More on drilled vs. slotted rotors
 

More facts about rotors. May the great myth of drilling rotors for improved cooling finally die...

Darrick Dong; Director of Motorsports at Performance Friction.

"In the days of asbestos pads there was a gas boundary layer that appeared at the interface area of the pad and rotor. Although that gas boundary layer still occurs it is much less of a problem with modern friction materials. Slots are more than adequate to carry that gas away. Years ago that gas boundary, along with reducing weight, led to the popularity of drilled rotors. However, in the intervening period, the myth has persisted that cooling is the main reason for drilled rotors. Anyone that tells you that drilling makes the disc run cooler is smoking crack."

Why is Dong so adamant? Because he works with racing brake systems for a living and it isn't too hard to take two identical rotors, drill one of them and slot the other, put them on a brake dyno and measure temps and life.

Good stuff Damon!

Good info!

woo-hoo!

ok, now I shouldn't have to hand out so many idiot badges

I can just point at the drilled rotors

What's your take on dimpled/slotted rotors

Thats good info Damon ............ unless he isn't too bright, and is messing with us.

That would make him "Dick Ding Dong"

Sorry for the horrible joke, but I couldn't resist :eek:

Still waiting for someone to bring up the mythical rotors with the holes cast into them... ;)

Doesn't help keep them cool...but the holes do help them look cool. They will never go away because of that. Show and street cars will still have them. Can't call them stupid, just fashionable. :p: Have you seen those starflake shaped rotors with most of the non-swept area removed to look pretty?
:gotrice:

just wondering since he has access to do so, how come noone has ever posted results of the brake dyno? it seems everyone wants to downgrade drilled rotors, yet they never provide factual proof. i can understand the theories behind it, but i'd like to see evidence. if it wasn't worth doing, brembo and many other companies wouldn't still be doing it

Those are called scalloped rotors. The only reason why they are like that is for weight reduction. what do u mean by 'non-swept' area?

Since so many people think drilled rotors are better or just plain look good they will always be able to buy them. Companies are in business to sell products. It's the customer's responsibility to determine if the product actually adds peformance to the car. I'm still suprised by the number of "mods" everyone trumpets that are completely useless IMO.

I've seen a lot of pictures of crossdrilled rotors that cracked during track use. I've never seen a single picture of a plain or slotted rotor that cracked.

Crossdrilling is fine for the street, especially if the edges of the holes are rounded to prevent stress risers (and eventually cracks) from forming, but anyone who thinks that it's anything more than an appearance mod needs to do some research.

Of course they would, because they can charge a premium for it. People think it looks good, and most of them don't know or don't care that there's no performance benefit. Most people don't track their cars anyway.

Damon, I didn't see anything about "bling" mentioned in your post. :)

thanks for that post but drilled looks better and slots make a fluttering noise when you brake

News to me. You going by what you think or what you know?

i'm sorry, but without any hardcore proof, it's hard to just believe someone's opinion. like i said, brembo has been doing it for years and is ovbiously going to continue doing so. a company with race heritage isn't going to care about looks versus performance. granted, i've seen cheap ass ebay rotors crack, but nothing of quality. hell, i've seen solid rotors crack before, does that mean they're junk?

Actually, those drilled rotors you see aren't drilled by Brembo. Brembo sells the solid rotors and aftermarket companies drill them and then sell them under the Brembo name.

It's not opinion, it's fact. If you spent a few minutes researching brakes, you would discover that. As Mahjik pointed out, the rotors you see for sale aren't drilled by Brembo. In any case, Brembo is hardly the be all-end all of braking. I find their kits both overpriced and overweight. AP and Stoptech make better, lighter products for less money.

You understand the difference between fact and opinion? Drilled rotors exist because people think they look cool. As long as there is such a buyer there will be companys who sell drilled rotors.

If you don't believe the guy who works for one of the most preiminent brake companys in the world maybe you'll believe the real racers who race all over the world. Nobody in the modern world who uses iron brake rotors (F1 before carbon, CART, IRL, NASCAR, ALMS, WRC, TransAm, Formula Atlantic, F3000 etc) uses drilled rotors. Why? Because in racing it's performance that counts, not looks.

You guys keep your drilled rotors and the rest of us will just keep outbraking you late in the race :cool:

No. It means the brakes were undersized for the application or abused. Anything will fail if used improperly.

Here's some more rotor info here

it seems some people are so in love with the look of drilled rotors, they wont believe its useless.

I'm struggling to beleive this....Sorry for the gigantic picture but BEHOLD! The Ferrari Enzo....
If they don't know about brakes...who does?

http://www.supercars.net/servlets/PW...eNoM/1car3.jpg

That looks like a carbon rotor to me, which is a different ball game. Also some companies like Porsche that have rotors with holes in them are not drilled but are cast with the holes already in them. (Or so I have heard) This means the integrity of the metal isn't weakened as much.

I'm no expert on the subject but I know what I have seen over the years and that is cracked rotors that were drilled. Hell, I saw another set two days ago.

Those are ceramic brakes and they are 15" rotors. If we used 15" drilled rotors on our FDs, they probably wouldn't crack either....

Porsche does it for looks. Anyone who believes different is giving Porsche too much credit.

The Enzo has carbon brakes, not iron brakes. Different set of rules apply.

As for Porsche casting the holes into the rotor: Casting the hole is a slight improvement over drilling the hole but still forms a concentrated area of stress. At the same time holes mean having less mass in the rotor and therefore less thermal ability while offering no increase in rotor cooling performance. Since the cast in holes still concentrate stress around the edges of the holes the rotor will at the very least have a shorter lifespan than a non-drilled rotor; most likely the holed rotor will have less performance too. This is true whether the holes are machined or cast.

I have not been able to verify that Porsche in fact casts the rotors with holes in them; I find that hard to believe. It's very easy to prove though: Examine the inside edges of the holes closely. If they have a shiny and smooth surface they were machined. If you can make out surface porosity from the casting they were in fact cast in place. I haven't wanted to appear rude and peer closely at anyone's Porsche brakes in the parking lot :p: From now on whenever I come across a Porsche in the paddock with the wheels off I am going to stick my head in there. I'll let you know what I find...

Woops...sorry about that guys. Wasn't aware that there were different rules for different materials. More or less I'm a beleiver in what you guys say. It just bothers me then that companies like Porsche and Mercedes use drilled rotors for looks....