There is more misinformation about cross drilled rotors than anything else I can think of on a car. The general consensus seems to be that drilled and slotted rotors offer better performance than “blank” rotors. This is simply not the case.
At one point in time race cars did have cross drilled rotors, and this is probably where the idea that they offer increased performance came from. But if you look at any serious professional race car today, I would be shocked if you found any cross-drilling.
Like everything else, there are advantages and disadvantages to drilling and slotting a rotor. Fortunately, technology has progressed so that there is no longer a need to cross dill rotors and therefore, we don’t have to deal with its disadvantages.
The reason why rotors were drilled in the first place was to relieve the gas that was created when the pad material started to breakdown (burn). Since modern pads don’t gas off any significant amount, this is simply not a concern.
Many people and advertisements claim that cross drilling helps the rotor cool. I’m sure those little holes do help the rotor cool in some regard (possibly not measurable), but the effect in reality is completely insignificant. Furthermore, any benefit of extra cooling is most likely off set by the reduction of the rotors mass due to the drilling which lowers the overall heat capacity of the rotor.
So now that you know that there is no benefit to running a cross drilled rotor, we are left with a major disadvantage. What all of those little holes do is create stress risers and a surface that’s unevenly heated and cooled. The result is that the rotor becomes very easy to crack and makes a catastrophic failure much more likely. The worst situation is when a crack forms and connects between multiple holes – much like a connect-the-dot puzzle. This can lead to a large piece of the rotor breaking free which I can assure you is not good at all.
So why do all those high dollar cars like Ferrari, Lamborghini and Porsche have drilled rotors? Well, because people think it looks cool. The rotors on those cars fail when pushed hard as well, and the professional race teams that run these cars replace them with non-drilled rotors. In my experience, cross-drilled rotors just don’t last as long as a blank rotor. If you ever go to the track and find someone pushing a car hard that has cross-drilled rotors, put your ear near one of his wheels and listen carefully when he gets back to the paddock. You will hear small metallic pings and pops as the rotor cools unevenly. What you will be hearing is the sound of the cracks forming….
So what about slotting?
Slotting serves the same purpose as drilling but doesn’t weaken the rotor as much. Slotting is also advertised to “wipe” the surface of the pad preventing glazing. I don’t know how much of this is true or how much of an effect this has, but the real world result of this is that your pads don’t last as long. Typically, if you glaze your pads, you have already surpassed the heat range of the material and the pad will most likely have “melted” onto the rotor surface creating an uneven transfer layer. I don’t see how slotting is going to prevent this.
So what really happens when the rotor is “warped”?
When you’re on the brakes and there’s a pulsing sensation or vibration, we typical call this situation warped rotors. Surprisingly, I have placed a dial indicator on so-called warped rotors to find that they have no run-out what-so-ever.
What does happen is that the layer of pad material on the rotor surface builds up unevenly, and also, the metallurgy of the rotor can change states. The layer of pad material on the rotors surface, if unevenly distributed, will create hot spots. If these spots get hot enough, it can form cementite in the rotors metal – a rough iron carbide formation that creates a lot of friction, but is terrible at dissipating heat. The cementite formation can get so bad and cause so much friction that even when you are off the brake pedal completely, because your pads are always in contact with the rotor ever so slightly, it can create a vibration when driving normally. I have even mistaken this vibration as my tires being out of balance.
Uneven transfer layer buildup and cementite is what produces “warped” rotors, not run-out or distortion*. Cementite is a problem with iron rotors, rotors made of other materials like carbon do not suffer from this problem.
Vibrating can also be caused by a crack in the rotors surface. If you have a vibration that only appears during hard or extended braking, it may be a crack. The reason for this is that the cracks opens up when the rotor is hot and closes when it’s cold. You may never even know that there is a crack if you never build heat in the system…
*Let me digress a little bit – There is surely some uneven dimensional change (warping) to the rotor if you have a localized hot spot. But this seems to be only temporary and when the rotor cools, it returns to its normal flat state. I suppose you could drive through a puddle with very hot brakes and cause a permanent measurable change, but it must be rare. Also, yes, it is possible to have an actual warped rotor or one that was not cut square. In those cases, yes, they will cause a vibration.
If I have my rotors resurfaced, will that fix the problem?
In my experiences, no. When I have had my rotors resurfaced, it only cured the vibrations temporarily. Within a few months, they return even if I haven’t been doing any hard driving. So what gives? Most likely, parts of my rotors had turned to cementite and it was thick enough where resurfacing did not remove it all. Even if there was a small area left after resurfacing, that one spot will create a hot spot which will grow in fairly short order. This is also proof that the vibrations are not coming from a warped rotor.
Food for thought:
- So actually there is one benefit to cross-drilling and slotting but I didn’t want to mention it since it’s also insignificant – that benefit is in wet weather. It turns out that drilling and slotting either give a place for water to evacuate like the tread on a tire, or allows steam to gas through kind of like what drilling was intended for. I don’t know what really happens, maybe both. But either way, the initial bite tends to be better in the wet.
- Many people have such strong convictions about rotor warping that they wont believe anything I say in this post. I dare those people to put an indicator on a ‘warped’ rotor and actually find the distortion in the rotors surface. Rotors do tend to have run-out even when new, but you would never know it as long as the run-out is in tolerance; so, don’t mistake some run-out for warping when the rotor had it from the day it was installed and when the pulsations in the brake pedal only started recently. Also, don’t let some fool mechanic cut your brand-new rotors to ‘straighten them out’ or to get rid of the in-tolerance run-out, this will just shorten the rotors life.
- In general, resurfacing rotors is only a band-aid.
- There is different levels of cross-drilling. Some rotors have many more holes per inch than others. The ones with a high density of holes suffer more than ones like the rotor at the top of the page. The results are the same when pushed hard.
