Brake Discs: Drilled, Slotted, Both, or Neither?

[GRiDRaceTech]

I love stopping. It's fun, and it prevents nasty crashes. However, some people seem to have some misconceptions when it comes to performance braking. I'm going to describe each form of disc design and its upsides and downsides.

Blank
Blank brake discs have no dimpling, slotting, or drilling. They are just a clean, smooth face. The advantages to blank brake discs are that they have the most surface area, are very easy on pads, are the cheapest, and resist cracking very well. The disadvantage is that they don't have areas to expel gases. However, that disadvantage is pretty much a moot point considering most modern pads don't build up gases enough to create a skating effect. However, most of the time blank rotors are not available with directional vanes, which is sometimes a very big buying point.

Drilled
Drilled brake discs are essentially blank brake discs which have had holes drilled or cast into them. The cast holes will resist cracking more than simply drilling holes, but if the drilled holes are chamfered correctly no problems should be had. Also, buying a drilled rotor which has been cryo-treated is a good idea. The idea behind drilled rotors was to create areas for the gas which built up between pads to be expelled. Another bonus is a lighter overall disc, thus lighter rotating mass and less unsprung weight. The least important bonus is that they look blingin'. However, the disadvantages are: decreased cracking resistance, increased pad wear, decreased brake disc surface area, and higher replacement cost.

Slotted
Slotted brake discs are blank brake discs into which grooves have been cut. The grooves may extend in an arc to the outer edge of the rotor, or in straight lines. Advantages: less prone to cracking than drilled, usually cheaper than drilled, often have more surface area than drilled, lighter disc, blingin'. Disadvantages: increased pad wear, decreased surface area compared to blank. Often available with directional vanes.

Slotted and Dimpled
I can't see a point other than some people may consider them more blingin'. Buy 'em if you want, but don't pretend the dimples actually do anything.

Drilled and Slotted
Combines both drilling and slotting in one disc. Too much loss of surface area makes these bling-only. Almost every professional race team in the ALMS runs either drilled or slotted brakes. (Mostly SLOTTED[stupid me]) I'm fairly sure the combination was created for looks, not track-worthiness.


In the end, slotted wins. Slotted rotors will simply be the best for any street-based car. Coupled with good composite pads, they will offer the best fade resistance for lasting pedal feel and worry-free stopping.

If anyone wants to chime in with data or knowledge feel free.

[Emagdnim]

How about the differences in the material of rotors. Alot of people think steel rotors are best and they would be wrong. While steel has a higher tensile strength, cast iron is many times stronger than disc brake requirements. Its thermal transfer characteristics are significantly better than those of steel so that the heat generated at the interface between pad and disc is efficiently carried through the friction faces to the interior surface of the disc and into the vanes from where the heat is dissipated into the air stream. Cast iron is more dimensionally stable at elevated temperature than steel and is a better heat sink.

I do beleive there are other more exotic materials being used for brake rotors(titanium) but I think cast iron is more then enough for any road car.

[jboss]

what makes your car stop faster----short answer--better tires

read the definitive article http://www.wilwood.org/pulpfriction.pdf

or here
http://scirocco.dyndns.org/faq/brake...n/pfpage1.html

[Tsunami]

Now the trend is toward slotted rotors. There have been some issues with the cross-drilled rotors. Although they look cool they can sometimes be prone to cracking in between the holes. The slotted rotors don't have this problem, and they still serve to ventilate the rotors just like cross-drilled ones. I would go with the slotted rotors.

As for stopping tires will provide an increase in grip, but upgrading to better rotors will increase your stopping power as well.

[jboss]

Actually, stopping distance is what we are really worried about not braking power ( you called this stopping power which confuses the issue).

Bigger brakes, slotted brakes, drilled brakes etc WILL NOT reduce stopping distances unless your stock braking system is incapable of locking the tires---unlikely on most modern vehicles.

While big brake kits, fancy rotors and pads may change the FEEL of your brakes, improve or ruin the ability to modulate the brakes etc etc... they can not improve stopping distances because the limiting factor is the grip of the tire and not the ability of the brake.

These "upgrades" are rarely necessary even for racing and track events unless the brakes are unable to keep up with the amount of heat produced by your braking---highly unlikely in a drift car where the sessions are short and speeds are relatively low.

IF you are having issues with brake fade the things to do first are always 1) use an appropriate pad for your heat range and 2) use an appropriate fluid for your heat range. IF you are still having problems with heat, add brake cooling ducts......and as a LAST RESORT install larger brakes.

Notice that I never mentioned using slotted or drilled rotors because they are simply a waste of money unless you want to look cool or save a few grams on unsprung mass. Both were designed to help with "out-gassing" when the brake pads get so hot that they vaporize on the surface forcing the pad to float on a cushion of gas instead of touching the rotor----this is exteremely rare with modern performance race pads as they must be extremely hot (hotter than your brakes will get without boiling even the best fluid first) to do this.

So.....how do you know what you need to do for brakes???

First, have you ever had a brake fade or failure at an event?
If not, you probably need to do nothing.
If so, first check to make sure your STOCK system is in good shape and use a fluid and pad that are in the appropriate heat range.....

If you still have problems.....

1) You have to push the brakes harder and harder during a session in order for them to work---pedal may feel hard.
---Either your pad is outgassing as explained above, or your vacum operated brake booster is running out of vacum because you are at or near full throttle a lot.
---solution---replace pad with higher temp range pad...disconnect the vacume line to the brake booster and deal with the harder pedal or add an additional vacum resevoir to the system.

