Drilled or slotted rotors still relevant?

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J. A. Rizzo

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I've been told by a few people that on modern cars with ceramic brake pads, there's really no benefit to using drilled or slotted rotors any more. The reasoning is that ceramic pads don't outgas or dust up like semi-metallic or organic pads did, so the slots/holes aren't removing any gases or dust that prevent full contact with the disc surface.

If that was the case, then I would think with ceramic rotors, they would just serve to reduce the disc surface area and total braking capacity. Anybody have any definitive sources on this?

I was just wondering if it would be worth replacing the vented, flat-surface rotors on my SUV with drilled or slotted rotors to get a little better braking performance while towing a trailer. But then I was told that my Honda Pilot has ceramic pads, so I shouldn't do that.
 
You will get absolutely no benefits from drilled or slotted rotors on your street-driven car. None whatsoever. What you hear is correct.
 
Drilled and slotted rotors make more noise, more dust, wear pads faster, retain dirt and water in the grooves, are more expensive, are very tough to re machine, and often weight less [this is a double edged sword, however - i LIKE heavier brake rotors].
Plain iron is best.
This does not mean common internally vented - that is good -- I refer to the pad surface area.
 
Slotted has some advantages. If nothing else it keeps brake pad buildup to a minimum and a fresh surface all the time.

Drilling is kind of hit or miss. If done right it does not compromise reliability. I have slotted and drilled 13" rotors on my TL and they work fine even with many hard stops back to back from 120mph. Drilled can work better in rain.

It's hard to say anything about the cooling benefits. These 13" rotors run 100-150 degress cooler than the stock 11.8" rotors during normal driving. In fact they run cooler than the rears unless I'm doing a lot of hard braking. I can't say how much of that is due to the size and how much is the drilling but I'm sure most of it is from the size. Temps are cooler right around the holes FWIW but I don't know if that's a good thing to have different temp on the braking surface.
 
Keep in mind that lots of drilled rotors are drilled after casting, which creates lots of little stress risers. You wind up with a weaker brake pad that costs you more money. Ironically these drilled rotors are often worse with heat than a solid rotor!

Drilled & slotted rotors also have a cheese grater effect on pads. So everything wears out faster.

Stick with plain internally vented rotors. If you need more stopping power, try a premium rotor & pad, keep the brake fluid fresh and anticipate stops better.
 
Originally Posted By: mechtech2
Drilled and slotted rotors make more noise, more dust, wear pads faster, retain dirt and water in the grooves, are more expensive, are very tough to re machine, and often weight less [this is a double edged sword, however - i LIKE heavier brake rotors].
Plain iron is best.
This does not mean common internally vented - that is good -- I refer to the pad surface area.


I've seen both sides to the wear issue. Some people see no additional wear when going to slotted rotors of the same size with the same pads. I also prefer a heavier rotor, mine came drilled but the replacements will only be slotted.

There is some noise but it's only heard under heavy braking. You can hear a whirring from the slots but you never hear it under normal driving.

I can't argue, this thing is running 140 degree rotor temps on a 70 degree day. Rears run about 170.
 
Originally Posted By: scurvy
Keep in mind that lots of drilled rotors are drilled after casting, which creates lots of little stress risers. You wind up with a weaker brake pad that costs you more money. Ironically these drilled rotors are often worse with heat than a solid rotor!

Drilled & slotted rotors also have a cheese grater effect on pads. So everything wears out faster.

Stick with plain internally vented rotors. If you need more stopping power, try a premium rotor & pad, keep the brake fluid fresh and anticipate stops better.


There are many that still make quality drilled rotors. You guys are making blanket statements here regarding reliability and pad wear. In some cases it's try, in others it's not. I have $2,000 in front brakes, it's not some cheap kit that's going to come apart on me. I don't recommend the $100 drilled rotors.
 
Originally Posted By: BobsArmory
As far as I know the drilled and slotted rotors are there more for weight reduction and cooling. Here is a cool site to look at for the brake crazy guys out there.

http://www.frozenrotors.com/


+1

If you really feel like spending a bunch of money on rotors, go with a set of cryogenically treated rotors - they'll tend to resist warping and last longer.
 
slotteds were supplied via factory TSB for my car as they simply spec'd a WAY too aggressive pad for the factory Brembo setup. But how many luxury sedans have 4 pistons at every corner?

They make a little noise when you brake vigorously, otherwise they are great.

But for any normal street driven car slotted/drilled are bling. And how many here have seen the drilled crack at the chamfer?

I recommend Dave Zeckhausen at Zeckhausen Racing

http://zeckhausen.com/

he's a great guy, tons of experience and knowledge.
 
Originally Posted By: BuickGN
There are many that still make quality drilled rotors. You guys are making blanket statements here regarding reliability and pad wear. In some cases it's try, in others it's not. I have $2,000 in front brakes, it's not some cheap kit that's going to come apart on me. I don't recommend the $100 drilled rotors.


While I don't disagree with your statement that "There are many that still make quality drilled rotors" it certainly leaves room for my statement that there's a lot of junk out there for those of us that won't spend two large on front brakes alone. I certainly wouldn't spend that much on brakes, but my cars are daily drivers & family haulers, not weekend track cars.