- On the street, drilled rotors are ok, but can create noise. The thing that kills drilled rotors is fast heating and cooling cycles over a wide temperature range. This is why no one uses them on race cars.
- The transfer layer on the rotors surface is typically invisible in all but extreme cases. When the pad is overheated, it can leave large visible deposits on the rotors surface.
- Rotors with curved vanes are significantly more efficient than those with straight vanes.
i have cross drilled and slotted rotars. To there credit I have some things to say; Although logically the physics side about what you said concerning heat dissapation and so forth makes sense i have some food for thought. My front right calliper locked. I drove for 3 days on the high way upto 85 MPH or more with out knowing my brake was locked. On the 3rd day my car started vibrating. After all the excruciating heat abuse that the rotar was put through for 3 days my mechanic put the rotar though a test and it was completly unharmed. I only needed new pads and callipers. My (extremley suprized and knowledgable mechanic said) if it were any other rotar it would have been toast.
If you were running a street pad, chances are that the pads could never build enough heat to cause the rotor to form cementite – the iron carbide formation that people often mistake as “warping”. Your pads probably got so hot that it was in was in a perpetual ‘fade’ and could no longer produce any meaningful friction.
I have updated this post to reflect this information.
Thanks for posting!
My car has had the rotors resurfaced 2 times, and I still get a shake while breaking. It seems like light breaking is the worse at highway speeds. Now I’m looking at getting new rotors and pads, you’re description says to use carbon based rotors to slow the cementite build up. Will aftermarket ceramic pads help keep the build up down, or is OEM the way to go?
The carbon based rotors I refer to in the article are the ones found on high end sports cars and cost about $5000 a piece. Those rotors don’t slow the formation of cementite; cementite just doesn’t form because they are not iron based – cementite is an iron compound. So unfortunately, the problem is with the iron itself in typical car rotors and not the pads.
But, high quality rotors and pads can help prevent the problem you’re experiencing. Unless you are driving very hard to the point of fading your brakes, good pads and rotors should not develop vibrations for a very long time… it does seem to happen eventually though.
Personally, I haven’t had any good experiences with ceramic pads. The only benefit I noticed is that they don’t dust like a semi-metallic pad. I can’t say that there isn’t good ceramic pads on the market; but because I have not had a good one, I cannot recommend them.
No luck here with resurfaced rotors. I think the metal has lost its temper.
I am not sure if you know much about heat transfer or energy. If you are worried about your rotors getting too hot under braking, having crossed drilled rotors WILL help cool your rotors. Heat Capacity is the amount of energy it will take to raise a material by 1 Kelvin or J / Kg*K. The heat capacity of air is ~1000 J/ Kg*K depending on humidity while most metals are much less than that. For instance solid Iron ~100 J/KgK. If you have 10000 Joules of energy then it will increase a Kg of air by 10 Kelvin. While for the same amount of Iron it will go up 100 Kelvin! Saying crossed drilled and slotted rotors give no benefits to cooling is completely wrong! In general increasing surface area will help in cooling. Please do some research before posting, you are trying to discredit all the engineers building sports cars. #imtalkingaboutscience
Dan, you seem to be confusing specific heat capacity with volumetric heat capacity. Let’s imagine that a solid iron rotor has 1% of its material removed by drilling. Its heat capacity will drop by almost 1%. The density of iron is very roughly 8 g/cm**3, whereas air’s density at sea level is around 1.2 Kg/m**3. That is equivalent to 0.0012 g/cm**3, or less than 1/6000th of the density of iron. Given your argument that air’s specific heat capacity (energy needed to heat a unit mass) is 10x that of iron, then the air in the holes will have 10/6000 or 1/600 of the heat capacity of the iron that used to fill them (its volumetric heat capacity is very low). Obviously the contribution of the air to the rotor’s heat capacity will be negligible and far less than what the removed iron used to contribute. The heat capacity of the rotor will effectively drop in proportion to the amount of material removed, but since so little material is removed this will not be noticeable.
Of course, in the real world it is not a stagnant mass of air or iron that cools a hot rotor. Instead it is largely the constant replenishment of the air around the rotor with relatively cool ambient air (that, and radiation (ie, glowing) if the rotor is really hot). Even at low speeds, huge amounts of air are flowing around the rotor and carrying off heat. Providing a larger cooling area by drilling certainly *could* improve the rotor’s cooling, though predicting how much would be very hard to do analytically as the air in this region would be very turbulent. If the air is so turbulent that there is little net flow through the holes, then the extra surface area will not help much as the air inside will just get hot. My main point, though, is that air is significant because it’s always in fresh supply, not because a Kg of air can hold more heat than a Kg of iron.
Incidentally, one of the best ways to reduce rotor temperatures is not to drill them, but to install brake ducts. If you read instructions for bedding track or racing pads, they will often advise you to cover up brake ducts, but they will not advise a longer or higher-speed bedding process for drilled rotors versus solid. That suggests that either the manufacturers have overlooked drilling, or they consider it less effective than ducting.
Drilling actually reduces the surface area and mass of the rotor. Slotting increases the surface area of the rotor but reduces its mass.
Steve you may want to review your post as it doesn’t make sense
Dan, I believe you are missing so many other factors. Like you say, “In general increasing surface area will help in cooling.” – key words “in general”.
Now prove to me that cross drilling rotors has a significant effect on cooling. Those holes must help, right? Because race cars have cross drilling.. Oh wait, they don’t.
#I’mcallingyouout
#howaboutyouproveit
I use the race car analogy with my kids. Race cars are the test bed for the best technologies. They get paid for winning. There is a good reason race cars are rear-wheel drive and use solid rotors – because they want to get paid and the money is in rear-wheel drive/solid brake rotors. Drilled and slotted rotors look beautiful and I was going to buy a set for my 4Runner, but after reading this excellent article, I;m buying blanks in about four minutes. Thank you, John Milmont.
