Brake Myths: What to Expect When You're Expecting (to Stop)

"Garrett Davis" (GarrettDavis) 02/25/2015 at 14:13 • Filed to: braking, warped rotors, brake fade, technical, drilled rotors, myths

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Brakes are sort of the unsung hero of any good car. Besides showing off those sweet drilled and slotted rotors and rattle-can-red calipers, not many people seem to pay much attention to them until there’s a problem. Good pads and fluid are not exactly among the more “glamorous” upgrades you can do, unlike those 10 degrees of negative camber you have dialed in or that totally functional and not ridiculous wing you have towering over traffic.

I was recently doing a little research into upgrading the brakes on my !!!error: Indecipherable SUB-paragraph formatting!!! which led me down a path to hours of research on the finer details of how our brakes work, and some common ill informed advice we all see day to day. So I figured I’d do my part for the greater good of Jalophood, and pass some of that information along and hopefully clear up some myths and misconceptions about how those things work that allowed your car stop just short of that 3-series that jammed in front of you at the last second at a light that one time and made you like, super pissed.

1.) Rotors: Drilled and Slotted VS Lame and Normal Looking

I wanted to get this one out of the way first, partially because there isn’t actually as much info on these as I expected there to be, but also because it helps to dispel my favorite of these myths.

Quick, picture the hottest new car that you lust after. The one you’d have hanging above your bed if you were still 9 (or maybe now, not judging). Chances are the brakes are huge, flashy, and have more holes drilled in them than Kanye’s ego. So those massive drilled rotors must be the pinnacle of braking technology right now, right?

To help answer that question, let’s first take a look at the brakes of an F1 car:

Image credit

Hmm, besides being incredibly beefy and high tech looking, that rotor and caliper combo doesn’t really look much different in principle than what comes on a modern Camry. It’s a flat disc surface on a side vented rotor. What gives?

Well it turns out that drilled rotors have something of a lasting problem, mostly in that they just don’t. Under high stress and heat, those holes create a whole mess of weak points on the rotor, especially on cheap ones that !!!error: Indecipherable SUB-paragraph formatting!!! , and instead just drill a nice looking pattern whether that means going through the structurally important vane sidewalls or not. Even with good equipment from reputable brands, after repeated heating a cooling cycles, those effin sweet looking rotors start to look like this:

Image credit

So why do drilled rotors exist? Funnily enough, they actually did get their start in racing way back when we still used asbestos brake pads. When these wore down at temperature, pockets of gas created by the pad would reduce brake effectiveness during a race. This was called out-gassing, and our modern semi-metallic or ceramic pads do not have this same problem. So now these holes are put there under the guise of cooling more effectively, which is partially true, because drilled rotors do tend to run cooler. Where there is debate, though, is how much of this effectiveness comes from the ( !!!error: Indecipherable SUB-paragraph formatting!!! ) lack of surface area to create that heat, and how much is due to good airflow. Either way, there are better ways to cool your rotors that don’t involve ruining their structural integrity.

All metals flex and “grow” when heated up, the cast iron rotors on your car are no different. When a piece of metal is repeatedly heated and cooled, it relies on the entire structure to flex evenly along with it. Introducing big, evenly spaced holes just gives the metal more wiggle room to flex on its own as its temperature changes unevenly to the metal around it. Drilling holes means less surface tension to combat this issue. There is no perfect way to heat and cool our rotors completely evenly while driving, so this is just a fact of life. This is why you will never see any serious modern race car running drilled rotors. Go ahead, Google it. I know I did when I first read about this.

So what about slotted rotors? Well a few racing organizations actually do use slotted rotors, Nascar and many LeMans cars included. The idea is that the slots give the dust from between the rotor and the pad a place to go (even though most front pads !!!error: Indecipherable SUB-paragraph formatting!!! ), as well as “wiping” your pads to mitigate glazing (more on that later). The problem here is that if you have glazed your pads, you have already heated them up past their intended heat range, and the pad has literally melted against the rotor’s surface. To say that these slots will resurface your pads for you is both optimistic and ignoring the fact that you pushed your equipment passed what it was designed to handle.

I should mention that one legitimate benefit of drilled and slotted rotors (besides attracting the hunnies, y’all), is in wet weather conditions. The gaps give the water a channel to run out, much like the tread on your tires for better wet weather braking. Also, none of this is to say that blank rotors don’t crack. They do, just not nearly as often and under more extreme conditions.

2.) Aw, Shit! My Rotors Are Totally Warped, Bro!

Nope. They’re not warped and they never were warped. You know what? You’re warped. (Yeah, go ahead and tell mom, I don’t even care!)

