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Thread: Slotted versus Drilled Rotors

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2020-08-16 15:09:41
#1
Slotted versus Drilled Rotors
This content was originally posted in the a non-public section of the forum where non-members can't see it. I'm reproducing it here for reference outside of the forum.




This isn't just my opinion. I don't shun holes in rotors and promote slotting because it makes me feel warm and fuzzy inside.

Source 1:
Originally Posted by Superchargers Online
Contrary to popular belief, they don't lower temperatures. In fact, by removing weight from the rotor, the temperatures can actually increase. The holes can actually create stress risers, allowing the rotor to crack sooner...

Slotting rotors, on the other hand, might be a consideration if your sanctioning body allows for it. Cutting thin slots across the face of the rotor can actually help to clean the face of the brake pads over time. This, in turn, helps to reduce the “glazing” often found during high-speed use, which can lower the coefficient of friction.


Source 2:
Originally Posted by Arret Brakes
Which one is better? This is a common question and naturally, each of them have their benefits and drawbacks. For any performance applications we recommend our AB SELECT rotors. Slots clean the brake pad surface which helps to increase brake "bite". Drilled rotors have the same benefit of cleaning the brake pad surface, but under heavy braking, such as a racing environment they are prone to cracking. For most people drilled rotors provide the desired look yet we only recommend them for street applications with mild braking situation. Slotted rotors are also a good addition to any vehicle that is used for towing, as the benefit is the increased "bite" that you get from the slots.


Source 3:
Originally Posted by Darrick Dong
Anyone that tells you that drilling makes the disc run cooler is smoking crack.


Source 4:
Originally Posted by Power Slot
At one time the conventional wisdom in racing circles was to cross-drill brake rotors to aid cooling and eliminate the gas emitted by brake pads. However, today's elite teams in open wheel, Indy and Trans Am racing are moving away from crack prone, cross-drilled brake rotors in favor of rotors modified with a fatigue resistant slotting process.


Source 5:
Originally Posted by Stop Tech
StopTech provides rotors slotted, drilled or plain. For most performance applications slotted is the preferred choice. Slotting helps wipe away debris from between the pad and rotor as well as increasing the "bite" characteristics of the pad. A drilled rotor provides the same type of benefit, but is more susceptible to cracking under severe usage. Many customers prefer the look of a drilled rotor and for street and occasional light duty track use they will work fine. For more severe applications, we recommend slotted rotors.
(Note that even though Stop Tech sells both drilled and slotted rotors they do not recommend drilled rotors for severe applications.)

Source 6:
Originally Posted by Wilwood
Q: Why are some rotors drilled or slotted?
A: Rotors are drilled to reduce rotating weight, an issue near and dear to racers searching for ways to minimize unsprung weight. Drilling diminishes a rotor's durability and cooling capacity.


Source 7:
Originally Posted by Waren Gilliand
If you cross drill one of these vented rotors, you are creating a stress riser that will encourage the rotor to crack right through the hole. Many of the rotors available in the aftermarket are nothing more than inexpensive offshore manufactured stock replacement rotors, cross drilled to appeal to the performance market. They are not performance rotors and will have a corresponding high failure rate.

(Warren Gilliland is a well-known brake engineer in the racing industry and has more than 32 years experience in custom designing brake systems ...he became the main source for improving the brake systems on a variety of different race vehicles from midgets to Nascar Winston Cup cars.)

Source 8:
Originally Posted by From Baer
What are the benefits to Crossdrilling, Slotting, and Zinc-Washing my rotors? In years past, crossdrilling and/or Slotting the rotor for racing purposes was beneficial by providing a way to expel the gasses created when the bonding agents employed to manufacture the pads...However, with today's race pad technology, 'outgassing' is no longer much of a concern...Slotted surfaces are what Baer recommends for track only use. Slotted only rotors are offered as an option for any of Baer's offerings.