So, I just read an article on espn’s web site that states that the system that brembo developed after months and months of research starting with finite element analysis and moving to computational fluid dynamics followed by more advanced and rigorous tests for all the NASCAR teams they have their systems on, have slotted rotors. Hmmm… It also states that in the Martinsville race drivers apply thier brakes every 8 seconds for five hundred laps. Two turns x 500 laps = 1,000 applications per race where the rotors reach 1200 degrees with only 8 seconds to cool off. Pretty demanding. But yeah, NASCAR uses slotted rotors. But wait, they give no benefit, just look cool and no race cars use them. …………
Slotting may have some benefit as it wipes the surface of the pad. It could also possibly increase cF, but, the key words here are “may” and “probably”. Slotting does seem popular these days with race teams that maintain iron rotors, but what exactly are they saying the slots do? I would like to see an objective number on the improvement over a blank rotor. Remember, this is suppose to be a science, and scientific things are measurable.
Wilwood talks a little about slotting in this link:
http://www.wilwood.com/m/techtip/TechFaqAnswer.aspx?id=8&no=2
And those pads will be probably be trashed at the end of the race, too. If the slots are simply to clean the face of the pads for a race environment, maybe it makes sense. But sitting here on my sofa, I’m leaning towards the possibility that they decided to go with slots on the basis of “can’t hurt, might help”. And if the slots actually do keep a pad trimmed (and what? I doubt it.) then it will also be true that pad life will be diminished. Also, slots remove surface area for the pad to press against. If slots gave me 5% more stopping power – nah, they wont. Maybe best in rain, but friction dries pads. Slots don’t dry pads. 🙂 My mountain bikes rotors are drilled and yes for sure that helps braking in muddy, wet weather. But those rotors will never crack from heat and stress, either. Very thin and they cool quickly, but can warp from heat. Composite pads in my mountain bikes.
I would have to disagree with your statement that rotors rarely warp. I have put a dial indicator on numerous rotors in my shop and found them to be warped. I have a 2001 Silverado (bought new) that has warped every set of rotors that I put on it… from OEM, to cheap Advance Auto, to expensive drilled/slotted. The drilled/slotted actually lasted a few years prior to warping, suggesting that it is heat related and they do help dissipate heat better. The original rotors warped within the 1st year. If you haven’t seen rotor warpage with a dial indicator then you haven’t checked many. I once had a new set on a Ford truck that pulsated immediately and were out .005″ out of the box. Drilled rotors do have less surface are, so there probably is a slight reduction in braking performance, but in my case the increased reliability is worth the tradeoff. I got on here because they are warped again and I’m trying to find a good brand that will not warp at all. I have my doubts. I just think they were not designed to be heavy/large enough for the vehicle’s size.
Hello all,
There’s an outfit called the Society of Automotive Engineers (SAE) and here is a comprehensive report they did on this topic:
http://home.wavecable.com/~vtucker/A4/rotors.pdf
Wish I could cut through the 28 pages and provide some profound insight, but I’m afraid you will just need to read it yourself.
Best wishes
Hi Steve,
I was a member of SAE when I was in college. I don’t know what to think of this paper as it raises questions in the area of what the test conditions were. I would like to know what pads were used for his tests and also what car was used. He refers to his personal car as a “performance vehicle” and that’s all. I would like to know if during his test, the rotor had a OEM style heat shield behind it which usually blocks the intake of the rotor. This should effect the results of his crossdrill tests which I feel are very incomplete. Furthermore, he is confusing and not at all definitive on the relationship of crossdrilling and cooling. He says it increases the cooling and heat transfer ability of the rotor, but this raises the question: does the rotor also get hotter than a blank rotor? Heat transfer works both ways… He also has a picture of a drilled hole being blocked with brake debris which would suggest no flow through the holes at all.
Another question I have is: On a car with ducts running directly to the center of the rotor, do cross drilled holes still act as an intake or is air now being expelled through the holes?
I would have liked to seen a test that detailed their setup like this:
Vehicle: 1995 Ford Mustang
Pad compound: PFC01
Rotor diameter: 13″
Rotor width: 1.10″
Duct size: 3″
Duct inlet: NACA Submerged inlet
Rotor backing plate clearance: 0.25″
Drilled hole dia: .125″
Hole density: 1 every 1 inch.
Hole pattern: Interleaved
I think everyone could agree that this would be a lot better.
On the topic of glazing:
Glazing is associated with overheating a given pad compound. Under normal operating conditions, a pad does not glaze. It doesn’t help when the author of the paper does not tell us what pad he was using in his tests. Clearly, as I and many of my readers have experienced, pushing a street pad hard will lead to glazing. But if a race pad is used and never overheated, will glazing be an issue? Also, as far as my experience has been, I have never had an issue with debris on my rotor face; so if my pads don’t glaze and I have no debris issues, is there any benefit to a slotted rotor?
I have stock pads and rotors on 2012 Accord sedan. I had the brajes checked when I started to hear noises. My mechanic said that the pads had started to crystalize, and rotors were”wharped”. He recommended replacing with drilled or slotted rotors. I did some mountain driving this summer. Would this make any sense?
Hello John and others,
So for everyday driving on a sedan with squeaking noise and vibrations when breaking: do you recommend replacing stock blank rotors rather than fancy drilled or slotted rotors? Also, what if we just resurface and change break pads? I understood that just resurfacing is not 100% solving the problem, but seem like a cheaper alternative. But is it worth it?
