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Brake Rotors: slotted versus drilled

68.169.27.47

Posted on August 20, 2004 at 21:09:12
Posts: 1187
Joined: April 5, 2000
Ahh, off the General forum and onto a more proper venue:

After MUCH research and chatting with various engineers (including a main tech from Brembo, a guy from the Prodrive race team, and others)...

Here are the basics:

We are talking about relatively lightweight floating rotors with aluminum caps (think Brembo GT series, though this still applies to Tarox and the like). We are also (generally) discussing more race/inspired driving versus a 'grocery getter.' Lastly, your driving style (or lack thereof) and brake pads can make a HUGE difference as to how much heat and grip your brakes may generate. Lastly, naturally you would want to use proper race brake fluid (Motul 600 or the like) due to a higher boiling point (to avoid 'cooking' the brakes... also called brake fade).

Like in audio, a single components does not work alone, it is within A SYSTEM and as such, one needs to account for both front and rear systems on a car. Think Brembo GT series brake rotors, though this still applies to Tarox and the like.

DRILLED: Has LESS metal material and therefor has less metal to dissipate heat. Also, drilled can play 'connect the dots' (read: crack). Will avoid discussing rotor warping.

Keep in mind many companies just drill holes in a solid rotor and the holes ARE NOT part of the manufacturing process. This can cause metal irregularities and 'connect the dots.' Yes, the holes may help during rain to rid water float, yet the same can be said for slotted (and slotted is more effective here due to the wiping effect of the angled slots). And if you feel drilling saves weight on the rotors, it does, but it also LOWERS the amount of metal on the rotor that stops the car. As i recall, solid rotor is 100% material touching the pad, slotted is about 92% and drilled is 85%. More metal equals more pad grip and lower stopping distances.

SLOTTED: More material than drilled means better heat dissipation. During wet driving the slots have a better wiping away of water versus drilled. Slots also wipe the pads to keep the pad surface clean.

Am avoiding the whole brake pad out gassing issue as this MIGHT happen DURING bedding in, yet once the pads are bedded this is really a nearly moot point on modern high-performance pads.

If you are just Joe Driver with the sporty Grocery Getter, a stock setup is fine. If you enjoy more inspired driving in the streets, aftermarket slotted can help but MAKE SURE you match the front and rear as there is a balance (front/rear bias) engineered into your car's brake system and if you do not know what you are doing, altering this balance can spell disaster.


Lastly we have those who track their car or do AutoX. Will attempt to keep this short and sweet. Here is where one may choose to add bigger rotors and better clamping (more pistons) brake system. With rotors, size in not **everything** as you might also be adding unsprung rotational weight (bad). This is why top quality larger rotors usually have LIGHTER WEIGHT aluminum center hubs since it is a 'known good' alternative at saving weight over solid rotors. Am avoiding discussing calculating rotational mass and how it alters the vehicle performance.

As for brake balancing (front/rear biasing) for track, you can either play around with different brake pad compounds and/or have installed a brake bias adjuster. Why have adjustable bias (front/rear balance) of the braking system? Because different tracks and track conditions can be fine-tuned for optimum lap times. As an example, during wet track days you will want to increase the percentage of rear brake biasing a bit.

Brake fade, using the brake system to the point where overheating cause a less effective (or totally vanish) performance can be dealt with through proper cooling. As mentioned earlier, solid is best due to more metal while slotted is second best (with drilled being last). During track events one would measure the heat on the system and choose the right fluid and pads so that their heat rating is within set parameters. If the system is achieving too high a heat, brake cooling ducts can greatly help lower temps to a certain degree. If the brake system is below said parameters, one may choose different pads rated accordingly.


GET REAL:

Frankly, in the end slotted or drilled brake rotors is not needed for the average American driving their car on the street. Speed limit laws in most countries assures you never get anywhere near the edge of stock brake system performance for stopping power or brake fade, wet or dry conditions. It is only those who truly use their systems for AutoX, track days or the like that will want to carefully consider a properly engineer SYSTEM for their given vehicle, driving style, and track conditions.


BLING FACTOR ONLY: Get wherever (sane system) you want to look cool and brag to others, but PLEASE make sure you have the front/rear brake bias correct. Incorrect biasing can KILL you and/or others.


NOTE: there is A LOT of misinformation on the Internet concerning slotted or drilled rotors by inexperiences, uneducated, or skewed marketing people (just as inexperienced/uneducated/marketing people may provide reviews of audio gear). PLEASE talk to TRUE professional engineers who have vast knowledge and experience. BE HONEST WITH HOW YOUR BRAKE SYSTEM WILL BE USED!!! Also, one may choose great rotors and calipers, yet use basic pads/fluids for the street and change pads/fluids for track days.