Source 9:
Originally Posted by Grassroots Motorsports
Crossdrilling your rotors might look neat, but what is it really doing for you? Well, unless your car is using brake pads from the '40s and 50s, not a whole lot. Rotors were first drilled because early brake pad materials gave off gasses when heated to racing temperatures, a process known as "gassing out." ...It was an effective solution, but today's friction materials do not exhibit the some gassing out phenomenon as the early pads. Contrary to popular belief, they don't lower temperatures. (In fact, by removing weight from the rotor, they can actually cause
temperatures to increase a little.) These holes create stress risers that allow the rotor to crack sooner, and make a mess of brake pads
--sort of like a cheese grater rubbing against them at every stop. Want more evidence? Look at NASCAR or F1. You would think that if drilling holes in the rotor was the hot ticket, these teams would be doing it...Slotting rotors, on the other hand, might be a consideration if your sanctioning body allows for it. Cutting thin slots across the face of the rotor can actually help to clean
the face of the brake pads over time, helping to reduce the glazing often found during high-speed use which can lower the coefficient of friction.
While there may still be a small concern over creating stress risers in the face of the rotor, if the slots are shallow and cut properly, the trade-off appears to be worth the risk. (Have you looked at a NASCAR rotor lately?)


Source 10:
Originally Posted by AP Racing
Grooves improve 'cleaning' of the pad surfaces and result in a more consistent brake performance. Grooved discs have a longer life than cross-drilled discs.


Sources 3-10: What Kind of Rotors Should I Get?
2020-08-18 10:12:27
#2
Meanwhile, we stick with solid rotors thanks! They don't crack and degrade as fast and don't wear out brake pads as fast. We stop just fine, thanks.
2020-08-18 10:28:32
#3
^^^^ LIKE ^^^^
2020-08-18 21:30:00
#4
From my experience, and the majority of reading on the subject, slotted rotors extend pad life over blank rotors.
I guess I have to do another deep dive to dispel another braking myth?
Why is this always my job...

I also run blank rotors, but that's beside the point. This thread is about slotted versus drilled.
Last edited by BenFenner on 2020-08-18 at 21-31-56.
2020-08-19 09:21:54
#5
Originally Posted by BenFenner
From my experience, and the majority of reading on the subject, slotted rotors extend pad life over blank rotors...


Does not compute.
2020-08-19 11:04:01
#6
Long story short, the slots continually compress the terminal layer of the pad, making it slightly more dense, and slightly more resilient.

I can't be the only person doing proper research around here. Do your own. Question your assumptions. Be better.
2020-08-20 12:28:25
#7
Originally Posted by BenFenner
Long story short, the slots continually compress the terminal layer of the pad, making it slightly more dense, and slightly more resilient.

I can't be the only person doing proper research around here. Do your own. Question your assumptions. Be better.


My research indicates that all those edges dragging across the pad surface cause additional wear, but I'm not a doctor, so.
2020-08-22 20:22:32
#8
There is something pondering me now I read this, I have stock rotors and replaced my old generic pads because I lost one pad, (yes that is possible) and I bought some Febi Bilstein pads since price compared with generic pads was negligble and this brand suggested their pads would in no way add to noise which I also had a bit. The pad was slotted and some claims made there but within 2000 miles a wheel bearing gave up so I took everything off. Both pads were it was slotted totally filled up with debris, does anyone know how that was possible? It was easy to remove so I did but I didn't check the other side. Will do soon because that wheel bearing went out also ( less than 10k miles, top brand :/) but how come that slotted part of the pad becomes filled up with I assume brake dust?
Last edited by richardwbb on 2020-08-22 at 21-33-53.
2020-08-22 22:00:32
#9
You're way off topic for this thread.

The slot in a pad will fill up with debris and dust because it's a perfect place for that stuff to collect. This should not be surprising.
2020-08-23 10:01:46
#10
Okay I'm sorry. I should stop worrying a bit more I suppose. Maybe I should shift to the stock rotors are fine side. My slotted and drilled rotors turned out one to stay noisy. Out of ten people in a group buy I have had the noisy ones. Please delete my posts
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