Drilled rotors do nothing other than look cool. They have no effect on squeaking. There can be a few reasons for squeaky brakes, like caliper issues. But most likely its the pads you are using. If your rotors are still good, get them resurfaced and try a different pad.
A more comprehensive SAE paper on drilled rotor performance:
http://papers.sae.org/2006-01-0691/
Ive turned hundreds or rotors, Ives seen plenty of warp, and that that this guy don’t know crap about it period !
I have a Lexus LX-570, my rotors have gotten warped and discolored on multiple occasions and were replaced with factory rotors. Now after the end of my warranty period I took the car to Midas for brakes and rotors. The initial ones they used lasted less than 3 months. To fix the problem they are suggesting slotted and drilled rotors and carbon pads. Any other suggestions?
Hello John and everyone else,
I have a Lexus LX-570, my rotors have gotten warped and discolored on multiple occasions and were replaced with factory rotors. Now after the end of my warranty period I took the car to Midas for brakes and rotors. The initial ones they used lasted less than 3 months. To fix the problem they are suggesting slotted and drilled rotors and carbon pads. Any other suggestions?
Thank you,
Mark
Slotted and drilled rotors will do nothing to cure this issue. I don’t know how you drive your car, but it sounds like you are very hard on the brakes. Is this happening to all your rotors or just one? If its just one, that would sound like a stuck caliper. If all, sounds like you are really hard on the brakes. If you just are hard on them, then I would look for a different pad. Dont get anything ceramic.
Hello John and Everyone,
This post still seems to be alive so here’s my question. I have a 2010 Mazda CX-9 Touring, and I’ve recently noticed a shimmy in the steering wheel. The issue doesn’t occur under 65mph, but the faster I drive and harder I brake, the more the steering wheels vibrates (most noticeably coming down steep hills at faster speeds). This leads me to believe it is warped rotors… and I never turn a rotor. Always replace as I just don’t think it’s worth the money.
Here’s my question… I’ve been looking at blanks at my local O’Reilly and they offer their “BrakeBest” rotors. $80 for a pair. Where OEM from factory will be $120 each. I did some research and BrakeBest rotors seem to be manufactured by Bosch (correct me if this is wrong). Is this a decent rotor to purchase? Have you heard of anything good/bad on this brand? Do you have a specific brand you would recommend?
Thanks,
Wes
Did you try amazon for rotors? I usually run Centric brand rotors and they have held up well.
Hi there,
I have a 2014 Cadillac CTS-V, the front discs ‘warped’ after less than 12000 miles of driving. However, the car is an automatic, and ambient temperature here in Abu Dhabi is generally over 45°C. The discs were skimmed, but the problem has recurred after only covering another 3000 miles.
The general driving conditions are free-flowing motorways, with the odd few miles in city traffic.
Should the pad compound be changed to reflect the high ambient temperature?
Many thanks
Dean Dupre
I’m not sure if an ambient temperature of 45°C is going to have that much of an effect on brake pads, but it might. Also, I don’t know of any street pad that is made for desert conditions like this. The only high temp option would be to move into a race pad, and those are kinda annoying on the street so they are not really a good idea. You might want to experiment with different pads. I just got Hawk PC (Performance Ceramic) pads and I have been impressed with them on my street car. In fact, this is the first ceramic pad that has ever impressed me.
If you find that only 1 rotor is having this problem, I would check for a stuck caliper. It happens even on new cars.
I’ve read through much of the content here, and was wondering why no one has mentioned how tire rims effect heat dissipation of rotors? Correct me if I’m wrong, but aren’t tire rims in direct contact with rotors, and they too act as heat sinks which draw heat away from rotors? Hub caps can also restrict, or enhance air-flow over rims, depending on their design, helping to dissipate that heat, or contain it. It’s also my opinion drilled rotors have any significant benefit, and the elephant in the room has more to do with airflow over heat-sink components. (Tire Rims)
They surely do, but for a single piece rotor (the type found on typically every car), I have wondered if the cooling effect they have negatively effects the rotors. The issue is that the center of the rotor already heats and cools at a different rate than the surface that the pads touch. The cooling effect of the wheel most likely makes these temperature differentials greater, putting more stress into the rotor. This is an issue because its not uncommon for rotors to crack from all this stress, even if they are not cross-drilled.
Hello John, and others. I’d like to say that I agree 100% with what you’ve said here. I don’t have an SAE certification, or an automotive degree if that even exists, but I do have real world experience. I brake hard, and I’ve used slotted, drilled, slotted and drilled and I’ve noticed that if there is a difference in performance from the fancy rotors versus blanks than it’s either negligible, or so insignificant that it’s not noticeable. With all the physics jargon thrown out on this post I’ll say that the best way to prove something is to go out and test it, not throw numbers, equations, and scientific lingo around. But on a lighter note, I’m still grinning about the argument brought up about NASCAR using slotted rotors during a race. I’m grinning because I didn’t realize NASCAR was racing. I wouldn’t call driving in a counter clockwise circle for hours a motor sport. I feel NASCAR is for the racing flunkies, and for the real race car drivers, to get ready for retirement.
So I guess Talking about braking from a sport that actually uses the brakes is somehow not relevant? Seriously if you’re saying drag racing counts where you only use your brakes once (often with a parachute back-up) I feel like the point is missed.
What works best multiple times…I would hate to round that 100th turn with no brakes. lol
I used to work in NASCAR, as an aerodynamicist. It is absolutely racing, and while all racing formulae are to some degree contrived I’d agree that circle-track racing is more contrived than most. That said, just like drag racing, the talent is finding and staying on the edge of the envelope on any given day. (And in all the other aspects on and off the track of course.)
