Jesse Asis

For those that are interested in upgrading from a stock rotor to either drilled or slotted, read this from an engineer's stand point. I helped me make my decision to just get drilled rotors on all four corners. Thank..

There are many claims as to the benefits of drilled vs slotted rotors on stopping power. This guide is intended to provide some facts about drilled and slotted rotors. As a member of the SAE (Society of Automotive Engineers), I was pleased to see a paper "The Effect of Rotor Crossdrilling on Brake Performance" by two GM engineers published in 2006. They examined three vehicle platforms with cross-drilled rotors vs standard rotors to measure convection cooling capability, fade characteristics, wet braking, pedal feel and lining wear. The result is summarized as follows:

For the sports sedan, the coefficient of friction was 21% higher for drilled rotors than standard front rotors at 340F and higher using 15 brake snubs at 62mph. The track simulated 124 mph fade test showed 37% better brake output for drilled rotors. The drilled rotor brake temperature was about 150 degrees cooler.
For the performance car, the coefficient of friction was significantly higher for drilled rotors especially at high temperature.
Wet braking at high pedal pressure was the same for drilled or standard rotors. Wet braking is not significantly improved by drilled rotors.
Pedal force was much more consistent with drilled rotors over the brake temperature range. That is, to stop at the same deceleration rate, the driver does not need to modulate pedal pressure based on different brake temperatures. This reduces driver fatigue and improves brake response.
The authors also reported that drilled rotors prevent pad resin glazing on the rotor. So we now have solid evidence that drilled rotors have benefits over standard rotors. However, I have not found any published paper to show how slots affect brake output. So I reviewed inertial dynamometer tests using ISO NWI 26867 from Link Testing in Detroit with slotted rotors vs standard rotors. The results showed no significant difference in the coefficient of friction during the fade sections, hot stop section or pedal sensitivity portion of the test. My hypothesis is that slotted rotors do not contribute to rotor cooling whereas drilled rotors improve convection heat transfer to cool rotors and reduce brake fade. I should also point out that the pad lining wear for the slotted rotor was very severe during the test, i.e. the pad was chewed up over 20% more than the lining with stock rotors. While I believe that slots will help remove gas and debri from under the pad, I am not sure that this has a significant effect on brake torque for normal street driving. Perhaps the effect of slotted rotors is more significant on the race track, and conversely, I believe that drilled rotors are better for street and highway driving. For most drivers, I recommend drilled rotors over slotted rotors, and this conclusion is supported by the fact that Corvette, Ford GT, Porsche, Mercedes and BMW come with OEM drilled rotors.

Eric D

Jesse,

If you are sharing your findings on the forum most people here on the forum appreciate it. That’s a good thing. However, most of us while in school learned that doing a book report, we also had to include a bibliography. It would be helpful if you had included names, SAE document number and other sources of your gathered information.

BTW, drilled rotors may perform better for a period of time, but a lot of folks have found they will crack much sooner than solid from track use. You can find threads here in the forum documenting this. Part of the reason you no longer find them on new Corvettes.



ps, you should really take sometime to fill out your profile so we have some idea of what type and year vette you are driving.

AU N EGL

How is the coefficient of friction of a HOLE greater then solid sides ?

BUT what they did not say or show is REAL APPLICATIONS.
here are a few pics from minimal use on tracks









and less the one hour use. TWO twenty min session


and ONE twenty min session



Yup those drilled, milled or cast in holes work great.

Drill and slotted rotors are 40 year old technology to release or out gas asbestos brake pad gasses. Guess what? asbestos has not been used for brake pads in 40 years, so no need for holes.

Why do manufactures keep putting holes in rotors? because the customer wants them. PERIOD. No functional use.

That research was flawed.

vettenuts

When did they get rid of them? I thought I had seen them on the Z06 and ZR-1 but then again I haven't looked at a brand new Vette in a couple of years.

Eric D

As far as I know (I could be wrong) but the last performance vehicle with them was the 2009 CTSv. the new ones have solid. The ZR1 is different in that they are carbon ceramic, but yes, they do have the holes.