2) Your brake pedal becomes mushy or you have to pump the brakes to make them work----this is caused by over heating and boiling the fluid in the calipers.
----solution replace fluid with NEW---CLEAN higher temp fluid..

[Emagdnim]

I agree if you can lock the tires with the brakes then the only way to decrese stopping distance is more traction(grippier or wider tires) and/or better balance between the front and rear brakes.

The only reason to go to a larger more powerful brake system is if your current brakes aren't enough for your current available traction.

[LucidStrife]

drilling bad

I would definatly say that drilling your rotors would be a bad idea. If the weight of the rotors is such a big deal then I would focus on slotting it, getting a lighter material to have your rotor made out of, or maybe a smaller rotor is in order. Drilling hurts the rotor life by quite a bit, and hurts the cooling efficency of the vented rotors. I have heard that the life of a drilled rotor can be shortened by 80%, and the weight your losing is important, but not that important. I just cant afford to have my rotors changed out that often.

Lucidstrife

[Tuner]

Another vote for slotted

[ma71supraturbo]

Originally posted by jboss
Bigger brakes, slotted brakes, drilled brakes etc WILL NOT reduce stopping distances unless your stock braking system is incapable of locking the tires---unlikely on most modern vehicles.

Negative ghostrider. Tires have the most "grip" at around 10% slippage. You want a brake powerful enough to be able to HOLD the brakes just before lock-up for a long period of time. Hell anyone with a 1950's chevy can lock up all four tires at come to a sliding stop, but it certainly isnt the shortest or safest way to do so.

Bigger brakes increase the torque applied (larger rotor has more leverage than smaller) and also increase the surface area to help keep fade at bay.

Drilled and or slotted rotors increase the disc surface area and therefore help to transfer more heat to the atmosphere. However their effect is minimal in comparison to a bigger brake disc. Unfortunately bigger brakes require bigger wheels and the whole package weighs more -- so there is a certain point where you experience diminishing returns...


Modulation is helped mostly by having braided brake lines, quality fluid, and pads capable of withstanding the temperature range you anticipate. Additionally brake bias plays a large part as ideally you have all four tires starting to lock up at once (street cars almost always have the front tires lock up first to keep people from oversteering). The result is a slight loss in braking power.


Perhaps the most overlooked "brake" upgrade is installing stiffer springs. Soft factory springs will promote brake dive -- where the nose squats under hard braking. A lot of weight is transfered up front and the front brakes are overloaded with most of the work. Additionally the nose dive will cause suspension to add more negative camber so your tire's contact patch lessens (meaning your tire's have less overall grip)

[SaintDrift]

Wow, I know when I'm performance driving, I always brake in a straightline. Limited nose dive is good, it keeps weight where you need it in a turn, towards the front. Once again, negative camber increases the contact patch in a turn. If you want to be fast, you trailbrake.

I don't know about you, but I've never had a car fade from the rotors overheating. Usually it's the brake fluid. So increasing pad to rotor surface area is good. Drilled, slotted, it's all bling. Go out and get you some good pad, steel brake lines, then some good brake fluid and call it a day.

[Ripper]

Originally posted by jboss
what makes your car stop faster----short answer--better tires

read the definitive article http://www.wilwood.org/pulpfriction.pdf

or here
http://scirocco.dyndns.org/faq/brake...n/pfpage1.html

actually, it's all dependent variables for less stopping distances. depends on disc size, caliper size (surface area), and how much pressure is applied on the brakes.
personally i'd choose crossdrilled/slotted break rotors becuase they have the "sporty" look and it cools down the brake disc.

[hatebbobbarker]

has anyone seen rhys millens brake setup?
its wild.

[GRiDRaceTech]

Originally posted by SaintDrift
Wow, I know when I'm performance driving, I always brake in a straightline. Limited nose dive is good, it keeps weight where you need it in a turn, towards the front. Once again, negative camber increases the contact patch in a turn. If you want to be fast, you trailbrake.

I don't know about you, but I've never had a car fade from the rotors overheating. Usually it's the brake fluid. So increasing pad to rotor surface area is good. Drilled, slotted, it's all bling. Go out and get you some good pad, steel brake lines, then some good brake fluid and call it a day.

Dive is never good, it decreases rear grip and increases the propensity of the car to oversteer.

Negative camber CAN increase the contact patch in a turn, but only to a certain extent. A MacPherson strut will undergo positive camber change under load, yes, but only to a certain extent. Thus, too much negative camber and you have a decreased contact patch. I have a feeling you already knew this from your other posts (you sound very well versed in high-performance driving) but I just wanted to reiterate it to the newbies.

I agree that fade is usually brake fluid related or both brake fluid and pad related. I have good pads and great brake fluid and my brakes are awesome. I need to upgrade to stainless lines next for good feel.

[Craftsman]

Can I vote?

I vote for combination of sloted and drilled...

The reasoning behind my choice... Slots mainly are good for warming up the brake pads. They do an excellent job of warming them up. The drilled ones help in braking... So I like using both... Only problem is that the chances of wear occuring faster is only increased...

Matt.

[driftfreak]

before you vote...read this arcive of a discution on this very subject
http://corner-carvers.com/altimathread.php.html
very interesting read,,,but very long...