As for this nonsense: “the best way to prove something is to go out and test it, not throw numbers, equations, and scientific lingo around”, insomuch as it merits a response: neither on their own are sufficient. Science is broadly a rigorous method of not fooling yourself, and you are always the easiest person to fool. Practical experience is a critical part of doing good science. “Jargon”, when used properly, is a necessary way of being precise and concise to avoid ambiguity.
Cross drilling rotors is done to reduce their mass – See Newton’s Second law of physics.
It is the same thing as putting lighter rims and tyres on your car or lightening your flywheel – rotational mass stores inertia, removing rotational mass frees up torque at the expense or power stored in inertia.
Reducing the weight of the spinning components of your drive line will increase your acceleration as less torque will be required to accelerate, so the torque your engine produces (your power band) will be larger. The downside will be your fuel millage – without the stored energy of the extra inertia, your car will slow down faster when coasting.
It is this last point that makes lightening your rotors with holes seem like the smart thing to do. However, reducing rotational mass elsewhere and having more contact pad surface on the brakes usually yields better results with out the issues already mentioned.
Rotational mass has a ration of anywhere between 7:1 – 11:1 over static mass depending on who knows what…
So, for the sake of argument, lets say that cross drilling removes a quarter of a pound from each rotor:
.25 x 4 x11 = 11lbs of weight from the car. Hardly worth the issues noted above.
John Milmont,
If drilled and/or slotted rotors are worthless ,why do car companies, race teams ect still defy all your “uhmmm wisdom”?
The only thing that ever stopped a vehicle of mine from warping the front rotors, that came with horribly undersized front brakes was, powerstop replacements (drilled and slotted). schools out.
You should probably read my post before commenting. I already explained why car companies put them on street cars. I also said that i was not aware of any professional races teams that run drilled rotors. So please show me these race teams that are running them. Also, as far as slotting, I said I was not clear on its benefits. But I wouldn’t be surprised if even pro teams put slots on the rotors for some aesthetic value. Slotting does not weaken the rotor like drilling does and may provide some benefit in clearing the rotor surface from debris. Furthermore, I doubt you are telling me the whole story with your experience. I’m guessing that you used different pads with those replacement drilled rotors you are talking about; and its the pads that cured your ‘warping’ issue.
When you speak of “race teams” you are also talking about EXTREME temperatures where the rotors glow orange/red plus you have the addition of cooling fans. Not really Apples to Apples when compared to hard street driving. It is highly unlikely that anyone driving on the street will ever be breaking under the same conditions.
I work as a machinist with extensive training in metallurgy…many other things need to be considered than just “mass” and “pad contact surface area”. I have seen posts only referring to “surface area” in that respect…Air for cooling contacts more area when drilled and slotted.
Wow. All this BS about how rotors transfer heat and deform but not a single mention of metallurgy. Steel is not Fe and it’s not Al, either. I understand rotors are made in certain grades of steel, but not all steel is the same and manufacturing process plus blend has a lot to do with product performance. I’ve had rotors made overseas that “warped” in three weeks whereas the same item made under better manufacturing standards lasted indefinitely. A true applied test would take identical rotors from the same batch, same manufacturer, same foundry and apply cross drilling and/or slotting to the same rotors. Then run them on identical cars under similar conditions.
On another note, where can I read the SAE articles without paying through the nose?
Yes, I think this is an often overlooked aspect.
The issue is that people have factory or other cheaper rotors and they warp or crack or whatever and then someone tells them to buy fancy slotted rotors, which turn out to be much better and then they come to the conclusion that the slots must be the only difference and therefore the slots are the key.
What they are forgetting is that they likely just purchased rotors of an overall higher quality in terms of materials and manufacturing and that’s what’s making the difference.
I used to be on the slotted bandwagon until I realised how good heavy duty plain rotors were and did some more thorough and realistic thinking about how likely it is that the slots and/or holes would be a noticeable benefit.
I’ve done track days where I had factory calipers with high end plain rotors and pads and a number of other people (with the same model car and similar power) had fancy Brembo calipers and slotted and/or drilled rotors and mid level pads and I could out brake them all day. i could out brake them all day with practically zero fade.
My performance was primarily due to the very high temp pads. high performance pads are tougher on rotors so you need higher quality rotors, which like you say, are often slightly different alloys than cheaper rotors. Some of these different alloys are also claimed to have preferable heat transfer properties but my opinion thats probably mostly marketing spin also.
Next to pad choice and the overall mass and hardness of the rotors, slotting or drilling a rotor would have such a negligible difference in performance ether way that I could never justify the additional cost let alone justify any potential reduction of the structural integrity of the rotors or any increase in wear on my brake pads (good pads aren’t cheap).
Steel? Are you kidding? Brake rotors are NOT made of steel. They’re made of grey iron, G3000 to G4000 usually. That’s why they need to be coated in order to prevent rust. Cross-drilled rotors are superior to blank rotors in bite, brake fade, and lower temperatures across a certain range, as proved in the SAE paper “The Effect of Rotor Crossdrilling on Brake Performance 2006-01-0691”. F1 rotors are not drilled because they use carbon ceramic rotors which require a lot of heat to function optimally, these rotors are designed to hold on to heat rather than dissipate them. Look at images of F1 brake rotors and you’ll see the even the vanes are much smaller than your standard Civic ventilated rotors.
In street applications, cross-drilled rotors are superior. In racing applications, it depends on ruleset, as they are subject to certain rotor diameter and weight. Most of the times, maximum heatsinking is preferred over more heat dissipation, so blank or slotted rotors are the safer choice. In touring races, cross-drilled rotors are used often as braking points are followed by high speed straights, which makes greater use of airflow through the brake rotor.
Can you show me a professional team running x-drilled rotors?
