Blue Batmobile

iTrader: (22)

Help me decide which style I should go with. Advantages, disadvantages...

Bat™

DrCold

Well, I've heard they they aren't the best for performance, but slotted and drilled rotors are DAAAAMMMN sexy!

D@ActiveTuning

iTrader: (17)

Agreed, slotted is usually the best for performance though. Crossdrilled runs the risk of some cracking.

westpak

iTrader: (19)

It depends on what you are going to do, the xdrilled might crack but probably only if you do some heavy braking like a track event, street driving you should be fine if you get good quality ones like DB and some backshop drilled ones.

I have the DBA's and they look great but actually wont use them for my next track event instead I will sacrafice the stock rotors as they are cheaper.

Blue Batmobile

iTrader: (22)

I don't plan on any major track events. I really like the look of cross drilled rotors.

Bat™

mofoz

iTrader: (1)

slot definetly performs better but those cross drilled are oh so sexy.

failsafe

From a Stop Tech whitepaper:

For many years most racing rotors were drilled. There were two reasons - the holes gave the "fireband" boundary layer of gasses and particulate matter someplace to go and the edges of the holes gave the pad a better "bite".
Unfortunately the drilled holes also reduced the thermal capacity of the discs and served as very effective "stress raisers" significantly decreasing disc life. Improvements in friction materials have pretty much made the drilled rotor a thing of the past in racing. Most racing rotors currently feature a series of tangential slots or channels that serve the same purpose without the attendant disadvantages.

But I'd say go with what you like since your rotors won't see the additional stress of the track.

apsilon

If you plan on any track events at all go with the slotted. I've seen even quality cross drilled ones crack after half a day at a drive day.

Blue Batmobile

iTrader: (22)

I'm going with slotted cross drilled rotors, a nice compromise.

Bat™

Asterix

I've seen this whitepaper quoted on other forums, and I have several problems with it. Yes, holes are stress raisers, but so are slots. So are grooves. If you look here: https://my350z.com/forum/showthread....threadid=67568 you'll see that rotors can crack even without holes or slots. That's a problem with cast iron in general.

If the edges of the holes bite into the pads, so would edges of slots and grooves. If the edges of the holes bit into the pads, you'd think the pads would get scraped away in no time. My pads last for years and many miles. The "bite" arises from the pad rubbing on the rotor because it's not riding on a high-pressure and hot film of gas, not because the edges of the holes are scraping the pads. Besides, the edges of grooves or slots would do exactly the same thing, so why are they better?

I've been drilling holes in my own rotors for over 14 years now with great success. Yes, I've only used them on the street, but I wouldn't say I'm a gentle driver and my car is quite heavy. There's a right way to drill holes and a wrong way. Simply saying that drilling holes in a rotor is wrong is a blanket statement and should be considered suspect simply for that reason.

Sure, you reduce the volume of cast iron when you drill holes in the rotor, but the same thing happens when you slot or groove it.

The rotors on my car right now have 32 1/4" holes in them. A very rough calculation shows that I lost 3% of the swept area. I estimate (without the measurements of my rotors handy) those 32 holes count for a little over 1 cubic inch of material lost. That's easily less than 1% of the total volume of the rotor. So, the thermal mass lost by the holes in the rotor is tiny. The benefits of giving the dust and gas somewhere to go very much outweigh the loss of surface area and mass. I'm using Porterfield's R4 compound, so you can't say I'm using an obsolete pad.

There's a right way to do something and a wrong way. Everything is a compromise. A rotor with 100 holes in it does have significant area and volume loss. Don't do that. If you're drilling 100 holes to reduce the weight, you should seriously consider going to a lighter material. There's a point of diminishing returns. I drill at least one hole per vane and just enough to fill the swept area. My current set of rotors have 24 vanes, but to get the swept pattern, I had to overlap a little, so ended up with 32 holes.

If I had a milling machine, I'd try cutting grooves in my rotors. I may just buy some grooved rotors for my Z. Yes, it's a slightly better solution, but not tremendously so for the street. For racing, I agree, use grooves. You should be keeping a close eye on your rotors anyway and replacing them if any cracks appear. I watch mine for the street. Not closely, but I don't ignore them.

Yes, I've seen cracks around holes in the past. My solution was to drill the holes right next to the vanes rather than half-way between them. That reduced the cracking to be just about noexistent.