Please avoid the BLING factor as your brake system is a balance and altering this can cause DEATH! THE LIFE YOU SAVE MAY BE YOUR OWN.

Enjoy the Music,

Steven R. Rochlin

 

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follow up, posted on August 21, 2004 at 07:23:45
Ed Sawyer
Audiophile

Posts: 2593
Joined: November 3, 2000
"As for brake balancing (front/rear biasing) for track, you can either play around with different brake pad compounds and/or have installed a brake bias adjuster. Why have adjustable
bias (front/rear balance) of the braking system? Because different tracks and track conditions can be fine-tuned for optimum lap times. As an example, during wet track days you will
want to increase the percentage of rear brake biasing a bit."


Well, playing with biasing is generally not a good idea, even for experienced racers. It's all too easy to overbias the rears, which will quickly lead to a spin. The front does 60-80% of the work in most cars, (except maybe those with more rear weight bias, e.g. 911, NSX, etc.) and adding more rear bias isn't necessarily going to help in general. In an iffy situation, it will/may result in rear lockup sooner, which you never want. It's also too easy to mis-adjust it on the fly, I know people who have spun/crashed/gone off because of this, and they were fairly high-level racers that knew what they were doing, just happened to hit the lever or knob at the wrong time.

Anyway, good info in the above post! (time to Track your car soon, methinks. ;-)

-Ed

 

Re: follow up, posted on August 21, 2004 at 08:10:43
Posts: 1187
Joined: April 5, 2000
Ed,

Cool! Thanks for chiming in! Always good to meet a racer :)


>>>Well, playing with biasing is generally not a good idea, even for experienced racers. It's all too easy to overbias the rears, which will quickly lead to a spin.<<<


Agreed, and one needs to be VERY cautious with brake biasing. This is why i was very, VERY, did i mention being VERY adamant about keeping stock brake bias for 'normal' drivers. As you know there are professional bias adjusters that allow for SMALL increments of adjustment. This was part of the reason i am soooo glad to have connected up with the Brembo guy as he was THE ENGINEER AND TESTER who designed the system for the Ferrari and, as such, was able to give me top quality advice/tips/pad choices, etc.


>>>The front does 60-80% of the work in most cars, (except maybe those with more rear weight bias, e.g. 911, NSX, etc.) and adding more rear bias isn't necessarily going to help in general. In an iffy situation, it will/may result in rear lockup sooner, which you never want. It's also too easy to mis-adjust it on the fly, I know people who have spun/crashed/gone off because of this, and they were fairly high-level racers that knew what they were doing, just happened to hit the lever or knob at the wrong time.<<<

Agreed. One needs to be VERY cautious about biasing. Locking up the rear first is a fast way to crash... or die :(


>>>Anyway, good info in the above post! (time to Track your car soon, methinks. ;-) <<<

2005 baby. Was hoping for late in the season 2004, yet am still tuning her. Kinesis is a bit late at delivering my new lightweight special rims as the Ferrari has a specialized offset. Between the new rims/tires/brakes this should lighten unsprung mass by about 12 lbs per front corner and 8 lbs per corner rears. Will know more once i get all the bits and weigh in.


FYI: The rims will be 17x8 and 17x9 K27s. For the street will run the basic Mich Pilot PS2 (225/45/R17 and 255/40/R17) and am debating track tires. Once the rims arrive i will be checking tire temps and have the alignment adjusted for a middle ground as the car mainly will be street driving and about 25 or so track days in 2005. She has already been corner weighted when the new suspension was installed. Frankly, it is a compromised setup yet much better than stock IMHO. The new suspension system has really brought about positive results as compared to the lackluster stock Ferrari system. Been busy physically working out for endurance and strength while also reading many books to feed my head.