I’ll admit, part of the reason why I started doing all this research in the beginning was because I was pretty sure my brakes were warped and I wanted to get new rotors. At first I found all the typical tips and info, but because I’m a loser who researches the absolute shit out of everything, I stumbled upon some people calling bullshit on the whole warped rotor idea. Seriously, I had to look all the way down to like, the bottom 3/4ths of a Google search page to find this stuff. That’s how deep I go for you guys. Anyway, getting to the point...

Here’s a quote from professional racer, Carroll Smith:

“...in more than 40 years of professional racing, including the Shelby/Ford GT 40s – one of the most intense brake development program in history - I have never seen a warped brake disc.”

This is from an extremely interesting write up that he did for StopTech years ago, and if you want to get really in depth with this stuff, I suggest you !!!error: Indecipherable SUB-paragraph formatting!!! along with some of the other !!!error: Indecipherable SUB-paragraph formatting!!! they have published on their site, some going deep into the physics and chemistry of it all — and by deep, I mean half the stuff flew about 7.5 feet right over my head. I’ll give you a more simplified version of what’s going on when your rotors feel and have been measured to be warped. Pay attention, there will be a quiz later.

First, we need to establish how your brakes work.

When applying the brakes on your car, the caliper squeezes two brake pads to the spinning rotor, creating friction against the rotating mass of your tires and slowing you down. There are two types of friction at play here, abrasive friction and adherent fiction. Abrasive friction literally breaks the bonds of the crystalline structure of the pad and even the cast iron of the disc, creating heat. Mohs Law tells us that the harder material (ideally the disc) wears away at the softer material of the pad as the two materials rub together. Picture a sanding pad against a board. Same concept.

Adherent friction is where some of the pad material literally adheres to the opposing surface as they scrape by each other, creating a thin and (ideally) even layer of pad material on the face of the rotor. That material can continually break its bonds and transfer from surface to surface back and forth between the disc and the pad, continually breaking and reforming like they were bouncing across political parties between elections (heyoo!).

Good performing pads need to strike a balance between these two types of friction. A primarily abrasive pad will have a quick wear rate and will fade at high temperatures as its structure weakens and gives, no longer stiff enough to be abrasive. A primarily adherent pad will result in too much build up, as it is not abrasive enough to scrape the disc clean and uniform, and requires much higher temperatures to be effective. Between these two is where the balance needs to strike for good street pads — something that can handle being ridden all the way down a long hill without fading to nothing once you reach the bottom, and something that can still stop your car effectively on a cold morning. This is why a racing pad that requires high heat to work effectively and can be so dangerous on the street.

So how do my brakes “warp” then?

So going back to that adhesive friction stuff, if a pad is not properly broken in (yes, this is a thing), the material that transfers between the pad and the disc can do so in a seemingly random, uneven fashion creating islands of deposits that keep growing, leaving high and low spots on the disc. Another problem is if you hold the pad against the rotor after intense braking or coming down from a high speed, the pad can literally leave a print of material on the disc like the image from !!!error: Indecipherable SUB-paragraph formatting!!! above shows.

The other way your rotors can feel warped happens when your discs develop heat spots. Modern cast iron rotors are an alloy of iron and silicon mixed with particles of carbon. At high temperatures, spots of silicon carbides form and create uneven hot spots, growing in temperature faster than the iron around it. Once this temperature reaches up around 1300 degrees Fahrenheit, the cast iron around that area begins to form cementite, or !!!error: Indecipherable SUB-paragraph formatting!!! which is very dense, abrasive, susceptible to cracks, and conducts much more heat than the cast iron around it. Once the cementite forms, continued use will just heat up those spots, causing them to heat the iron around them and form even more cementite. It’s a vicious cycle.

Resurfacing your rotors can remove the cementite if you catch it early enough, but it’s very unlikely and most times you’ll be back in the shop after a few months getting them replaced all together. It’s a band aid fix for a larger issue, and honestly isn’t even really all that cost effective over a set of decent replacement rotors and the knowledge of how to keep this from happening again.

!!! UNKNOWN HEADER TYPE (MULTI-LINE BREAK?) !!!

Image credit

We all know what brake fade is, and have likely experienced it in one form or another, but what isn’t always clear is what exactly is happening to make our brakes less effective after hard use. I’ve covered a bit of this already, but I’m going to go into more detail. Why? Because I feel like it, god damn it! And I want this article to be so long that it alienates 62% of readers and only leaves the Jalop-elite still with me. So if you’re still reading this, congrats, you’re even less productive at work than most of your peers. Oh, and don’t forget to flush once you’re done — Stan from accounting complained the other day. I know, I hate Stan too. I digress...

There are three reasons why your brakes fade, and they are not necessarily mutually exclusive. I already covered why the more “average consumer” friendly pads lose their abrasiveness after being overheated, but I’d like to talk about pad glazing and the effects of overheating your brake fluid. More specifically, why some brake fade leaves your pedal feeling healthy and firm, but with decreased effectiveness — and why other times your pedal will feel squishy and soft, forcing you to pump the pedal to get any performance out of the system. (Feel free to add your own innuendos to the previous few sentences, I’ll wait.)