I'd say my pads and rotors last just as long with holes in the rotors than they would without. I can't back this up because I've had drilled rotors on my Supra since about 2 days after I bought it. I want them on my 5-month-old Z, but haven't had time.

Keep in mind that Stop Tech has a vested interest in making you believe that their product is best. I'm not saying their product is not good, but they'd much rather you buy their rotors than drill your own. Stop Tech's products do look good. I'm sure they are the highest quality and work exceptionally well. But, keep in mind when reading anything they write that they're trying to sell you something. That whitepaper is full of blanket statements and generalizations.

The racers who can don't use cast iron rotors. That's a whole 'nother beast that has its own set of problems and compromises.

No, I don't work for any competitor of Stop Tech. I just wanted to present my experience and my view of Stop Tech's whitepaper.

Asterix

Blue Batmobile

iTrader: (22)

Wow, thanks for the info.

Bat™

aalzuhair

iTrader: (2)

Asterix, Thank you for the write up

J Ritt

iTrader: (4)

Asterix,
Some issues in your write up that I would love to address.

Bite does not arise from the pad rubbing on the rotor. A fresh pad on a fresh rotor has very little bite at all. If I'm lying, go put in some fresh pads, fresh rotors and do a panic stop. Bite comes from the pads interacting with a layer of pad transferred to the face of the rotor, acheived through a proper bed-in of the pads. The edges of the slots do the same thing as the holes, yes that's correct.

Exactly the point of the article, and what we recommend to our customers. As for our vested interest...if you call StopTech and ask what we recommend, we always say slotted for any track driving. Our drilled rotors are actually more expensive than the slottied and plain rotors. Our slotted and plain rotors are the same price. For street and show, we tell people 'whatever you like the looks of'...doesn't much matter.
In addition to the reasons discussed in the white papers, the reason we don't recommend that people drill their own rotors, is because very few people have the knowledge or tools to do so properly!

Agreed...Formula 1 uses carbon rotors...ALMS and prototypes tend to use carbon. They cost $12000+ per corner, and they are paid for by tobacco, tire, and soda sponsorship money. Yes, they are racers that can use carbon. Normal human beings don't use carbon discs...Cart, World Challenge, Grand Am Cup, Grand Am GT, Daytona Prototypes, various touring car series all over the world...pretty much all use cast iron rotors.

kosta157

whens the next formula one event so i can go steal me some carbon discs

pLacebo

Nice post Asterix. But not sure I follow the above statement. The portion of the white paper quoted above simply makes some statements about cross drilled vs slotted rotors but I'm not seeing it as a chance to upsell. JRitt even mentioned that they recommend the less expensive slotted rotors when a car will be tracked or driven hard.
Sounds like you've had good experience in the past drilling your own rotors. Unfortunately most people on this forum (including myself) don't have the experience to drill their own rotors (or simply don't want to). So when choosing between cross drilled or slotted rotors, from any company, it's important to know the advantages and disadvantages of both.

Blue Batmobile

iTrader: (22)

Good info, thanks!

Bat™

Asterix

Good points, and thanks for the reply, J Ritt. I'm glad you responded to my rant.

It's very unusual for a company to recommend something that doesn't make them more money, so I assumed StopTech was no different. I'm glad you proved me wrong.

I thought that my brakes don't work well before bedding in because the pad and rotor don't match perfectly. If they don't match, the friction area is smaller, so the braking force is smaller. When I've looked at my pads before they are really bedded in, I can easily see they're not touching the rotor all over. It's news to me that the pad transfers material to the rotor. How thick is the layer? Could I see it by taking a slice of the rotor and looking at it under a microscope? Obviously, there's some pad-to-metal contact, otherwise the rotor wouldn't wear away like it does. I'm curious.

The two advantages of grooves over holes, as I see it, are that the rotor tends to crack slightly less and they are cheaper. Otherwise, they're the same. I still think all drilled rotors I've seen for sale have too many holes in them.