So, I drive an ’08 Lexus GS350. I drive it the way I believe it was meant to be driven which means I had to have the transmission & AWD transfer case replaced at exactly 100K. Good on me eh? I’ve been through several sets of brakes including rotors. While this thread has been fun to read, the road tells the real story. I went from factory blanks to slotted only and then to slotted & drilled. I am heading back to high quality blanks with The best ceramics I can find. I change 100% of the fluid every time I do the brakes. Interesting that just today as I was disassembling the RR wheel to replace the bearing assembly and I found my rotor looks precisely like the image above which was a bit of a shock. Applied physics lessons aside (but truly appreciated), Mr. Milmont is correct.
I have read some different articles on this. There was a question in a post about the purpose of slotted rotors. My finding showed the purpose was to release gasses produced by the brakes. By releasing this gas the pads bite on the rotor instead if this cushion of air. They also help in wet conditions to allow water to push out again giving the pads a better surface to bite on.
As far as my two sense. Ad far as drilling a rotor in rages to heat. I don’t believe the question is surface area dissipating heat. From my own experience the holes rather give the heat a place to go. In other words as the heat builds in rotors the heat has the holes as vents. Now I have no scientific proof of this however I did talk to some experts in the auto industry and that’s what the conversation was. Again these are opinions I heard as I am no expert. As far as that picture of the rotor on top of page I would guess it would be cracked. It looked like someone stood on the brakes for hour on that to the point it wore the rotor to no end. So regardless of being drilled that rotor went thru hell. Thanks
Hi, this is a great article. I replaced my 2006 Lexus IS 250 front pads and rotors with EBC grey iron rotors (slotted but not drilled) and with ceramic pads(EBC red stuff). This was probably in around 2009. The biggest advantage I found is that there was a great reduction in dust created by the ceramic pads compared to the factory pads and rotors, and pad lifespan. A few years into them I noticed vibration while braking from highway speeds. This past spring 2016 I noticed that the car now vibrates above 60km/hr and at 100km/hr the rearview mirror is blurry, so I guess it’s finally time to change them. The pads I was told still have 50% wear on them but the rotors sound to have warped as you say. Well can’t say I didn’t get my money’s worth. Thanks.
Hi, this is definitely a great article. I replaced my 2006 Lexus IS 250 front pads and rotors with EBC grey iron rotors (slotted but not drilled) and with ceramic pads(EBC red stuff). This was probably in around 2009. The biggest advantage I found is that there was a great reduction in dust created by the ceramic pads compared to the factory pads and rotors, and pad lifespan. A few years into them I noticed vibration while braking from highway speeds. This past spring 2016 I noticed that the car now vibrates above 60km/hr and at 100km/hr the rearview mirror is blurry, so I guess it’s finally time to change them. The pads I was told still have 50% wear on them but the rotors sound to have warped as you say. Well can’t say I didn’t get my money’s worth. Thanks.
I have a 96 Mustang GT road car slightly modified. I will choose slotted based on this article. The only goal is to have the best brakes possible in an emergency situation. The choice I have from the supplier is stock, slotted or cross drilled.
I drive a Jaguar XKR in the UK. I have vented cross drilled rotors. All the holes are full of pad debris. They look cool on the Jag but as all the holes are blocked I fail to see what positive affect the holes could have son cooling. The amount of metal rom moved by the wholes relative to the complete rotor is tiny. Weight saving or change to heat capacity must be minimum.
The rotors and pads are worn and need replacing but I will be replacing them with quality but blank (solid) rotors.
I drive a Jaguar XKR in the UK. I have vented cross drilled rotors. All the holes are full of pad debris. They look cool on the Jag but as all the holes are blocked I fail to see what positive affect the holes could have on cooling. The amount of metal removed by the holes relative to the complete rotor is tiny. Weight saving or change to heat capacity must be minimum.
The rotors and pads are worn and need replacing but I will be replacing them with quality but blank (solid) rotors.
I drive a Jaguar XKR in the UK. I have vented cross drilled rotors. All the holes are full of pad debris. They look cool on the Jag but as all the holes are blocked I fail to see what positive affect the holes could have on cooling. The amount of metal removed by the holes relative to the complete rotor is tiny. Weight saving or change to heat capacity must be minimum.
The rotors and pads are worn and need replacing but I will be replacing them with quality but blank (solid) rotors. I will report back if unitive a difference.
I drive a 2011 Altima SR…six speed and fun to drive. Are the OEM rotors cut thinner as I was only able to get two resurfacing turns done in 77k miles!
Planning to replace them with OEM but Nissan wants $130 each for front rotors and $99 for pads. I work in Austin TX and do a great deal of stop and go driving…also drive our 80 mph toll road often so driving good distances at 85 mph is not uncommon.
I drive a 2011 Altima SR…six speed and fun to drive. Are the OEM rotors cut thinner as I was only able to get two resurfacing turns done in 77k miles!
Planning to replace them with OEM but Nissan wants $130 each for front rotors and $99 for pads. I work in Austin TX and do a great deal of stop and go driving…also drive our 80 mph toll road often so driving good distances at 85 mph is not uncommon. Had issue trying to post and hoping it works this time.
….any suggestions on good OEM quality or better replacement kits?
I use centric rotors and get them on Amazon. They have worked great so far, even on my race car.
An excellent read.
I think most forget that: drilling/slotting/ducting aside, it’s critical to choose correct and good quality materials appropriate for the application.
As far as the average driver can take their daily on the road in terms of brake abuse: the single biggest difference in performance will be from pads. Also, putting our egos aside: we’re not race drivers, so our perception of brake performance is inadequate at best.
I just changed the front rotors only on a Volvo XC90. Rotor were factory blanks and I replaced them with “cheap” drilled slotted eBay specials. Old rotors mic’ed good but were “warped”. Brake thumping is gone now and the pedal weight when stopping is dramatically reduce (even my wife noticed and is thrilled). I could care less about the “science” behind them just very happy with the results.