Evil-Twin

I dont see no stinkin cracks... of course my car is a street car and does not see any real stress but then my holes have a sinuous curve which takes away any hot spots or stress in the corners, because there are no corners... No, I'm not going to show my drilled and slotted rotors, which have 70,000 miles on them, and they are 8 years old...again...
I believe I have reached my limit on the number of times I have embedded them in a post... Its not s garage queen either.. Lots of 200,000 dollar cars use drilled rotors..Of course I think they are sexy.. Ive had five different ppl PM me this morning and last night that they are going to try to attempt to make their rotors look like mine..I get this every spring..a dozen or so see a couple of old threads and they get hungry for the knowledge..Drilled and slotted rotors do not belong on the track..just like ceramic compound pads do not belong on a street car..

AU N EGL

That is because the customers want them, not performance braking. also on the Z51 rotors.

The Brembo Carbon ceramic are on rotors for the ZR1. Very different brake set up. Not better IMO, but different. Keep the wt down.

AJ Powers

Why not? I was about to get the Hawk ceramics for my street car

hotwheels57

Ceramics don't dust which is why people like them. But they also don't have the same friction/stopping characteristics as oem or similar.

vettenuts

I honestly couldn't tell the difference, either in braking or dust. Of course, in comparison to my wife's BMW the Vette makes not dust whatsoever

Pumba

Perhaps the research is not flawed.

I have track and street time with solid rotors and with rotors with holes in them.

This first picture is of my StopForce front rotors. Many forum members are aware that StopForce built their rotor assemblies by purchasing Porsche rotor assemblies, throwing away the Porsche hat assemble, and installing an aluminum hat assembly that they had machined specifically to fit a C5. In over two dozen track days, with Hawk DPS 70 pads, no cracks:





This second picture is of my Baer Eradispeed +2 rear rotors. This is the third set of these rotors I have had on my Z. The first two sets developed cracks in about two track sessions each using Hawk DTC 60 pads. Once the cracks became large enough to feel through the pedal while driving on the street, I replaced the rotor set.






I believe the reason that the Porsche-based front rotors haven't cracked is because Porsche doesn't drill the holes in their rotors. They cast the holes in. Hence, no sharp edges that create stress-risers.



So, rotors with holes can be fine, if they are manufactured properly.

tommie

great information!!!!!

i never knew about the porsche/stopforce rotors..

I have just been using GM blank rotors (not drilled or slotted)

alxltd1

So, would the dimpled drilled rotors from Brake Performance mitigate the potential to crack as they are not drilled fully through? I have no idea of the technology used in drilling/dimpling or if it would lessen cracks because of heat and stress or if the dimpling presents no corners for cracks to start, but wondering if anyone has any experience with them. I am not looking for a track rotor, only a street replacement, and yes part of the reason is the "look" (but dont want to give up function or longevity to get it).

TEXHAWK0

I still stick with my opinion that drilled or slotted rotors are just for show on a street car, and can cause rotor failure on a track car.
How many race cars do you see with drilled rotors?
At one time, there may have been some benefit to control pad gassing, but that is minimal with modern pads.

I do think that the slots and holes will increase brake pad wear by adding edges, but they actually reduce the braking surface.

That's my story, and I am sticking to it...

TEXHAWK0

What advantage could adding dimples produce?
Anytime you have an extra edge, there is potentially higher stresses there.

JR-CRUZN-C5

Well boys show me a Drag Racing car in a Pro-Class that DOES NOT have drilled and slotted rotors!!

JR

AU N EGL

IIRC Porsche uses ZIMMERMANN rotors and just ask P-car mechanics how often they change those Zimmermann rotors. Thicker rotors do last longer. an do not believe they holes are cast in but all drilled. and camfered edges make no difference.

and by the way, the last photo above, is a Zimmerman rotor. did not last 20 min

for street use, mild spirited driving, not a problem with D/S rotors.

ctusser

Stopping once an hour is a lot different than stopping every 10 - 30 seconds.

wheelhorse

Another post about Drilled, vs. Drilled/Slotted, vs. Plain Flat surfaces rotors without any definitive outcome. Track, street, looks good. Bottom line, when it's time to stop just through the anchor out the window.

Dave68

The latest Cadillac CTS-V comes with slotted rotors, as does the Viper ACR (track-specific) car (which set the "Ring" record in Germany).

Even the incredible Caparo supercar has slotted-only rotors.

Apparently, none of the designers and engineers working on those cars has a clue!