Explain brakes to me: standard vs. drilled, slotted, sequined, etc.?

2003 Z4 3.0i auto

I feel a pulse in the rotors and I knew they were getting ready to need to be replaced, according to the dealer. I'm going to do pads and rotors all around. I probably won't take it to the track again any time soon, if at all, before selling it. The price isn't much different between normal and drilled/slotted. Are they worth getting for a DD that gets ridden pretty hard but not raced?

A guy at the track with a Z3 said that drilled/slotted aren't good for DD because they don't give enough mass to sink heat before getting too hot, but wouldn't racing be the ultimate place where you would need to handle heat...? Didn't make sense to me so that's why I'm asking, for this car in particular and for cars in general

Thank you, oh great hive mind.

Well, if you had a 3.0si, I’d send you my almost used up track pads, and 4 to 5 cold brake applications would likely clear your problem right up— and turn your wheels black!  You problem is most likely pad deposits on the rotors.

Actually, the rears would likely fit your vehicle, but not the fronts. 

Oh— and I’d skip drilled/slotted. Go with Centric rotors from RockAuto

Call GRM, get June 2008 issue, read it, know it, live it.

short answer:  for a street car, drilling rotors is a waste of machine time.  Slotting is marginally less wasteful.

Ive always used plain blanks for my street cars. Never had issues. In fact I just bought some from rockauto tonight.

I tried slotted ones once on my IT car.  They cracked in the bottom of the slots.

I've had really good luck with slotted rotors over the years.  I think any benefits over blanks are marginal though.  I have a wprking theory that the slots should help with evacuating gasses from hot pads.  Surprisingly I have never had wear issues with them but I typicall make sure it was a good quality rotor like centric or brembo to start with.

Plain blanks on every track car I've had (Audi, BMWs). Never warped a rotor though they will eventually crack after a lot of use. I like throw-away pricing on parts like this. I'd rather spend money on really effective brake pads.

Thanks guys. Standard it is.

I should have sold the car one week ago though. Yesterday I stopped along the highway to help someone and ran over a big screw. I figured I'd take it to the Honda dealer, I got a coupon in the mail for an oil change anyway, and its gotta be less there than BMW right? Well when they order in the correct oil it's $125, might as well go to BMW and get the hand wash too. Also they say the screw is too close to the sidewall to patch and I'm not sure I can trust a plug for "spirited" driving. 50% tread left. 

And of course the brakes. BAH!

Be aware that many times drilled/slotted rotors can't be turned/machined.  Not that machining rotors is a common thing any more, but something to think about.

Depending on the chamfer around the holes, drilled/slotted rotors can add noise.

On a DD, there really is no need.  Pulsing rotors can come from warping or inclusions.  Warping is self-explanatory.  Inclusions happen when you have really hot brakes and come to a complete stop.  The hot rotors burn some of the pad material into the rotor like a hot iron skillet burns a pancake.  In the case of the skillet, it ends up being a good thing as it fills the pores with carbon.  In the case of the rotor it ends up making uneven friction surfaces.  One of the ways to combat this is to get rotors with the most possible mass and strength to distribute a greater amount of heat energy. Drilled/slotted rotors don't do that.  They're also only a benefit if you have significant outgassing during high-performance driving situations which a DD won't likely see.  

With the cheap prices on most rotors these days, I suggest getting regular rotors and just replacing them when they start getting wobbly.  Do a proper bedding ceremony on the pads.  I like to do 60-5, 50-5, 40-5 mph braking at threshold for a few times to get them good and hot, then drive around for 15 minutes or so without using them so they cool off.  During bedding, make sure to not come to a complete stop with the brakes or you'll get the pancake on the skillet.  Stop most of the way with brakes, then pop it into neutral or use the hand brake if you have to stop.

The theory here is that (depending on the pad material) is that you force it to do a process that it would do over time anyway; convert some of the surface pad material into crunchy burned bits.  Soft, unheated pad material might otherwise become burned into the rotor's pores instead of staying on the pad.  To continue the analogy.... putting fresh pancake batter in the skillet, it will stick when you try to flip it.  If you put an already cooked pancake in the skillet, it doesn't stick.

I wouldn't consider anything but plain rotors for a car that doesn't see track time. For a track-driven car, maaaybe slotted, possibly scalloped, drilled is asking for trouble.

BTW, AngryCorvair is an engineer for braking systems, so I'd say his words (and articles) carry some weight.

Slotting is used to reduce pad face glazing, something that can happen to street cars (my wife's for example) and I'm sure there are other benefits as well.  The rotors can be ground on a mill (like a flywheel), but they cannot be turned on a lathe.  Most cars have rotors that are inexpensive enough to replace rather than face them.

Drilling reduces weight somewhat, but was originally used to reduce the gasses from old style pads from building up between the pads and the rotor causing reduced braking effectiveness.  Similar to how cold, wet brakes can be difficult to use until the water is removed and the system is warmed back up again.  Newer pads don't have this gassing issue, but for many it is still done for appearance.  Some manufacturers use them (Porsche, Ferrari, etc.) to help manage the thermal mass of the system in order to keep the oversized rotors and multi-piston calipers within their working range for the street.  Quite a lot of decisions for these cars were driven by what they can do from the factory to allow racers to use them in various classes.  Porsche especially.  So if you aren't allowed to upsize rotors and calipers in your class, buy the factory car with them already installed.  Toss the drilled rotors, use blanks/slotted, etc. and get to racing.  This isn't as big a deal as it used to be as racing series seem to be a bit more open to braking options and the general growth in wheel sizes allows a greater range of rotor options.

Note: the above is thrown out the window for Ceramic/Carbon Fiber, etc. as those are quite a bit different in how they work with regards to thermal mass, etc.  The basic mechanics are the same though.

The biggest importance for a good braking system is:  Bedding the pads properly, this reduces the chances of "warping" by evenly distributing pad material onto the rotor faces.  There are procedures online to follow.  The rest of it is making sure you use good quality components and that they are in good working order.  This means, calipers and pads that slide easily.  Fresh, clean fluid at the calipers.  No leaks.  Flex lines that aren't soft and bulging, etc.

This engineer explains it pretty well.

https://youtu.be/78wbht355R8 

so probably a dumb question but why cant a drilled/slotted rotor be turned on a lathe? Back when i was 17 and bought a $500 240sx and i wanted to be cool and get drilled and slotted rotors, so i bought the cheapest set off of ebay, when i got them the directions suggested turning them before installing (i guess cheap ebay rotors warp themselves before even being put on), i was in an automotive vo-tech class at the time so i used the brake lathe and turned all 4 of them down without an issue.

Maybe I’m going something wrong, but I’ve never had good luck with slotted rotors on the track. No matter how hard I try to follow proper bedding-in procedures, I always ALWAYS end up with uneven pad transfer and massive vibration. 

I’m back to plain rotors. I get more bang for my braking dollar with high-end racing pads and the best tires I can afford.

In reply to LanEvo :

What brand of rotor?  The 300Z I rent a seat in for Champcar uses Autozone/NAPA/whateversonsale slotted rotors, and sometimes the vibration is BAD.  The 350Z I run in WRL uses Brembo slotted, and is smooth as silk.

I do have drilled rotors on the back of my explorer, but thats only because they were on blow out from amazon. $17 from $110 with ceramic pads and rotors was hard to pass up. Theyve worked for years now, they seem better than what i had before.....which wasnt great really