Glazed Pads

Pad glazing is when the surface of the brake pad literally melts and hardens, leaving a dense, smooth material that slides easily across the rotor. This will result in a normal pedal feel, but requiring much more effort to achieve adequate braking. A glazed pad has lost its porous, almost flaky surface and instead is left with an almost glassy, hard face for it to slide on. Properly bedding in your pads to the manufacturer’s spec can prevent this. Most performance oriented aftermarket pads will come with a guide, but a broad one can be found !!!error: Indecipherable SUB-paragraph formatting!!!

Last but certainly not least, we find ourselves on possibly the most neglected and ignored item on any car, possibly only losing out to the blinkers on your average BMW (now an optional extra!):

Brake Fluid

The brake fluid sitting in your car is actually one of the most important fluids in there to keep track of. A lot of people, myself included for the majority of my years, never really consider brake fluid as a consumable item. It’s not until you learn a bit more about hydraulic fluid and racing brakes that you realize that brake fluid is something you should be watching more closely.

Probably the most common form of brake fading you’ll come across shows itself through a squishy brake pedal. This happens when the brake fluid in your calipers literally boils from the extreme heat being generated under hard braking. The reason this is a problem is that brake fluid is chosen specifically for its incompressibility and once the fluid boils, it generates air bubbles. As we well know from the glory of forced induction, air compresses a lot and quite readily. Once those air bubbles form, each push of the pedal puts more energy into compressing the air and less into squeezing the rotor, sometimes to the point where even putting the pedal all the way to the floor won’t stop you adequately.

Once your brake fluid has been cooked, pumping your brakes can return some pedal feel, but bleeding your brakes is the only way to now remove that air from the system. Still, once your fluid has boiled, you should change it out for some fresh stuff at your earliest convenience, because boiled hydraulic fluid has lost much of its heat resistance and will boil much easier the next time.

Another thing to keep in mind is that brake fluid is extremely hygroscopic, meaning it will readily absorb moisture if left exposed. This is a problem because adding water to the mix substantially decreases the temperature at which the fluid will boil. As little as a 3% water content can bring the boiling temperature of the fluid down by as much as 150 degrees Fahrenheit — or about 30%. Water will find its way into your brake system over time, especially if you live in a humid area, which is why even under normal daily driving conditions, you should still change out your brake fluid semi-regularly.

Whew. OK. *catches breath* That wasn’t so bad.

There are of course tons of things I left out, enough that I might have to dedicate a whole separate article to them, but this takes care of the more basic and important stuff. A few caveats to include here: One, I really don’t know how much of all this applies to something like carbon-ceramic brakes like on the GT up there. This is still fairly new territory, and pretty much all the info I gave up there applies to the much more common cast iron discs. Second, all this talk of brakes and their effectiveness leaves out the importance of tires and suspension. Your brakes can only do their job as well as the tires are able to stick to the surface, something that proper suspension geometry and damping can greatly aid.

Note: I’m thinking about making a whole series of these features, focusing on the different major systems of modern cars each time; things like suspension, cooling, tires, and ECUs/tuning — all depending on the response I get. If you hated this, feel free to let me know so I can write more, or if you enjoyed this I’ll quit while I’m ahead. Something like that, anyway. So let me know what you guys think!

Hat tip to !!!error: Indecipherable SUB-paragraph formatting!!! and !!!error: Indecipherable SUB-paragraph formatting!!! , more great info to be found there.

Party-vi > Garrett Davis 02/25/2015 at 14:19

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Just fantastic work here. Finally someone else realizes hole and slots (giggity) are there for looks and not really function anymore.

Bozi Tatarevic > Garrett Davis 02/25/2015 at 14:23

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Great article and mention of the Carroll Williams comment

Garrett Davis > Party-vi 02/25/2015 at 14:24

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Thank you! If I can prevent just one cracked disc on someone's brown autocross Miata, I will have done my job.

RallyWrench > Garrett Davis 02/25/2015 at 14:28

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Excellent post, I hope it gets FP'd. This should be *ahem* drilled into everyone's minds often. The warped brake myth in particular is always a fun one to explain to customers. One correction: It's Carroll Smith, not Carroll Williams, and yes, his work is gold. I keep a copy of Engineer To Win in my race toolbox.

Garrett Davis > RallyWrench 02/25/2015 at 14:31

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Whoops, good catch. When I read your post I was like "huh, Carroll Williams? What's he talking about?"

Brain fart when actually typing out the name, I guess. Yeah, I have a few of his books, all great stuff.

