do drilled/slotted rotors really help much on a street car?

[Voyn238]

I've been looking at www.irotors.com, and their drilled/slotted rotors as replacements for the stock units. I know that these are nearly a must on a race car, as the brakes are used almost constantly. But do they really help that much on a street car? When I use the brakes, it's not usually for an extended period of time - it's usually over with fairly quickly, doing the stop-light thing or going around corners.

I'm coming up on a pad change soon, and am trying to decide whether to bother with these things.


http://www.irotors.com/products/20-6.shtml

[jdk_ii]

I've been looking at www.irotors.com, and their drilled/slotted rotors as replacements for the stock units. I know that these are nearly a must on a race car, as the brakes are used almost constantly. But do they really help that much on a street car? When I use the brakes, it's not usually for an extended period of time - it's usually over with fairly quickly, doing the stop-light thing or going around corners.

I'm coming up on a pad change soon, and am trying to decide whether to bother with these things.


http://www.irotors.com/products/20-6.shtml

Not all race cars use slotted/drilled rotors, and certainly not a requirement.

Some solid vented rotors will out perform slotted/drilled rotors.

[Supra Bob]

My Dad always told that brake pads make more of a difference than the actual rotor they are on for street cars, and that slotted/cross drilled were good for applications that were ging to spend alot of time on the brakes and heat the rotors, as the drilling allowed for even expansion and the vents gave better cooling...

..now having said that, I've really no experience either way to prove or disprove that...its just kinda one of those things I took at face value...

So take that for what its worth...

[jdk_ii]

The two main components for improved braking is brake torque (more = good) and thermal energy transfer.

Larger caliper pistons create more directional brake torque.

Larger rotors create improved rotational torque.

Next is the eventual friction between the pad and rotor, and what type
of material of each.

Considering that high friction will produce heat, the rotor itself must
be able to slowly absorb heat, as well as quickly release it.

One can't get both at the same rate, so it depends on application.

A very heavy truck will want strong brake torque, and slow heat absorption. This is done purely through mass. More mass, less heat absorption. The rotor has very thick walls. However, they do not cool as quickly.

As for pads being the criteria, they may stop well at first, but if the
rotor can not cool sufficiently, one is chronically in brake fade.

[quick]

Cross-drilled rotors always crack under strenuous use (at the track). Even the big $$$ ones. They suck in that regard.

Slotted rotors can actually be beneficial as I understand it. Not sure about on the street though.

[Racefiend]

My 90 T-Bird had a problem (as most tbirds/cougars have) with warping rotors. Every year I'd have to replace rotors. A while back I finally got some cross drilled rotors. They have been on there for about 3 years and still no problems. I also used performance friction pads. Last month I bought a 93 tbrid to replace my 90 (it wont pass smog, ,so I'm retiring it). I never new how well the brake combo I put in the 90 worked until I drove that 93 around. Lack of initial bite and nasty brake fade compared to my 90. It's like night/day difference between them. Thats my experience with them. Hope that helps.

Christian

[SupraFiend]

As its been said heat is the problem. The stock mk2 brakes are too small for the car, they can't dissapate the heat quickly enough. Around town its fine but I find the stock brakes on a stock mk2 quite scary on high speed mountainous highways. They fade very quickly when they have to brake for a long period at high speeds going down a steep hill. The solution is to fix Toyotas mistake, iow get bigger rotors (talk to Jim) or to improve the cooling of the stock sized rotors. Cross drilled rotors used to be used as they allow for room from for the gases released from brake pads being heated up. Most modern brake pads don't release gases like this anymore. You still see them in use these days for 3 reasons. 1. Weight savings. Disc brakes on motor bikes and pedal bikes are usually cross drilled, this is just to keep their weight down. Bikes can get away with it as they're so light they rarely put enough stress on the brakes to over heat and crack them. 2. Ventalation and heat dissapation. This one is highly debateable as many would argue that since theres less metal on the rotor that they will actually dissapate less heat. I've seen quite a few instances supporting both sides of that arguement so I think it largely comes down to the quality of the rotor, but theres no doubt cross drilled rotors crack easier. 3. Asthetics. That Cross drilled look means serious racer boy so thats whey all the decked out civics have them :wink:

Personally I want to try plated slotted rotors (divited slots, not cut through). When your rotor does overheat your pads glaze over and thats the main cause of brake fade. Slotted rotors combat this by continually slicing off layers of the pads (the glazed part) like a cheese slicer. I'm hoping the slots will also make the air flow around the rotor more turbulent and improve the cooling of the rotor as well. Of course the down side to this is increased pad wear. But I'm to cheap (well more broke) to sink the cash in needed to get setup with a Jim King bb upgrade so I'm going to give the slotted rotors with some high temp pads a try. This is for my street/highway car so I'm hoping it will do the trick. If this was the car I'm planing on racing I'd already have the JK kit.

[Dean]

As others have pointed out, the brakes fade as the rotors get hotter.
So, it makes sense to try to keep those rotors cool.

