I need ROTORS: Slotted vs. Drilled vs. OEM ?????

Assuming you've done your homework, this is great information jpr!

Originally Posted by GunMoto

Assuming you've done your homework, this is great information jpr!

Thanks - you can rest assured I've done the homework, but being human I won't rule out the possibility of one or more dumb mistakes. So if you ever run across any contradictory info, please post it and add to the knowledge base.

A few more -
* Powerstop (Autospecialty/TRW) - holes are drilled, not cast
* ATE - does not offer perforated rotors, only slotted
* Powerslot - does not offer perforated rotors, only slotted
* Frozen Rotors - holes are drilled, not cast
* EBC - has drilled dimples, no perforated rotors
* BALO - does not offer perforated rotors
* FTE - does not offer perforated rotors

I'm now totally convinced the BMW Motorsports rotors made by SHW have drilled not cast perforations.

On their website - http://www.shw.de/index.php?58 - you can find this photo of the actual machine they use to drill the holes. The caption of the photo translates as "Perforation machine for quantity production - qualitatively high-quality and economical"


The remainder of the text on the page is this - (bold mine)

Special solutions for brake disks: Individually to High ending in series-evenly the quantity production of raw and worked on quality brake disks SHW of automotives offers by know-how of many years also individual special solutions, in order to become fair the rising requirements at lightweight construction, security, optics and comfort. The associated development projection/lead benefits all our customers, since appropriate experiences will transfer to development and finishing techniques in mass production are can exemplary here the group brake disk developed by SHW of automotives, which connects extreme maximum stress with highest security. Here the grey cast iron friction ring is connected by steel pins with the aluminum pot and can expand when high heating up freely. A precision part, on that hardly a High end Fahrzeughersteller, hardly a sport or a rennsportwagen do without through brake disks do not only know appropriate manufacturing plants worked on and geometisiert, butby the integration by perforation drillings, Duppen or slots to be also further refined. This serves not only the rising optical requirements, but also the purposeful optimization or as wear indicator

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Additonally, there are several photos of castings and molds on their website, none of which have any indication of them casting rotors with perforations in the disk.

Basically, if casting rather than drilling holes in the rotor face were easy, common, possible, and/or technologically advantageous, manufacturers would be both doing it and bragging about it. It should be easy as pie to confirm that somebody is making rotors in that fashion rather than impossible.

excellent detective's work JPR

Originally Posted by jpr

Thanks - you can rest assured I've done the homework, but being human I won't rule out the possibility of one or more dumb mistakes. So if you ever run across any contradictory info, please post it and add to the knowledge base.

Haha sometimes I think all JPR does is homework

But he is fair and if you put out the information he will definitely listen to it.

Looks like a stalemate in the actual info on the casting. I personally dont like drilled rotors at all cast or otherwise.

If either of you could find the information on casting I would love to read it. I will try to look as well.

The way I see it, if nothing else I figure the burden of proof is upon the claim that a particular (or any) rotor is cast with perforations in the disc face. So far all the available evidence shows that they are drilled. While you can't truly prove a negative, the scientific method says that the best theory is that all perforated rotors are drilled until somebody can provide a documented example of one that isn't.

In the big picture though, it really is just trivia. All rotors are not of equal quality, be they plain, slotted, or drilled. I have no problems with anybody choosing to go the drilled route, I just think it's a good idea to be aware of what you are gaining (less wieght) and what you are losing (increased risk of rotor failure) and every big kid can make their own choice.

Bottom line is that it is always a good idea to buy quality rotors. If you want drilled rotors it is especially critical to get the best quality possible.

The SHW manufactured BMW Motorsports rotors, such as UUC offers, are one of the good safe choices, no matter how they are made.

Some more info found on another forum posted by a guy who works for Brembo -

However, one intersting item is that all of our X-drilled holes are exactly that....drilled.....even the Porsche ones. Its a bit of an urban legend that Porsche "casts-in their holes" for strength. Truth is, when I started with Brembo I thought the same thing. I mentioned it to our Italian resident Applications Engineer. I was kinda surprised myself. He laughed and added, "People seriously think we cast in all of the holes? Wow, I'd love to see the mold for that! No, actually they are all drilled and chamfered post-casting. "

spoke with one of the Apps Engineers from Italy and he confimred what was said. The rotors are designed by Porsche and cast/machined by SHW. Brembo supplies the Caliper and the knuckle, and assembles the wheel end (thus the reason for the wheel end assy on my desk).