SidewaysOnDirt still misses Bowie > Garrett Davis 02/25/2015 at 14:35

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Great, great article! Something that might be worth noting under brake fluids is that generally, quality high temperature brake fluids are more hygroscopic than what Honda put in in 1992 and will need to be changed more often.

Officer Jim Lahey is not a real cop > Garrett Davis 02/25/2015 at 14:35

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Thanks, very informative!

BigBlock440 > Garrett Davis 02/25/2015 at 14:38

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The warped thing gets me, I'm not sure I buy it yet. It kind of makes sense, but I have seen enough metal warp after uneven heating/cooling that I always believed it. I've also heard that over-tightening or unevenly tightening lug nuts could cause the rotor to warp, so I don't know. I don't know how you'd be able to tell either way though without cutting the rotor in half and putting a straight edge on the part that doesn't touch the pads.

Garrett Davis > SidewaysOnDirt still misses Bowie 02/25/2015 at 14:38

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I thought about that, as well as going into the differences between DOT 3, 4, 5, and 5.1, and glycol VS silicon based fluids, but it was just getting too long. I'm thinking of doing a "prepping for the canyons" type article that would go into more detail on a lot of this stuff.

Thank you!

Garrett Davis > Officer Jim Lahey is not a real cop 02/25/2015 at 14:39

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Thank you, officer. I'll keep it under the limit.

E. Julius > Garrett Davis 02/25/2015 at 14:44

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Sweet read. When can I expect my Jalop Elite card to arrive at my house?

Jake Huitt - Two Alfas And A Nissan, Not A Single Running Car > Garrett Davis 02/25/2015 at 14:46

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Please make more of these. Good read and good info.

Garrett Davis > BigBlock440 02/25/2015 at 14:50

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The over tightening or uneven lug nuts cause heat spots due to more pressure on the pad in those areas versus others due to increased run out, creating those heat spots like I mentioned above, either in raised pad material deposits, cementite matrices or both.

One form of "warping" that I didn't mention because it is rare, and only really happens in racing environments, is the rotor material between the cooling veins collapsing inwards from heat and pad pressure. Once both are heated up way passed any safe point, the pad and rotor will form sort of waves as they squeeze over the cooling supports in the rotor.

There is also brake distortion in the form of uneven wear from center to the rim with uneven thermal expansion, but this is a whole other story.

I do highly suggest checking out StopTech's technical section on this stuff. There is a ton of info on this and how it happens, and they go much more in depth than I have here.

http://stoptech.com/technical-supp…

Garrett Davis > Jake Huitt - Two Alfas And A Nissan, Not A Single Running Car 02/25/2015 at 14:55

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Thank you!

Garrett Davis > E. Julius 02/25/2015 at 14:55

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Aw, shit. Now I need to print some...

Thanks!

uofime > Garrett Davis 02/25/2015 at 15:00

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Good post, you should add some tags your post so people can find it later.

Jordaneer, The Mountaineer Man > Garrett Davis 02/25/2015 at 15:01

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maybe you'll end up braking kinja (see what I did there :) by this getting so many views, really great article Garrett!!!

Garrett Davis > uofime 02/25/2015 at 15:03

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Good idea, thanks!

Garrett Davis > Jordaneer, The Mountaineer Man 02/25/2015 at 15:04

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Thank you!

Takuro Spirit > Garrett Davis 02/25/2015 at 15:13

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Fun Fact About Takuro:

I once got a call from a library I hadn't visited in YEARS and was told I owed them for a copy of What To Expect When You're Expecting that hadn't been returned.

Once I explained I was A DUDE, and 13 years old when the book was taken out (I was now 20ish) the lady laughed and said due to that fact, and statute of limitations, I would be let off the hook.

FP EDIT: Oh great, now everyone's gonna know. :/

You can tell a Finn but you can't tell him much > Garrett Davis 02/25/2015 at 15:14

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...only leaves the Jalop-elite still with me.

Woot, woot! I'm elite!!!!

So if you're still reading this, congrats, you're even less productive at work than most of your peers.

Ohhhh.

Hey look, shiny brakes.

Garrett Davis > You can tell a Finn but you can't tell him much 02/25/2015 at 15:16

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Mmmm, those Polo WRC cars make me feel things. Dirty things.

BigDub > Party-vi 02/25/2015 at 15:16

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Not to mention they wear out pads quicker, are more noisy, and can induce excessive vibrations...

detailer4u > Party-vi 02/25/2015 at 15:16

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Exactly my thougths. I know there is a weight / balance advantage to the treatment on these, but other than that ...... mind you that is what the design / engineers told me.