One of the first tricks I learned after joining the Yahoo list was something to help cool the front rotors (which do 60-70% of your braking).
Simply bend the stoneguards/dust covers on the backside of the front rotors outward on the portion facing the front of the car. This helps to "scoop" air in towards the rotor as you move forward, helping to cool it much more. Be careful not to bend them too much. As you bend the front part out, the bottom tends to bend in closer to the rotor. Don't let it touch or the squealing will drive you crazy!

Another free mod that really works!

[quick]

The reason that the brakes fade is that the fluid is boiling. Consider upgrading to something like Valvoline Synthetic brake fluid. 500 degree tolerances should help. That, and construct some ducting.

[RWDCelicadude]

Suprafiend is exactly right. If you want serious brakes that work get larger non drilled rotors, if you want to be cheaper get good pads and duct cold air from the front bumper to the center of the front rotors, you should cut a hole in the scatter shield as close to the center as you can so the cold air gets drawn through the venting in the middle of the rotor and it cools evenly. If you just run cold air to one side of the rotor you'll risk uneven pad wear and possibly rotor warpage as one side will stay cool and the other side will get extremely hot. I'm working on doing this right now and should have it down in the next couple days. If anyone is interested let me know and I'll explain the whole thing once I get it working.

[Voyn238]

Okay, here's my current setup: KVR pads, Goodridge SS lines, Valvoline Synthetic brake fluid...

Here's what I'm thinking of doing: new KVR pads, drilled AND slotted rotors (hopefully best of both worlds?) from irotors.com, flush/bleed fluid, venting cold air to rotors via 1.5" tubing to each scatter shield center, and maybe add in a Mk3T brake booster and master cylinder (booster is bigger).

Chris and Jeff did the Mk3 booster/MC swap recently, and said it helped dramatically... If I can get the parts cheap enough, I might as well try it.


Sounds like a good setup to me... since it appears I am too late to get in on the Big Brake purchase, and also since I have 15" rims, not 16" (extra $1600 or so to replace).

[jdk_ii]

My suggestion is to stay with solid vented rotors.

The factory rotors are too thin, and by drilling/slotting
they will get hot faster. Even for slightly spirited driving.

I talked with JeffT about the MK3 brake booster. I believe
it's the increased vacuum boost that is making the improvement.
I've thought about this mod, but never got around to it.

The larger master cylinder of the MK3 will actually reduce
the line pressure (less brake torque). Stay with the 15/16"
bore MK2.

[Flyin' Hawaiian]

jdk_ii, do you know if the mkIII booster bolts right in without any mods to brake lines or fitment issues w/the cruise control? I'm assuming the booster is a bit larger than the mkII...
As for brakes, I'm running a divit-slotted rotor, one that was custom-cut out of a Brembo blank. I run this with Porterfield R4S pads(as well as Valvoline fluid and SS brake lines), and on the track I have no brake fade till the last 2 laps, and even then it's not really noticeable at all, just a slightly softer pedal.
For normal every-day driving, I think the stock rotors with some decent pads are acceptable.
And as for cross-drilled rotors, I have them on my Durango as well as my Toyota truck with 33's, and they have helped a LOT! The Durango's braking power is horrible, they should never have been sold with their puny front rotors! After 14k miles, they had to be replaced because of serious rotor warpage(had blue spots across the rotor from heat build up!). Replaced with cross-drilled rotors from Philsinc.com and it's finally time(at 73k miles) to get 'em turned because of slight pulsation.
The truck is still perfect with about 30k miles on em and a little stronger bite with less brake fade. The nice part of having 'em is they recover from brake fade a lot quicker than a solid rotor, I presume that it's because of the holes allowing cross-ventilation between the discs, and/or more open surface area for air to contact.

[jdk_ii]

jdk_ii, do you know if the mkIII booster bolts right in without any mods to brake lines or fitment issues w/the cruise control? I'm assuming the booster is a bit larger than the mkII...


It should be a direct fit, as the MK3 master cylinder is a direct
replacement for the MK2 (though the MK3 MC is not reccomended).

Actually, it has a larger diameter, which *should* mean it can
hold more vacuum, hence more power assist.

I have yet to do this, but will sometime late spring.

[Voyn238]

>>
The larger master cylinder of the MK3 will actually reduce
the line pressure (less brake torque). Stay with the 15/16"
bore MK2.
>>

Ya know, I've heard this for years, and it *still* doesn't make any sense to me. If I were using larger diameter brake lines, I would understand that *that* would reduce line pressure, because of the higher total volume, with the same amount of brake fluid being crammed into it. It seems to me that if line diameter (volume) were kept the same, and MC diameter (volume) were increased, you would be cramming more brake fluid into the same space, thus seeing an increase in fluid pressure.

Physics aside, I pose this question: If the 1" diameter MC were *worse* for overall braking ability than the 15/16" one, then why did they put it on the more powerful and *heavier* car?

Those are the two bits of reasoning that I put together to mean that the larger diam. MC is better...


but maybe that's just me....

