Alright everyone hears that you should automatically get them but I have heard from people that used them that they crack easily on the track. Is this true? Do they help enough to actually notice? I need new rotors and I always try to upgrade so just let me know if its worth it. Thanks alot.

 

i was wondering if the drill pattern matter on the rotors, hence the name cross drilled or slotted, i have seen many different patters also. I also was wondering if they are prone to cracking, and do they disperse heat faster than stock rotors?

 

up

 

http://fc3s-pro.com/TECH/MODS/BRAKES/rotors.htm




-Ted

 

Thanks mane.

 

Oh ya, is there anything you can do to the rotors to make them look decent? Like paint them or anything that will stay on actually? Will engine enamel work? I love the stuff because if you haven't used it it turns out nice without much work.

 

I have also heard by some pretty smart folks that unless the rotors are CAST with the holes, (instead of just taking a solid rotor and drilling holes in it), the rotor is weakened GREATLY and will likely crack due to the weakened state when heated......

 

Slotting, while it may help with degassing, reduces the surface area that the pads work with. I'd say the benefits are a wash.

However, slotted or drilled rotors are very expensive, not only the initial cost, but also because you can't machine them. 99% of all "warping" is due to the rotors being installed with too much runout. The rotor wobbles side to side. Braking is OK at first because the pads and caliper move around to follow the rotor, but after a while of driving, the high spots on each face (180deg apart from each other) get knocked down. This causes thickness variation and pulsation.

Here's the kicker... most of the time, runout is due to poor handling of the rotors before they're put on the car. You know how UPS treats boxes, right? If you want your rotors to last a long time you will trial fit them and use a dial indicator to check for runout, and have them machined as necessary. Remember, pulsation is not caused by being too thin, it's caused by thickness variation due to having too much runout. But you can't machine cross-drilled or slotted rotors! So once UPS or whoever gets your shiny new $150 rotors to your door, they're garbage.

The one shop where I worked, EVERY new rotor that went on a car was machined first. Zero percent pulsation-related comeback rate. I felt funny at first when I started at Saturn - we just slapped the new rotors on the car. Then I saw how the rotors are packaged - they come in enormous, sturdy boxes with a ton of protective paper/cardboard wrapping - no way they'll get jostled, jolted, or crushed.

All of this assumes the hub surface is completely clean of rust, of course.

 

lol.. why would you want to paint your brake rotors. im sure you could anodize them somehow.. what do they make rotors out of anyways? steel or spun alluminum?

scott

 

Wouldn't the paint just be burnt or scraped off as soon as you started braking anyway?

 

Well, the metal and thusly the anodization would wear out in no time flat. Honestly, just stick to painting your calipers and perhaps painting the hubs black.

I believe rotors are made out of iron...

 

Iron, some newer ones look/feel like they're made of powdered metal. Very bizarre metallurgy in effect - very light, yet huge (11x1.5") rotors. Aluminum rotors have been tried but you need special pads so the rotors don't MELT. Some circle track racers use really cool looking 3/8" thick titanium stop sign-shaped rotors...

 

first of all, crossed-drilled rotors can be machined(cut).i have had this done before on cross drilled/slotted combo rotors. it has to be done very slowly so that the hoes do not break the tip of the blade. instead of painting the rotors you can get a cadium plating that will prevent the rotors from rusting.also, if crossed-drilled rotors were so unrealible and weak why do porshe use them on some of their cars?

just my $0.02

 

I don't think I want to meet any of those hoes.

In my experience cross drilled rotors do stay cooler. I put rotors on a 4x4 I had every couple years due to warping, first set at less than 30k under warranty. Some of the problem was caused be oversized tires causing them to heat up faster. I finally broke down and put a set of cross drilled rotors on it and never had another problem.
I'm putting a set of cross drilled Bonez rotors on my rex this weekend.

 

I believe you're talking about the Metal Matrix Composite (MMC) rotors.&nbsp These have been around a while, bu they are costly and don't take much abuse before they warp like crazy.&nbsp Definitely not a track rotor!



-Ted

 

Cause Porsche is "old school" and still feel it looks cool...

Seriously, with modern brake pad compounds, there is no reason to be drilling the rotors...



-Ted

 

Porsche rotors are cast with the holes, so their is not a problem with stress cracks, but it is still more for looks.

 

I know I'm kinda a newbie in all this, but my buddies forum had the same discussion. From what I understand cross drilled cool faster because the air flow not only around, but through the rotors. As to the link and quote that they have less metal and less heat dispersion is wrong. When something heats, it expands. The the rapid cooling and shrinking that will cause cracking, but I doubt the rotors are cooling that fast. cheap rotors that aren't made correctly or made from cheap metals, that aren't homogenous may crack, but that's because they are cheap.
As for slotted, the reduced surface area is not a factor. Surface area has nothing to do with friction. Slotted DO help breaking because the pads make better contact with the rotors as the gas and brake dust are whipped away. Otherwise you are gripping the rotors with break dust, and that just doesn't work too well.
There are some cars (I believe Camaros, but I REALLY don't remember) that have problems where the rotors over heat and expand non-uniformly and warp, which, well, really ***** up the calipers, and then you really aren't stopping well. Were they drilled, teh cooling would have been slowed and the warping not as extreme.
But as I said, I'm a newbie, and that's my $0.02

 

Uh, that's BS...I'd like to know what "air flow" you're talking about.&nbsp If the rotors are typically vented, any airflow that's present will run from the center of the rotor backside through the fins and exit radially from the outside diameter.&nbsp With non-vented/solid disc rotors, you don't even have this type of airflow period.&nbsp Very few production cars have significant airflow brake vents that help cooling.

You're talking about my link?&nbsp I never said anything about "heat dispersion" - I mentioned heat retention.&nbsp Less metal, less heat retention - it's basic physics.

Uh, that's a stupid thing to say.&nbsp Friction ahs everything to do with contact surface and coefficient of friction.&nbsp This is all basic physics.&nbsp You're claiming totally the opposite?

Modern brake pads don't exhibit this trait.&nbsp Certainly no RACE brake pads either.&nbsp Do you see requirements for slotted rotors for race brake pads?&nbsp I sure don't.&nbsp I'd like to see opjective testing that a slotted brake rotor will out-brake a non-slotted brake rotor.&nbsp Certain top-tier race cars (i.e. F1) don't require slotted brake rotors for better performance; any slotted rotors that these race vehicles do use is to keep track of rotor wear.

Go pick-up some Race Car Engineering magazines - there's tons of info on cutting-edge (race) vehicle technology written up in there...



-Ted

 

Friction = coeffectient * Normal Force.

coeffecient of Friction does not depend on SA. Also, I believe rate of cooling is related to SA, which drilled has more of.

Also, I think i misread the heat retention quote.

 

ok, then so why the hell would anyone buy slotted/cross drilled brakes? why are they even sold?

 

Misuse of terms - it should've been brake force...

I've seen the debate on arguing that cooling is increased due to increase of metal surface area due to all the holes.&nbsp Braking (under race conditions) is usually very abrupt; brake rotor temps can go from ambient to up to 1000C in just a few short seconds.&nbsp Where's the advantage of cooling in that?



-Ted

 

Simple economics...
People want them.&nbsp This is the reason why we're having the discussion.&nbsp There's people out there that will tell you it's worth it.&nbsp Obvious, I don't. You're always going to have people who will listen to anything or just want to look cool.



-Ted

 

Same reason Altezzas and shopping cart rear spoilers are sold. Economics.

 

Before I forget, the obvious reason to drill brake rotors is to lower unsprung weight! This is probably why Porsche does it...



-Ted