They do look fantastic though.

jcpwn3r > Garrett Davis 02/25/2015 at 15:16

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I was told at some point by someone (who could have been completely full of shit) that drilled rotors have the benefit of providing from extra stopping force from the hole edge biting into the pad when you stop. Not a MechE so can anyone confirm

RexSeven > Garrett Davis 02/25/2015 at 15:18

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I bought a 1993 RX7 in 1998. It had 12,000 miles on it. At 36,000 miles, my 3rd set of rotors and pads were toast. I drove aggressively, but not insane. I decided to get some drilled and slotted rotors from Brembo and EBC Red Stuff pads. At 125,000 miles I put on my next set of rotors and pads. I don't know if it was the holes or slots or just the quality of the rotor itself, but I get drilled and slotted rotors from reputable companies every time now.

Megamullin > Garrett Davis 02/25/2015 at 15:20

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For the love of everything that is decent and good in this world, please devote some time to making a whole series of features focusing on the major systems of modern cars. Please!

71MGBGT Likes Subarus of Unusual Colors > Garrett Davis 02/25/2015 at 15:20

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Any idea about the relationship between drilled rotors and rotational inertia? Will removing weight is the form of holes reduce unsprung weight thuss making the car faster?

PhilKesselRun > Garrett Davis 02/25/2015 at 15:20

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Okay, can you help me with this. When I press on my brakes I get this pulsing sensation. Discs up front, drums in back. It always gets worse, or more noticeable, after moderate-heavy braking. Wheel shake is not uncommon. What's causing this and is there something I'm doing to make it more likely to happen after I get my brakes fixed?

Garrett Davis > RexSeven 02/25/2015 at 15:21

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None of this is to say that drilled rotors can't perform, just that they have a tendency to crack much more easily, and also have marginally increased pad wear. If you were to have bought some good blank rotors (or just slotted) of the same quality and with the same pads, I'm sure you experience would have been the same.

Garrett Davis > jcpwn3r 02/25/2015 at 15:23

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That does lead to increased pad wear, especially in ones that don't dimple the edge of the hole, but it does nothing to help stopping force. The only thing that will help that is increased surface area in proportion to the caliper piston diameter. Those need to strike a balance for the best stopping power.

PJ > jcpwn3r 02/25/2015 at 15:23

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I would think given the flat surface nature of the face of the rotor and the pad material that this wouldn't happen. Also, a bunch of holes biting out chunks of pad material unevenly would be less than optimal.

AMC/Renauledge > Garrett Davis 02/25/2015 at 15:24

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VERY helpful and interesting stuff here. Thanks a million for doing this!

Doctor-G-and-the-wagen > Garrett Davis 02/25/2015 at 15:24

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Woah woah woah, stop. Just stop right there.

Did you stop?

Then you have good brake knowledge!

472CID > Garrett Davis 02/25/2015 at 15:25

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So you're say that wabbly brake performance comes from an uneven layer(s) of brake pad residue and not the rotor physically bending out of shape? cause that would make more sense not that I think about it.

StndIbnz, Drives a MSRT8 > Garrett Davis 02/25/2015 at 15:26

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Very well written. Good job sir.

doodon2whls > Garrett Davis 02/25/2015 at 15:28

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Bravo.

SLOWCLAP.GIF

I wish I had the time and patience to put this kind of knowledge down on paper or in a post like you just did...

You could write several tech-bits on brakes alone, and then work your way through the other vehicle sub-systems. Up/Over-sized brakes, Pad compound selection, Brake M/C changes, etc.

Then Steering... Geometry, EPS/EHPS/HPS/Manual system tradeoffs, etc.

Word of warning - stay away from tires and oil... Those topics have been beaten to death on enthusiast forums over the years. Someone (like you or I) goes in with facts and data, and then the whole fukken enthusiast army comes down on them because he said XYZ snake oil or PDQ cheap tires are BS.

klurejr > Garrett Davis 02/25/2015 at 15:28

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do more, I liked this and learned a bit. Also, can motorcycle rotors warp? My last bike had terrible vibrations under front braking and everyone told me they were warped and needed to be replaced. Motocycle rotors are much smaller and thinner than automotive rotors, and my bike came with drilled rotors from the factory.

Garrett Davis > PhilKesselRun 02/25/2015 at 15:28

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More than likely you have high spots of built of pad material, or formations of cementite. Either one will put vibrations through the pedal and even the steering wheel under braking. Depending on how long this has been going on, you may be able to get them resurfaced, but I'd advice against it. Just get new quality pads and rotors and read up on how to prevent this from happening in the future.

Although, it could be completely unrelated to your rotors, and could be something like ball joints or bearings that are wearing out. Either one can cause those symptoms. One quick way to tell is to jack up your front end and see if there is any lateral or vertical play in the wheel. If so, take it to a mechanic.

jnecr > Garrett Davis 02/25/2015 at 15:29

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Nope. They're not warped and they never were warped. You know what? You're warped. (Yeah, go ahead and tell mom, I don't even care!)