I drive a 2010 Peugeot 207 CC (don’t laugh, it’s a lot of fun for a small car) but under braking I get a huge amount of pulsing, almost like the ABS is kicking in except slower, plus uneven grab at different speeds under the same brake pressure. I’ve just watched a Youtube vide of someone replacing rotors and pads and it looks like it’s within my skill set (after buying a few more tools), but money’s tight and I need to shop carefully. Am I best off replacing pads, rotors, or both? Back ones only or front too? I don’t drive over 120kph so performance parts aren’t an issue, but I do a stop-start round-trip commute of 60km daily.
@John Milmont – very well written article, found it via Google after researching plain or slotted rotors on eBay. Thanks!
The pulsing is coming from the rotors – what you should be interest in is how it got that way. There is a few reasons why this happens, but it does happen naturally over time. Over time, rotors rust (especially if you live in an area with snow and salt) and they always rust at a different rate under the pad area. This creates an uneven surface which you feel as pulsing. This is probably the most common reason for pulsing in everyday cars.
Because you want to save money, I would start by replacing the front rotors and pads first. Then, see how the car is after that. If its still happening, then do the rears. Its always a good idea to do the brake fluid too since its probably been in there since the car was new.
Great article but I have to take issue with this:
“You will hear small metallic pings and pops as the rotor cools unevenly. What you will be hearing is the sound of the cracks forming….”
Pings and pops come from many parts that are differentially heated and cooled. My solid-rotored E63 M6 was pinging like crazy after coming back from a hard drive recently. Do heat-induced cracks even happen all at once, or grow slowly over time without a sound? I’m not sure, but you can hardly assess damage from normal heat pings. The damage probably occurs immediately after a braking events when airflow at speed cools the rotors far more rapidly than stationary convection.
So, You do not recommend Ceramic pads, or cross drilled rotors? I replaced my factoy brakes with cross drilled and EBC Red ceramic pads. Broke them in proper( Most people don’t know how to properly break in or “seat” pads) did all this 5 years ago, never had a crack. This brake upgrade stopped the car hot and cold much shorter distance than original. just now replacing w slotted / cross drilled and new ceramic pads. I am a true believer in ceramic pads. I have run many rallyes with this setup and had no problems from the braking system. https://ebcbrakes.com/product/redstuff-brake-pads/
356 hp 08 jetta 2.5 turbo.
So, You do not recommend Ceramic pads, or cross drilled rotors? I replaced my factoy brakes with cross drilled and EBC Red ceramic pads. Broke them in proper( Most people don’t know how to properly break in or “seat” pads) did all this 5 years ago, never had a crack. This brake upgrade stopped the car hot and cold much shorter distance than original. just now replacing w slotted / cross drilled and new ceramic pads. I am a true believer in ceramic pads. I have run many rallyes with this setup and had no problems from the braking system.
356 hp 08 jetta 2.5 turbo.
Ferritic Nitro-Carburizing Brake Rotors are on my 2014 Malibu and I can honestly say that with they have not warped whatsoever and I have 65000 miles on them.
https://www.acdelcotechconnect.com/pdf/MarApr_2012_TechCONNECT_R1.pdf
Y’all need to Google “Ferritic Nitro-Carburizing (FNC) Brake Rotors” … I can’t post the ACDelcoConnect PDF file because this site thinks its advertising or spam, but the Google result will have that at the top. They came with my 2014 Chevrolet Malibu and I can honestly say that with 65K miles I have completely smooth brakes with no warping or vibration. It’s amazing. OTOH, my wife’s Town & Country minivan, even with the Mopar rotors and brake pads only last 25K miles.
Y’all need to Google “Ferritic Nitro-Carburizing (FNC) Brake Rotors” … They came with my 2014 Chevrolet Malibu and I can honestly say that with 65K miles I have completely smooth brakes with no warping or vibration. It’s amazing. OTOH, my wife’s Town & Country minivan, even with the Mopar rotors and brake pads only last 25K miles.
https://www.acdelcotechconnect.com/pdf/MarApr_2012_TechCONNECT_R1.pdf
Y’all need to Google “Ferritic Nitro-Carburizing (FNC) Brake Rotors” … They came with my 2014 Chevrolet Malibu and I can honestly say that with 65K miles I have completely smooth brakes with no warping or vibration. It’s amazing. OTOH, my wife’s Town & Country minivan, even with the Mopar rotors and brake pads only last 25K miles.
https://www.acdelcotechconnect.com/pdf/MarApr_2012_TechCONNECT_R1.pdf
You are defensive and lazy. Use goggle and do do the work yourself you may learn something in the process. You are not an engineer, we have explained the facts to you, but we can not understand them for you, that is called learning.
I would disagree with the statement that round holes in rotors are “stress risers”. They are usually associated with sharp inside corners (like the inside corners of the slots in rotors). If you punched square holes in the rotor, each inside corner would be a stress riser. If you had a rod that suddenly went from 1″ dia to 1/2″ dia, that step would be a stress riser. That is why you would change dia. gradually (taper). So, I don’t think a round hole would be a stress riser in a rotor. By the way, I drive a BMW. It came with blank rotors from the factory (no holes), and I replace them with OEM blank rotors.
