving. They are still on the original pad and rotor. They simply don't wear out.

Sure, let's take it to extremes - that's a valid arguement.

Notice I said "biggest, heaviest that will stop the car"? Once your brakes will stop the car like you want, then there is no reason to get bigger/heavier brakes. That limit is usually found by when your tires lockup. Once you ahve locked up the tires, there is no reason to have better brakes. If there is no reason to have better brakes, then there is no reason to have heavier brakes.


Ummm - because it's a circle. As the outside of the rotor cools, it tries to get smaller. This means that it actually draws CLOSER to the metal on the inside of the rotor.

Cast holes still crack. Perhaps not as rapidly, but they still crack. Check out the following:

So, unless you have the funds to buy new rotors after every or every other race, then you should get slotted or blank rotors.

Of course, if you have the money to buy new rotors and pads after every race ($200/rotor, $300 for front pads = $700/race), then you should probably spend $9k on a set of ceramic brakes. It'll be worth it in terms of performancea AND economics.

 

By the way, I appreciate a good-natured argument. This stuff fascinates me and I always appreciate the chance to learn more about it.

 

And I think the point YOU are missing is that while they may in fact perform better, you are assuming ...

... they are made from the same material as teh $100 rotors available from rotorsRus.com
... owners routinely run them on the track and then drive them to work the next day
... because a wing on a McClaren "works", a wing on a Civic must work also because its a wing
... the rotors will last 60K miles, not just a 1 hour race.

 

w00t!

Yeah - it's tough to know what's good and what's bad, when a lot of marketing says something is good, and only users are saying it's bad.

 

Silverbeast,

In stead of coming here & yappin' about it, why not go out & see? Stock Miata's can be rented & I'm sure that there will be pro's @ the track who will put seat time in one for the test. In a 10 lap race (time trial), I'd give it to the pro in the stock Miata. You didn't mention how many laps & also didn't mention that you'd be in here learning how to set up your car before the race. Sounds like your friend offered the statement as "stock Miata" against "your car as it sat in the parking lot on that day." In any event, an inexperienced road course driver over 10 laps against a pro in a lesser car = Pro FTW.

One lap, you might have a chance.

 

Our track here is similar. They use the 1/4 as the straight. ~1/2 mile. I used to have a supercharged miata, with a whopping 130 gteched hp! I could get upto 160kph (Canadian) at the end of the straight. With a srt4/audiS4/subaru 265 I can get up to 200kph at the end of the straight. Buddy who is an awesome driver in a 190 hp M3 can lap as fast as 911 turbo's. Sorry, but the mustangs (saleens, rousch's) are all able to be passed with good drivers with average cars (haven't seen any firebirds/camaro's out there). Trouble is, miatas are freaking gutless. I could do magic on slow corners, but that track is not a low hp track. It wouldn't be close, like I bet 2-3 car lengths or more per lap.

C5/6 vs a miata. 10 seconds or more.

Which is why I am looking for a LSx powered bmw.

I bet a rookie could keep Shumacher (SP?) in a stock miata at bay on that track. However, based on our track, your stock brakes would be done after 3 laps (ask me how I know), so the miata would eventually win, depending on length of laps. Rookies tend to use way more brakes than normal, as they (used to be me too) over brake, and have less body control (adversly affecting braking/speeds/etc) using the tires/engine to brake. I went through 2 sets in the audi in 3 track events. 3800lbs and 340hp is not a good road racing receipie.

In my almost stock 09 subaru 265, I double lapped a girl in a 20 minute session in a mazda speed miata, and a guy in a gutless one (199x). My laps times are about 90 seconds. Faster guys are 85, super fast are 80 seconds. 20 seconds a lap is huge.

Summary, I would be a ton of money on you, but there is no way to find out, but race him. Take a class, practice being smooth, your car will appreciate it. Don't try to beat everything in site. Steady, consistent movements, not herky jerky will get you around fast.

 

Well that would quantifiable data to make a point which seldom works on internet forums.

I mean come on ... who ever heard of backing up opinions with data any way.