Exactly, I've been saying this shit for years and nobody believes me. When people say they're going to "get their rotors turned" because their rotors are warped I tell them to ask the mechanic what that means. None of them ever do, but they still happily pay $100 for the "work."

HammerheadFistpunch > Garrett Davis 02/25/2015 at 15:29

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Clap clap clap

volvo_4_life > Garrett Davis 02/25/2015 at 15:31

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Great article! Will stay tuned for more!

sillywabbit > Garrett Davis 02/25/2015 at 15:31

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Awesome article. I learned a thing! Time for some new brake fluid as well.

Buckner > Garrett Davis 02/25/2015 at 15:31

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Perfect timing! I just ordered a drum to disc conversion for the oldz. (ok, yesterday) I only had 500 to throw at the oldz this winter and decided that braking was indeed a thing that I needed. Brake fade in a 4700 lb drummed monster is exactly what you expect. I was looking into slotted brakes just for the looks, cuz what performance does a 4dr HT really represent even with a v8. However- now I will save the fancy rotor money and buy more lawn darts and cheap beer. Thanks!

Tom > PhilKesselRun 02/25/2015 at 15:32

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Brakes are not the only thing that can cause that, but I'd recommend starting with new rotors on the front (and pads of worn), and taking it easy on them for the first 500 miles or so. If you still experience the issue, look into wheel balance and wheel bearings - albeit both less likely but possible causes to what you describe. This is based on my own person experiences over the years, so someone more knowledgeable may feel free to come in to contribute and / or correct me.

Garrett Davis > 71MGBGT Likes Subarus of Unusual Colors 02/25/2015 at 15:32

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I would say it is very, very minimal. One thing I didn't cover in the article is big brake kits versus upgrading stock size. If you look at a lot of Rally cars or even LeMans racers, a lot of times their rotors aren't actually all that huge. The most important ratio for good braking is the surface area of the disc versus the caliper piston diameter. A disc too big for the pistons will not perform as well as a smaller one, and pistons too big and powerful for the disc size will just destroy your rotors.

I'll go into this stuff more in a future article.

Garrett Davis > Megamullin 02/25/2015 at 15:32

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Thank you! I definitely will, the response has been great so far and I have plenty of ideas in the hopper.

ESSSIX GmbH - Accountant/Wagon Thumper > Garrett Davis 02/25/2015 at 15:33

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I had Stoptechs... pad prints were the worst. Most labor intensive set up ever.. even with street pads, it wasnt possible to keep this from happening. and It also didn't take much to leave a print either. So I was rebedding the rotors at least once a month.

But they did look awesome, and stopped like hell. Filled the wheels up nicely too!

Herr Quattro - Has a 4-Motion > Garrett Davis 02/25/2015 at 15:33

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I like this series.

Is there anyway you'd cover stroke vs Bore and their performance value?

T off the New > Garrett Davis 02/25/2015 at 15:33

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I was hoping to see a pic like this as soon as I read the title, thank you

PhilKesselRun > Garrett Davis 02/25/2015 at 15:33

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Thanks for the response. I'm pretty sure it's just build up on the pads since when I took it into Just Brakes Your Bank TM to get it looked at, they didn't try and screw me out of money to replace that.

Also, how often should you change your brake fluid? I live in humid as hell Texas FWIW.

rksjalop > Garrett Davis 02/25/2015 at 15:34

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Great article, truly informative! Yes please to more like this on any/all systems.

Michael Maguire > Garrett Davis 02/25/2015 at 15:35

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Wow, I actually thought you were a Jalopnik writer until I saw a comment about hoping it gets FP'd. Very good work and I would gladly read about the other myths among modern car systems.

Keep up the good work!

Loki240SX > Garrett Davis 02/25/2015 at 15:35

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Can confirm, my cheap (but cool-looking!) 240SX Z32-swap rotors look just like this.

Garrett Davis > rksjalop 02/25/2015 at 15:35

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Thank you!

windadvisory > Garrett Davis 02/25/2015 at 15:36

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Fun Fact - Many motorcycles come from the manufacturer with drilled rotors. (Even my mountain bike's Avid hydraulic disc brakes have them) Why? Partly for water dispersion, partly to enhance cooling on very thin, light discs. But mainly for lower weight to reduce gyroscopic precession, particularly on the front.

BigBlock440 > klurejr 02/25/2015 at 15:36

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Probably. Motorcycle rotors are a single, thin, piece of metal, not two thick pieces connected together. But I could be wrong.

MC20 > Garrett Davis 02/25/2015 at 15:36

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Something I noticed @ the Detroit show this year, almost every car had these floating rotors. pretty cool if you ask me

Garrett Davis > PhilKesselRun 02/25/2015 at 15:36

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It's tricky to tell. Depending on how you drive your car, anywhere from every few months to every year or so.