John M,
I am an engineer, and I know or understand 99% of what has been discussed… This is the best write up on the issued of enhanced rotors and warping I have read so far. Kuddos! I agree with 99% of what you have said… but I just have one last question… Its the simpler question….. Since my 76 Nova and my 72 Cutless, I have not owned an American Car that doesn’t suffer from “warped” rotor syndrome!! Horrible! And ever since I have been on a crusade to find the holy grail of rotors.. No luck yet, and no expertise that is consistent as to what to do or what to buy… Thus the simple question for you: What is the best rotor (type or Brand or both) to buy? And what is the latest on your Hawk ceramic pads? My 2014 Impala needs rotors and pads in the next month. If you can help that would be great
(Oh by the way everyone, anyone can get a paper or report to say anything they want!! So just because it has SAE on it, or came from their library does not mean it has any validity! And any report or paper that fails to list assumptions and all variable values, and follows the general scientific method, fails on the first word!! (John has it right) Only Peer reviewed material carries any amount of respect and validity)
Darshan,
I dont think the issue is your rotors, its most likely the pads. I have found that a lot of pads from local parts stores are pretty crappy and tend to create pulsing brakes quickly. I’m really happy with the hawk PC (Performance Ceramic) pads I have. I have had them on my car for I think 3 years now and they are still very smooth. I’m totally shocked and impressed with them. The PC compound from hawk is one of their newer compounds. I was not impressed with their HPS pad which they have had for a long time. I was actually so disappointed in those i took them off my car and sent them back. Historically, Hawk compounds have not been very good, but it looks like these new pads are changing that.
SP Drilled , are on my W-body and all pluses NO VIBES 75kmi little pad wear too.
Very educational exchanges. I chased down more opinions on rotors and have decided on plain ones, and on Centrics, based on your recommendations and Amazon reviews. I also have been chasing down prices. Amazon’s parts finder for my 2002 Base RSX SUCKS! and gave me the wrong part number for the front Centric rotors and a $53.54 price each. So far, carid.com has the best deal at $27.29 each. Amazon had a price of $73.43 for the front Hawk PC pads, also based on your recommendations. So far, various websites have them at prices of $36, 40, 44, 44, and $69. One concern, however, is that the four cheapest sets are from websites ending in “.top” and “.xyz”. Wikipedia lists the .top domain as apparently legit, but another source talks about scams on that domain. I suppose I’m protected through my credit card company or Paypal, whichever they accept, but I’m hesitating a bit. Anybody know anything about those domains or any other strange ones? This has been an all-day project, and I thank you for pointing me in the (hopefully) right directions.
why does every street bike have drilled slotted rotors then
You answered your own question. Because its a “Street Bike”. Check out a bike from MotoGP.
Wow, rear brakes ARE slotted and front is not because they are carbon! I resurfaced many rotors and most were warped. Dont know how you check or you need to check your tools.
I have a 07 saturn vue replace front brakes an rotors about 3,000 miles ago. When the car is cold and driving slow brakes are fine; but on the highway, it feels like the rotors are warped. Can i get away with just up grading the pads .
It sounds like one or more of your calipers are seized. Sadly, this tends to happen a lot with slider type calipers, the kind that are on your VUE. Not only will the rotors need to be replaced, but the calipers will need to be serviced. Whats most likely happening is that the seized caliper is causing the pads to drag an inappropriate amount causing too much heat buildup. The overheating causes the problems described in the article…
Solid article. Driving a 2015 Jetta TDI with solid rear discs, been dying to get ventilated as I have at least a 40/60 brake dispersion front/rear – sometimes swear its 30/70, dust builds first on rear. Point, I have 23k on all 4 rotors/pads, solid OE spec etc. Solid rotors in back have dark even line in middle of contact patch- 1/2 inch polished inner and outer portion of contact. My rotors are one time use parts (found that out the hard way). Would my issue solely be on the pad side of things and try replacing only the pads, or is this a heat issue and try to avoid this with a slotted solid disc with performance ceramic pads?
This is a very interesting conversation. I would like to add something that seems it was not mentioned and that is leased vehicles. I have leased for decades, all Lexus. Since the second gen Lexus IS, I have had them. And every 15K miles or so (about half way of the lease) I have to replace the front brakes (and maybe the pads on the back). I live in Miami FL where it is hot most of the year but then it can rain at any time and water is very cold from that rain. I understand very well the pros and cons for each option when it comes to rotors and pads, but I find that for a lease vehicle, since I don’t have to worry about it for more than three or four years, that I am better replacing the stock rotors for a set of either crossed-drilled or the combination of crossed-drilled and slotted. Why? Because in my case, the replacement will last me for one and a half to two years before I return the vehicle and get a new one and in my experience, those work best for the rain and they do avoid warping when it is very hot, I have been driving for an hour or so (brakes are burning hot) and it starts to rain “cats and dogs” out of nowhere, flooding streets in a matter of 10 to 15 minutes. I do not care if the brake life will be short because of cracks (if they ever happen), but I do care about being able to brake in such wet situations, and crossed-drilled are the best. I do buy good quality from good brands, not the top of the line (no need) but not cheap ones either. All the physics, math, real life testing and opinions are good to read and understand, but when it comes down to reality, each case is different, and in my case, all the cons for those type of brakes are irrelevant as most likely, will not affect me and I will be getting a new vehicle before anything noticeable could happen to the brakes. Cheers.
Science vs real life.
I greatly appreciate this artical. However this is my PERSONAL experience.
I bought a complete set of slotted and drilled black anodized rotors and ceramic pads for my 2011 F150 FX4 5.0 4×4 from Amazon.
I spent a whopping $325 for all four.
I did not expect much for the price. Purchased because they were cool looking.
I did not use the ceramic pads which came with the set, I used Wagner Theroquiet instead.
I drive my truck like a race car all the time. I am very hard on it and the brakes. I was going throught front rotors and pads once a year at least. I was using OEM rotors.
Since I made the switch over 4 years ago I have not needed to replace rotors and just recently replaced the pads.
The truck stops quicker and all parts last much longer. The only thing I have done every six months is to have the tires rotated and get the brakes cleaned up and pins re-lubed.
Made a believer out of me.
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