So are cross drilled rotors just for show?

"YSI-what can brown do for you" (ysi-what-can-brown-do-for-you) 02/16/2014 at 05:22 • Filed to: None

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I know they had them back in the day to let gasses escape from the surface of the rotor and pad. We now have pads that lower the amount of gas being produced substantially. I am having a hard time finding any sort of race car(now a days) with cross drilled rotors. They have slotted rotors, probably to get rid of some of the dust on the pads, but never any random holes.

YET, I see some road cars with cross drilled rotors. I am 99% sure they are they for show purposes rather than go purposes. Am I missing something here, is there any reason to still use cross drilled rotors still?

Tetrisaurus > YSI-what can brown do for you 02/16/2014 at 05:33

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Well yesterday's racecar tech is todays roadcar tech, so you just need to give it time and the road cars'll catch up

Squid > YSI-what can brown do for you 02/16/2014 at 05:44

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Just show, they provide too many avenues for failure on road cars that see so many heat cycles. The cheap cross drilled rotors like to crack and explode. . .

Pitchblende > YSI-what can brown do for you 02/16/2014 at 07:06

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As I understand it, drilling is used to increase the surface area to lose heat quicker. Modern racing brake discs are designed to be used hot, and do not work properly until you have heated them up. Road brakes have to be able to work from ambient temperate. You can drive for hours without touching the middle pedal on the highway and you still need them to work fully when that idiot slams on in front of you 200 miles down the road. So overheating is more of a problem, leading to brake fade if you track your road car, so cross-drilling can be beneficial, although in a lot of cases, yes, it is just posing.

Tentacle, Dutchman, drives French > YSI-what can brown do for you 02/16/2014 at 07:10

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You're not making this any easier if you compare steel rotors with ceramic rotors. Yet therein lies the answer.

Drilling in steel rotors, compared to slotting, is not such a great idea because every drilled hole is a potential starting point for fatigue cracking. This gets worse if glowing red to orange hot during operation comes into play. Those thermal cycles worsen things.

So why is it that all ceramic rotors are cross-drilled instead of slotted? It's because carbon/carbon composite (and carbon/silicon composite) isn't as susceptible to fatigue cracking as steel is. Given that slotting is a more difficult machining operation, especially on ceramic composite material, it makes sense to cross-drill ceramic rotors.

IDROVEAPICKUPTRUCK > YSI-what can brown do for you 02/16/2014 at 07:21

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Cross drilling is completely for show. Don't cross drill your rotors, you're making them worse.

BKRM3 > YSI-what can brown do for you 02/16/2014 at 08:13

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Drilled rotors are indeed a problem for track use - we M3 owners have a lot of experience with that. They work well and do cause less pad wear compared to slotted, but the issue is the cracking. If the cracks go from one hole to another or from a hole to the edge of the rotor, they're shot. If the rotors weren't drilled, all you'd have to look out for are cracks big enough to catch your fingernail on. So, although the E9x M3 doesn't "need" a front BBK, most people end up doing it in order to reduce running cost in the long term - the replacement OEM drilled rotors are $800 per front set. Ouch. The rears last forever though lol.

SnapUndersteer, Italian Spiderman > YSI-what can brown do for you 02/16/2014 at 11:41

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Cross drilled sucks for performance because it provides a stress concentration area where cracks are likely to form.

solid rotors or slotted ones are the way to go

911e46z06 > YSI-what can brown do for you 02/16/2014 at 12:55

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I almost died once when my brakes heated up on me in my e39, so I replaced the stock rotors with cross-drilled Brembos. It made a huge difference. Never had any sort of problem with the brakes heating up again. I always just assumed that the holes kept the rotors cooler.

YSI-what can brown do for you > Tentacle, Dutchman, drives French 02/16/2014 at 14:16

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That wasn't really the point, comparing steel and ceramics. I can go on Stoptech, Brembo, and Wilwood's website and buy a set of drilled rotors steel rotors, which is why I was wondering who the hell still buys them. The pictures were just that pictures.

Tentacle, Dutchman, drives French > YSI-what can brown do for you 02/16/2014 at 14:25

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Maybe I should have mentioned that I'm a Materials Science & Engineering guy, so to me the difference is very distinct and I know why drilling holes in one might not be the stupid idea it is compared to making holes in the other.

Any hole in a continuous surface means you've got a concentration of stresses. How a material handles those increased stresses depends on, well, the material. So steel is not as capable to manage holes as is composite ceramic material.

Cross drilled rotos might work in a street application, where temperatures generally don't get to the point of glowing. It's probably a poor idea if you go racing. Then again, if you have ceramic rotors, the point is moot, since that type of material behaves differently, so holes are no problem. In fact, they are prefereable over slots, because they are easier to make.