He said that in the case of Porsche, even the caliper is a build to print. In other words, Porsche Engineering designs all of the components, but has manufactuing done by SHW and Brembo.

He also added a few comments/corrections on the rotor design itself. The "half-vanes" are there soley for preventing crack propagation. The holes are not actualy through the vanes (something we verified with a paper clip with the one on my desk). The holes follow the same curve as the vanes and are placed extremely close to the vanes, but don't actually go through the vane itself. Finally, he added that even SHW does not cast the holes in, they are indeed machined and chamfered. he said he is not aware of anyone who manufactures cast-cross-drilled rotors on a mass-production level.

And in response to the question - "what is your opinion on X Drilling of rotors?"

My personal opinion is with today's materials its mostly for bling. there are some slight benifits to it, but there are also some negatives. There have been Brembo/Porsche tests to show that x-drilled rotors increases first effectiveness in wet conditions. Assuming there is enough mass for thermal capacity of the application, X-drilling can save a slight amount of weight (although any unsprung, rotating mass savings help) and offer small increases in cooling speed. However, they are prone to crack more, especially propagating from the drilled holes. This can be accounted for with a proper rotor design (i.e., pillar and hole location/orientation) to prevent small cracks from propagating all the way to the disc edge. If the rotor is designed correctly and sized properly for the application cracking is minimal. That being said, many designs on the market (I won't name any specifically) arent designed properly (arrangement to prevent crack propagation), machined properly (poor or no chamfering), and are under-sized for the application (thermal mass). This is especially true of those popular in the ***** community.

Now, with all of the previous being my personal/professional opinion, Brembo understands that there are both advantages and disadvantages to X-drilled rotors. We leave it to our customers discretion as to which is used (drilled/slotted/solid-faced). In most OEM situations, it comes down to Marketablility.

Good stuff jpr!

Just to keep adding to the knowledge - from all the research I've done, if you want to get drilled rotors look for two things as indicators of good quality.

First, it is critical that the holes are chamfered (beveled). This reduced the stress riser effect and will help to mitigate cracking. It's also a good indicator that more thought and effort has gone in to it than simply "Me make hole."

Second, it is preferable that the drilling is done by the manufacturer of the rotor. This ensures that the rotor was originally designed to be drilled one and has the appropiate structural and metalurgical properties.

So we seem to have agreed, based upon the data here, that drilled rotors will fail before a flat disk rotor of more or less equal quality.

The question is, can I do drilled rotors, purely for looks, and drive safely down to starbuk's without having the disk explode unexpectedly some morning causing me to spill my grande latte all over my myrtle trim ?

Depends - is your myrtle trim drilled, slotted or plain?

Originally Posted by Rob Levinson * UUC Motorwerks

:Customers ask for purple paint, too, and any auto maker is happy to oblige to make a sale.

Exellent example!

Great work JPR, great thread on the myth of the drilled/cast rotors. Disadvantage of the drilled rotors is that they also eat up your brake pads quicker. Go with slotted or a blank is my personal recommendation.

wow.. now i dunno what to get cuz i need rotors too. I definitely want slotted, but i dont know which brand. I can't afford brembos so that's out. i need something with good quality and excellent price?

If the budget is tight, I'd recommend skipping the slotted rotors and spending a little bit more on upgrading the pads. Slotted rotors seem to run at about a 25% to 100% premium over just the solid rotors - which works out to spending about $50 to $200 extra. Performance wise, you'll get a lot more bang for the buck spending some or all of that on pads.

what is better than hawk pads? and what kind of pads should i get for street use and a lot of highway driving. ??? thanks for the info jpr

Originally Posted by FLPSIDE

what is better than hawk pads? and what kind of pads should i get for street use and a lot of highway driving. ??? thanks for the info jpr

Can't help you much there - I've only replaced my brake pads once and am using the OEM pads. But there's some good info to be found here - http://www.zeckhausen.com/BMW/E46_M3.htm - plus, of course, several threads on the subject.

thanks jpr!

Check Ebay. Zimmermann solid rotors are very good and relatively cheap.