So I wholeheartedly agree I'm making a blanket statement - for the kind of brakes 99.9% of people will be buying.
 
There never was any real relevance for driled or slotted rotors in typical daily use cars, beyond something like a very benign slotting, similar to the ATE powerslot rootors... and there the "slot" was not in the typical shape/form, and was as much a wear indicator as anything else...

The main thing for most applications is thermal mass. Brakes arent about cooling, they arent about gassing in typical applications, they are about being an efficient sync of thermal energy that is converted via the friction material. A drilled rotor is a tradeoff between thermal mass to accept heat, versus a tiny bit of extra surface area, which may add to cooling by a marginal amount.

Slots scrape the pads, and some say this is good. THey also supposedly allow for some release of gas as well. THey do this without removal of lots of mass, which is good, but it is still doubtful that the average user will notice.
 
Originally Posted By: J. A. Rizzo
I've been told by a few people that on modern cars with ceramic brake pads, there's really no benefit to using drilled or slotted rotors any more. The reasoning is that ceramic pads don't outgas or dust up like semi-metallic or organic pads did, so the slots/holes aren't removing any gases or dust that prevent full contact with the disc surface.

If that was the case, then I would think with ceramic rotors, they would just serve to reduce the disc surface area and total braking capacity. Anybody have any definitive sources on this?

I have no definitive sources off hand, but from what I can tell, all of the above is pretty much correct -- except that I'm pretty sure ALL types of pads (at least for street applications) have solved the outgassing issue, not just ceramics. So, stopping distance probably won't be improved by slots or holes no matter what kind of pads you have.


Originally Posted By: J. A. Rizzo
I was just wondering if it would be worth replacing the vented, flat-surface rotors on my SUV with drilled or slotted rotors to get a little better braking performance while towing a trailer. But then I was told that my Honda Pilot has ceramic pads, so I shouldn't do that.

AFAIK, for street applications:

- The main advantage to holes is reduced weight. Probably not going to make much of a difference for you.
- The main advantage to slots is to catch road gunk and prevent it from scoring the rotors. Might be worth considering.


However, slots and holes both might increase pad wear, and good slotted and/or drilled rotors cost a lot more than blanks.


If you want more stopping power, try to find bigger rotors and a caliper relocation kit (provided it'll fit under your wheels). If heat-induced brake fade is an issue, try to find 2-piece rotors. They cool better, are less likely to warp, and keep the heat away from your wheel hubs. Higher performance brake pads can do the same as either (or both) of the above, at the cost of more dust, more noise, worse cold performance, shorter life, higher rotor wear, or any combination thereof.
 
If you are having braking issues on a stock well maintained braking system on a modern car, you are either driving like a teenage boy who just got his license or inattentive to road and traffic conditions.
 
Thank you everyone for the replies. I really appreciate all of your insights. You're basically confirming what I'd heard, and it makes logical sense to me that the ceramic pads would not have the same problems as the pads did when drilled and slotted rotors first came around. I'll stick to turning the existing rotors and replacing them when they're out of spec, and setting the trailer brakes properly, and anticipate the stops.

Never heard of cryogenically treated rotors before, but I guess it's not completely ridiculous. After all, I used to buy cryogenically-treated guitar strings... :)

http://www.guitarnotes.com/notes/noteget.cgi?cryogenic_strings

John
 
There may be something to cryogenically treated rotors, but I wouldn't worry about it unless you are having serious heat issues.
 
Originally Posted By: scurvy
Originally Posted By: BuickGN
There are many that still make quality drilled rotors. You guys are making blanket statements here regarding reliability and pad wear. In some cases it's try, in others it's not. I have $2,000 in front brakes, it's not some cheap kit that's going to come apart on me. I don't recommend the $100 drilled rotors.


While I don't disagree with your statement that "There are many that still make quality drilled rotors" it certainly leaves room for my statement that there's a lot of junk out there for those of us that won't spend two large on front brakes alone. I certainly wouldn't spend that much on brakes, but my cars are daily drivers & family haulers, not weekend track cars.

So I wholeheartedly agree I'm making a blanket statement - for the kind of brakes 99.9% of people will be buying.


I agree with you that there's plenty of junk. I have to wonder about these $100 crossdrilled rotors. The holes HAVE to be an afterthought. It's scary to think that there are probably companies out there drilling rotors that were never meant to be drilled.

I got carried away with the brakes but the stock 5at brakes on the TL leave a lot to be desired. I've never lost them completely due to fade but with even a little heat in them you would think they're warped and they are warped sort of. Once they cooled the felt fine. I got so sick of this I didn't want to replace them with stock rotors and one thing led to another and here I am with overpriced brakes.
 
Originally Posted By: artificialist
Why do S-Class Benz cars leave the factory with drilled discs?


Maybe Mercedes engineers discovered excessive pad gassing during panic stops from 140 MPH.

On 99% of road cars, it's silly to have slotted/drilled rotors. Track cars are another matter.
 
Originally Posted By: artificialist
Why do S-Class Benz cars leave the factory with drilled discs?



same reason they leave the factory with a 3 pointed star ornament on the hood and pretty shiny alloy wheels......looks designed to capture a potential buyers eye.
 
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