YSI-what can brown do for you > BKRM3 02/16/2014 at 14:27

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There was a student here with an E92 M3, his rotors were always wearing out and he didn't do much in the way of track use. The rotors on my car are 200 bucks for a set of good ones!! BBK for it though are 3 grand for the front :'(

YSI-what can brown do for you > 911e46z06 02/16/2014 at 14:29

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They might, although they do lower amount of area that allow heat to dispate through. I know that lots of times changing pads and fluid will really help brakes from dying on you and allow for better braking as well. That is what I will be doing soon. . . whenever that happens.

YSI-what can brown do for you > Squid 02/17/2014 at 04:28

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Some people buy big brake kits for their cars because it looks cool. . . figure that one out. Going cheap isn't bad if it is just for show.

Squid > YSI-what can brown do for you 02/17/2014 at 04:44

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Brakes are the one thing you shouldn't cheap out on in the quality department. Generally BBK's are at least $4-600 which keeps the showtards with no money away from them or they just get the front kit and greatly upset the balance of the car under braking and then wonder why they went ass first into a tree while they were on a canyon run. There have been quite a few instances where the crossdrilled rotors from china have exploded under heavy braking and caused serious damage. I don't mind buying cheap Centric rotors because I know that they have a decent reputation. I'd be hesitant to buy some cheap slotted and drilled rotors off ebay though.

Some people are fine with compromising safety, just look at all those kids who drive around with ridiculous camber and stretched tires. Just because it is fashionable doesn't mean it is worth the risk. I kind of wish the slotted and drilled rotors would go away. I thought they looked cool growing up but that was also when they reportedly had benefit for stopping faster, now that it has been disproven and we have some seriously great pads out there to use they are just utterly useless.

YSI-what can brown do for you > Squid 02/17/2014 at 05:05

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You say it keeps the show-tards(excellent word, I am totally using it) away, but I was on the NSX forums and they were debating on which kit looked the best(someone was looking to buy based on that). They went with Project Mu for its colors, even though it wasn't cross drilled. . . sometimes, I just wonder.

Wheels and brakes are two things you shouldn't cheap out on. Although if a wheel cracks you can limp the car to the side of the road. If the brakes go, well you better pray you stop in time.

Luckily, I am staying on stock rotors until they run their course(which won't be for a while). Changing the pads over the summer along with some nice fluid.

Squid > YSI-what can brown do for you 02/17/2014 at 05:39

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There are good blank rotors that are cost effective out there, and about 95% of drivers will never need the extra durability that buying a brembo fancy rotor may or may not afford. That being said there are always brand whores who don't care about end results and only want the stickers on the car.

Those NSX guys are right though... Project Mu has some sexy colors going on. . . But you won't see guys even thinking about the costs of getting Project Mu BBK's on your run of the mill "show car" the NSX is in a league of its own and as long as you don't fuck it up terribly it is one of the few cars out there bound to appreciate. Plus everything is expensive for them.

You are welcome to use "showtard" anytime you like. It is my gift to Oppodom. . . Use it wisely.

puddler > Tentacle, Dutchman, drives French 02/17/2014 at 14:07

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weight reduction.

Tentacle, Dutchman, drives French > puddler 02/17/2014 at 14:13

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That's not just for weight reduction, that's also for " Get this crud/sand/water/mud off my All terrain Bike (or endurance bike) brake rotors!"

Because if it'd be solely for weight reduction, they'd have used smaller diameter rotors.

YSI-what can brown do for you > Squid 02/17/2014 at 17:07

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I don't really track my car just cause it costs so much to do in the first place, so I don't need slotted 13" rotors on my car. However, when I do decide to finally make a track car out of college, everything will be overkill!

I am going to get their pads for my car over the summer. They will be bright blue and no one will see them cause they will be covered by the caliper and by dust. lololololol

Squid > YSI-what can brown do for you 02/17/2014 at 17:44

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When you change your pads out check and see if Project Mu pads need to be bedded in on rotors with a clean surface to get that pad compounds transfer layer down. If you just slap the pads in the transfer layers may not be compatible and you'll have shitty brakes.

YSI-what can brown do for you > Squid 02/17/2014 at 18:47

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I will, these pads are more for beginners, so it shouldn't be anything out of the ordinary for bedding. I think the few people I have talked to did theirs normally.

Squid > YSI-what can brown do for you 02/17/2014 at 19:17

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The only thing to worry about is a clean rotor surface. but bedding in pads at night is pretty sweet when you can see the sparks and the rotors get red hot.