Asterix

J Ritt

iTrader: (4)

That is true...the pad can't possibly be mated up to the face of the rotor perfectly (more on that in a minute). An additional reason why the brakes won't be very effective if you just throw them in without bedding, is that the first layer of the pad is actually burned off when you do the first bed in cycle. When you do the first bed-in, you usually get fade very quickly...some times as quickly as within 6-7 full blast stops from 60mph. People call this green fade. After you do a first bed in cycle on a new set of pads, take a look around the edge of the pad closest to the rotor. You'll see that the pad material is a different color. That very first layer of pad starts to burn off as you put heat in it. After there's enough heat in the pad and rotor, the pad starts to transfer to the face of the rotor.
You definitely don't need a microscope to see pad transfer. After a good first bed-in, the rotors should be bluish in color all the way around where the pad makes contact with the rotor. That is not just the iron of the rotor changing color, that is pad material stuck on the rotor.
The interface between the pad and rotor is constantly breaking bonds, and the breaking and forming of the bonds depends on the material composition of the disc and pad. When the pad is cold, rotor is cold...you tend to get abrasive friction between the two surfaces...you'll gradually wear off the pad material that you transferred to the rotor. This depends on the compound of the pad obviously. If you do a bed-in with a street compound, and throw on a cold race compound, you will scrape the street pad layer right off rather quickly. I do this on the way to the track normally. I throw in a PFC 97 pad the night before I drive to the event. When you do this, you don't really hear much noise on the first number of stops, because the race pads are still scraping off the street pad layer on the rotor. Shortly thereafter though, your rotors are typically squealing like stuck pigs, because you are rubbing a much more abrasive, metallic compound against an iron rotor. This will wear the rotor down pretty quickly if you drive around cold. Hawk Blue pads are notorious for doing this, because they have such an aggressive composition. That's why we always say, 'if you drive on the Blues cold, you will eat your rotors!'
Where was I...ok, when you get to the track, your rotors are essentially 'clean' again...not much pad deposit on them. They will look more silver than before. Now it's time to bed in the race pads. They need more heat than a street pad to get to the point where they will deposit on the rotor. Therefore, you need higher speed stops to bed them properly (100mph-5mph). If done properly with enough heat, you will get the same effect with a race pad...a nice layer of pad will deposit around the rotor, and you'll be back to blueish rotors.
I guess my point is that you are always wearing off the pad deposit, and the iron of the rotor itself. The type of friction mechanism (abrasive or adherent) is always changing depending on the compound of the pad you are using, and the temperature range that pad is operating in. Also, the metallurgy of the iron rotor itself plays just as much of a role. Some iron is softer than others, and wears down more easily. Generally speaking...with the types of rotors we're discussing, you put down some pad, wear it off...wear down some rotor. Put down more pad, wear it off...wear down some more rotor. It's all about managing this interface. If done properly under a mindful eye, you should be able to swap pads in and out, run in all conditions, and get some good life out of your rotors. You have to know what you're looking at though, and manage these mechanisms. If you don't bed-in your pads, you won't be going pad on pad deposit. You'll be going pad on rotor...you won't get that bite you want, because the pad will be trying to bond with a different type of material (iron). Pad on pad deposit interface is your friend.

I said earlier that I'd get back to the pad and rotor not matching up...you hit on another big topic...the floating rotor. This is precisely the reason why a 2 piece floating rotor is far superior to one piece rotor, or a 2 piece rotor with a fixed hat. When you put a lot of heat in the rotor, it wants to cone. Imagine a rotor lying flat on a table. You heat the rotor, and the rotor wants to expand, right? As the rotor is trying to expand radially, it can't...the center hat section prevents it from doing so...therefore, in our analogy with the table, the edges of the rotor would want to pull up towards the ceiling. With a floating hat, the rotor is allowed to expand outwards without the center hat holding it in place. The mounting holes of the rotor are oval in shape, and allow the drive pins (attachment pins) to move as the rotor expands. Now, turn that rotor vertical and put it on your car. The same thing happens on the track. You heat the system, and the rotor starts to expand...it has nowhere to go, so it actually deforms. You can't look at it and see it moving, but it is deforming. If the rotor pulls or tilts towards the hat, the brake pad can no longer make flush contact with the rotor. Now you are not effectively using the whole surface of the pad face...and chances are, you'll get some tapered pad wear. A lot of people don't realize the importance of a fully floating rotor. If you look at some of the competitions' products, you'll see that the lower price they pass on to consumers is due to cutting costs on little details. We think those details are important.

Whooh...I'm off for Friday night.

ZISBAK

Bat, please let me know if you find any good deal on those type of rotor, I'm planning to change them as well, thanks.

mgl

iTrader: (10)

heres another thread devoted to slotted/crossdrilled rotors.
https://my350z.com/forum/showthread....threadid=69527