KazVH > Garrett Davis 02/25/2015 at 15:37

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Why are motorcycle rotors cross drilled?

Captain_Spadaro > Garrett Davis 02/25/2015 at 15:37

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BMW is the only manufacturer that actually specifies a service interval for brake fluid. No one else does, to my knowledge.

Drakkon- Most Glorious and Upright Person of Genius > Garrett Davis 02/25/2015 at 15:37

5

So a 'warped' rotor is still smooth (in one plane) but has areas of grabbiness and not-so-grabbiness? Is that what you are saying?

While I may buy into that, I have down run-out tests on them before and found less than flat rotors so while I'm not calling BS on your calling BS, I still question it.

The other is the douchbags at the tire store that left the lug-gun on the 'breaking' setting for taking lug nuts off, but instead use it for putting the lug nuts back on. Now those rotors I promise you are no longer flat and make a car almost undrivable. Good luck getting the store manager to play ball on a new set. Your brakes were clearly worn when you came in, you should buy another set.

Garrett Davis > Herr Quattro - Has a 4-Motion 02/25/2015 at 15:37

4

I was thinking about that, actually, not a lot of people really know the difference between bore and stroke, as well as the importance of valve timing and what an aggressive cam really does. This will all get its own article.

Thank you!

liquid_popcorn > Garrett Davis 02/25/2015 at 15:38

1

Very cool article, and definitely helpful information for me as I am about to tackle new brakes for the project! Thanks for posting.

Party-vi > jcpwn3r 02/25/2015 at 15:38

35

Yep. Sounds like they were completely full of shit.

BMWhat > Garrett Davis 02/25/2015 at 15:38

2

Now I'm not into gimmicky shit, and I love the research done here, so I will share my tail of slotted rotors actually being functional. I had a Cobalt SS/TC that from the factory had Brembos with smooth rotors on the front. Shortly after getting the car, I was driving in a decent rain storm. After driving for a few miles on the highway, I went to apply the brakes and absolutely nothing happened for about 2-3 seconds, until the rotor dried off and then it grabbed. It consistently did this until I switched to a slotted rotor and voila, that solved the problem.

Vintage1982Benz > Garrett Davis 02/25/2015 at 15:39

4

So if you're still reading this, congrats, you're even less productive at work than most of your peers.

Thanks a lot, Oppo and Jalopnik!

Burt > Garrett Davis 02/25/2015 at 15:39

3

Excellent article! One thing I've seen, that I believe you at least partially in a comment below, is rotor size. A lot of people assume that the larger rotor diameter, the better, and while generally, the more thermal mass and swept area, the better, one thing a lot of people don't take into account is rotor thickness. Raybestos makes a 6 piston brake kit designed to fit in a 16" wheel, and I believe it's pretty much the same setup that NASCAR uses for road courses. The rotor has a relatively small diameter, but the pads and rotors are massively think. Thermal mass is thermal mass, no matter which way you slice it.

Also, with carbon ceramic brakes, from the little I've looked at them, the rotors AND pads are able to withstand significantly higher temperatures than steel rotors, as in several hundred degrees F higher. The fluid has to be upgraded accordingly, as well, but thermal capacity is the big difference.

MC20 > Garrett Davis 02/25/2015 at 15:39

1

The drilled and slotted rotors you buy on Amazon most likely are the cheapest chinese rotors they could source and then machine on. If youre going to buy something like that for the "cool effect, get a Willwood, Hawk, etc. Even those Ive seen look like the rotor in the picture but those were on race cars.

Garrett Davis > ESSSIX GmbH - Accountant/Wagon Thumper 02/25/2015 at 15:39

0

Good performance pads and rotors are actually a lot of work to keep functioning correctly, especially under spirited driving. Even performance leaning street pads take special care to last.

Also, dayum. Love the Audi, man.

Burt > Burt 02/25/2015 at 15:40

0

For whatever reason, when I'm on here and working simultaneously I seem to stroke out and leave out words altogether, so sorry about that.

Zaxxon > Garrett Davis 02/25/2015 at 15:40

1

While I realize that the slotting/drilling does not do much, it's hard not to like the look.

User1312 > Garrett Davis 02/25/2015 at 15:40

1

Great write up!

Garrett Davis > Buckner 02/25/2015 at 15:41

2

Good quality blank rotors from Brembo or StopTech actually aren't all that expensive, and well worth saving the money over drilled.

Anything that adds more beer to the equation is usually the correct answer. Fact.

BMWhat > Garrett Davis 02/25/2015 at 15:41

8

Another key item to note is that with some of the racing fluids, they come in two different colors so you run "gold" one time, then "blue" the next time. This ensures that you get all of the old fluid out when you are changing fluids.

jacknifetoaswan > Garrett Davis 02/25/2015 at 15:42

3

The important part is the swept area, yes, but bigger discs allow for better heat dissipation, as well as the ability to utilize larger pads. A big brake kit from a reputable manufacturer (Baer, Wilwood, Brembo) will be engineered for each specific vehicle, and will include upgraded rotors, pads, and calipers that are designed to increase rotor size, pad swept area, heat dissipation, and resistance to fade.