Could go on and on. So please share your wisdom, what car(s) you drive/race, etc. Always glad to meet a fellow racer and learn :) Tell us morw about you Ed :) :)

Enjoy the Drive,

Steven R. Rochlin

 

Re: follow up, posted on August 21, 2004 at 10:08:09
Rich Brkich
Dealer

Posts: 830
Location: Near Syracuse, New York
Joined: April 3, 2000
"The rims will be 17x8 and 17x9 K27s. For the street will run the basic Mich Pilot PS2 (225/45/R17 and 255/40/R17) and am debating track tires. Once the rims arrive i will be checking tire temps and have the alignment adjusted for a middle ground as the car mainly will be street driving and about 25 or so track days in 2005. She has already been corner weighted when the new suspension was installed. Frankly, it is a compromised setup yet much better than stock IMHO. "

Sounds ike its going to be a sweet set-up Steve. Have you driven around with the PS2s much? Plan on doing a wheel/tire upgrade for my GTI down the road and would be considerig the PS2s or the Goodyear Eagle F1s. I've driven a VW R32 with the Goodyear F1s and was very impressed with how the rode and handled.

Sounds like a fun ride!
Happy Listening,
Rich Brkich
Retailer & Audio Asylum Industry Liaison

 

Re: follow up, posted on August 21, 2004 at 10:20:29
Posts: 1187
Joined: April 5, 2000
Rich,

A most humbly thanks my friend. Alas, as the rims/tires are a 'package' i need to wait for the rims to arrive. FYI: Rims on her now are NOT stock, but Etoile 7x16 and 8x16. These will be used for winter (dare i say snow) driving and will get all weather rubber on them.

Have heard good things about the Goodyear Eagle F1s (and as you know there are various version of the Eagles and i assume you mean the GS-D3). Will report back on the PS2 in about 3 weeks or more as once they arrive i need to scrub them, measure temps across the tread, and possibly make alignment changes accordingly.

Enjoy the Drive,

Steven R. Rochlin

 

Re: follow up, posted on August 22, 2004 at 12:43:27
Rich Brkich
Dealer

Posts: 830
Location: Near Syracuse, New York
Joined: April 3, 2000

I might be able to forgive you for driving your beloved in the winter since you don't get snow on such a regular basis as we do up here in lake effect country. :-) ;-) My GTI spends most of the winter snuggled in my garage.
Happy Listening,
Rich Brkich
Retailer & Audio Asylum Industry Liaison

 

Re: follow up, posted on August 22, 2004 at 14:01:24
Posts: 1187
Joined: April 5, 2000
WOW, now that is snow :)

Ummmm... in the foothills of the Monadnock region we get snow my friend. We get snow by the MULTI-FOOT per eve!

Drive in the winter mainly to keep the fluids spinning and to get her all warm and happy.

Enjoy the Drive,

Steven R. Rochlin

 

...or, perhaps neither...., posted on August 23, 2004 at 19:41:58
Bill Leebens
Manufacturer

Posts: 3578
Location: Longmont, Colorado
Joined: April 4, 2000

Hey, Steve-----
St. Pete-based 'Vette Brakes does all the pieces for the factory Corvette racing programs, and adamantly insist aball-milled "dimpled" surface is superior to either slotting or drilling. They claim gas-venting is superior to either, and the rotors are far stronger, with weight comparable to drilled/slotted.

FWIW, YMMV...remember you promised heavy me a ride in the Ferrari!

Cheers, Bill.

 

Re: ...or, perhaps neither...., posted on August 24, 2004 at 06:29:54
Posts: 1187
Joined: April 5, 2000
Bill,

Stop on by for a drive this week. We are having GREAT weather! If you can wait until after September the new rims/tires/brakes and tweak alignment should be done. Going to Maranello in September to check out a few things :)

i kinda question the 'Vette out gassing part as modern brake pads really do not gas much like older pads, but hey, whatever works :) The new Vettes are truly impressive and must give them credit for FINALLY making it a truly competitve and great car.

Me? i love the classics... yet having an Enzo here would not be out of the question :)

 

excellent, posted on August 24, 2004 at 15:58:34
Replevin
Audiophile

Posts: 1206
Location: Washington, DC
Joined: January 21, 2001

Thanks for posting. I didn't even know we had a car forum! Here's a photo of my vintage 917 rotor.

 

Re: Brake Rotors: slotted versus drilled, posted on September 29, 2004 at 20:34:17
tvr2500m
Audiophile

Posts: 1672
Location: Boston
Joined: February 2, 2003
Fine post. There quite a few good starter books on this, like those by Fred Puhn and Carroll Smith.

The bling factor. Yeah. Bling. There's more of this bling-misengineering-thing going on that just with brakes. Huge wheels (revealing just how puny stock road car brakes are, exposing the rest of the bling effort as poseur), suspensions on bumps stops, wings... Not much of it is good "go" practice, and doesn't make good "show" either to those who know. And, yes, as Steven warns some of this bling could be dangerous.

- SJ

 

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