Garrett Davis > jnecr 02/25/2015 at 15:42

0

Every time. What's worse is that new high quality rotors aren't actually that expensive, and they'll be doing it in the end anyway.

5mtFXT > Garrett Davis 02/25/2015 at 15:43

1

Great article. Brake pads/rotors/fluid are always one thing people tend to forget about when they're doing mods. If you are going to get going faster you need to be able to stop faster, too. Keep up the great articles.

Spool Junkie > Garrett Davis 02/25/2015 at 15:43

1

Fantastic write good sir. Looking forward to more in the future!

alan > Garrett Davis 02/25/2015 at 15:43

1

bought drilled rotors year ago thought it would look nice. and had this cracking problem. also they made clicking sounds when braking like sticking a pencil in a fan. other than looks, never bought a set again

Remember dialing "popcorn" for the time? > Garrett Davis 02/25/2015 at 15:43

1

Great article, and definitely, keep on writing! I had come across that Stop Tech article on pad buildup before, but you covered other areas that I hadn't seen.

Excellent work!

KC-10Paul > Garrett Davis 02/25/2015 at 15:43

5

Good write up, you should do one next on why this is incredibly stupid.

Computerbudda > Garrett Davis 02/25/2015 at 15:44

1

Keep up the good work. Also touch on fake ho-ha adornments available for our project cars.

mcseanerson > Garrett Davis 02/25/2015 at 15:44

7

So my brakes are pulsing on my '96 Regal. If I understand your article properly I should replace my rotors with just basic rotors, replace my brake fluid, and replace my pads with good but not racing level brake pads. Is that right?

Congrats on the FP, definitely a thorough and worthy article.

Herr Quattro - Has a 4-Motion > Garrett Davis 02/25/2015 at 15:44

2

yes !

jacknifetoaswan > Garrett Davis 02/25/2015 at 15:45

1

This is a great article! Thanks for typing this up!

If you do a future 'part 2,' you might want to talk about the differences between types of brake hoses, and what steel braided lines do, as well as maybe make a recommendation, based on your research, on whether they're worth the cost.

Loki240SX > Garrett Davis 02/25/2015 at 15:45

1

What about heavy braking and then immediately traveling through deep water? I'd think quenching would do some damage to the rotors.

E39Geek > Garrett Davis 02/25/2015 at 15:45

2

Yes, keep 'em coming. I had to learn a lot of this after my car — which I drive roughly 3,000 miles/year — developed "warped" rotors according to the dealer. In reality, the car was driven a couple of times in crappy (cold and wet) weather and then stored outdoors for several months while I was recovering from surgery that kept me from using that 3rd pedal we all know and love.

Over time sitting in the driveway outside, the pads just leached material onto the rear rotors and a hard stop would shake the fillings out of your teeth. I got a cheap runout gauge and found high spots matched perfectly to pad-sized marks on both of the rear rotors.

The dealer wanted over $2,600 to replace all four rotors and their pads even though another dealer (same network) had just replaced the fronts less than 2,000 miles earlier. They did not get my business. I did the rear brakes myself for around 1/4 of that and learned a heck of a lot doing the work. I saved a ton of money and learned a useful skill.

ArthurJenson > klurejr 02/25/2015 at 15:46

1

all the same principles apply to bike rotors with a few minor differences. The rotors are so thin, and in most cases use a floating mount, that lateral runout or "warping" is actually pretty comon and usually not a problem or source of vibration. There will be a spec for allowable runout in the factory service manual for your bike along with a procedure to test it. Most commonly pulsing brakes on a bike are due to overheating or pad contamination, pull the pads and deglaze them by sanding lightly against a piece of fine grit paper layed on a perfectly flat surphace, a piece of window glass works nicely. While you are at it a light hand sanding of the brake disc is a good idea. Clean everything thouroughly with brake cleaner and reinstall. If that solves your vibration then you had a pad issue. If not it's likely that the disc itself, which will likely have to be replaced because it's very very hard to machine rotors so thin. Oh yeah, wavy rotors and fancy hole patterns, don't really do anything for cooling, but they are pretty cool looking, factory OE or a basic replacment from galfer, EBC, braking etc would be a solid choice

Oh yeah, change your fluid too, it's due I promise

ldympr > Garrett Davis 02/25/2015 at 15:46

1

Like the article, very informative. Love it when I can learn new things and/or reinforce things I already know. 500 stars.

Curious-there is a three piston brake, I know it was used in FF6 Daytona. what are thoughts?