[jdk_ii]

This article explains line pressure.http://www.hotrodheaven.com/tech/brakes/brakes4_index.htm

As for the exact reason the MK3 uses a larger diameter,
most likely it's the front caliper piston diameters are larger, hence more fluid.

Add the ABS component, and it manages most of the line pressure.

Many race cars use dual tandem master cylinders, and usually much smaller diameter.

[SilverMk2]

Think of it like this... You can physically only push so hard with your foot (i.e. you can only push say 100lb on the brake pedal) Now think about driving a stake in the ground. If you have a normal pointed stake (basically the tip area is small) you can push it easily in the ground (you have more lbs per sq in). Now if you try and push a blunt stake in your pushing force is divided up over more area (i.e less lbs per sq in). Basically all you are doing in a hydraulic system is transfering force not fluid. The actual pistons in the brake caliper move very little, so the fluid volume change is very small. The only reason I can think of why they used a different master cylinder was to balance the system out. MkIII brakes are similar but different to the MkII brakes. They might have had too much line pressure. The booster is their just to aid in braking effort.

[BlackSupra]

i upgraded the brakes on my last car.

It had 15/16' MC and a smaller brake booster.

I upped the brake booster and the MC to a 1inch item, changed to bigger calipers and rotors but kept the lines standard

HUGGGGGGGGGGGGE improvement.

I dont see why the MKIII Booster + 1inch MC would be such a bad combo?

[Crocket]

Ok, now for my 2 cents worth. I went through this same delimma several years ago, and here's what I came up with. Unless you are doing some serious autocrossing you don't need cross drilled rotors for a street car. Not only are they notorious for stress cracks in the vent holes, but when you actually think about it your reducing the available braking area by adding holes in the rotor. Your car will actually brake better and shorter without them. If you want better cooling and fade free brakes I say get them cadmium plated (prevents rotors from rusting, thus making sure the vents work at near optimum efficiency all the time) and add a flexible brake duct from the front bumper to cool them at speed. Slotted rotors arguably will make the car stop a little better, but the increase in brake dust and accelerated pad wear is why I decided against this option. As for oversized brakes, sure they look cool and will help the overall braking of the car, but their high price, and the fact that they add a decent amount to the unsprung weight of the car (making it accelerate a little slower) is why I decided against these.

My set-up is as follows: I went with plated Brembo replacement rotors (they are a little oversize I'm told, by a mm or two), Goodridge stainless steel brake lines, upgraded synthetic brake fluid (Dot 4 or 5 I forget, as opposed to the typical Dot 3 which has a softer pedal feel and lower boiling point), and Carbon/Kevlar KVR brake pads. All these items put together makes the car haul down speed like I have a shoot attached to the back of the car. It was amazing, and the pedal feel went from sorta soft and mushy to rock hard, even giving me informative pedal feed back which was lacking with the stock set up. To prove the effectiveness of these mods I did some brake testing after everything was installed and broken in. I got my 15 year old car (at the time) to brake better than 98-99% of all the cars in the car magazines, exotics included. I got a best 30-0 distance of 29 feet, bested by only two cars at the time, and tying another one. I decided not to try the 60-0 tests as I felt this was a little too dangerous to be doing on public streets, but I'm positive I still would have rocked more than 90% of the cars in the mags. And if/when I ever decide to do some serious track racing, I'll add some brake cooling ducts to the fronts, which should ensure fade free braking for most of what I'll throw at the car.

Like I said this is what I've done and had really good results with. Hope it's helped you out in deciding what's best for you. Good luck.

Sonny

[zo]

As far as I can tell, the only 2 reasons to drill brake rotors are 1. for weight reduction, and 2. for looks. Real race cars don't use drilled rotors. The holes don't really do anything for cooling. They crack easily and they lack the mass needed to absorb the heat from hard braking. Drilled rotors do not stand up to abuse and do not last as long as solid ones. But don't take my word for it. If you want to know the facts, and all the tech you can handle, check out the following link. The interesting discussion starts on the second page with the post by MaddMatt.

thread on altimas.net (http://www.altimas.net/forum/showthread.php?s=ba04305a502487cec1c1a470e6abbb89&threadid=32327&perpage=15&pagenumber=1)

Also check out the thread on corner-carvers.com referencing this 1st thread:

thread on corner-carvers.com (http://corner-carvers.com/forums/showthread.php?s=c85ef94e65a2c5b56ac28fe81e89f476&threadid=2002&perpage=40&highlight=drilled%20rotors&pagenumber=1)

those two together are probably several days of reading, but it should answer any and all questions people have about drilled / slotted rotors.

[SupraFiend]

upgraded synthetic brake fluid (Dot 4 or 5 I forget, as opposed to the typical Dot 3 which has a softer pedal feel and lower boiling point)

It would have been dot 4, dot 5 is a silicone, completely incompatible with dot 3 or 4.

[JZA-61]

I've got slotted rotors on the front of my car (currently with Bendix Metalking pads - soon to be replaced with Green Stuff). The slots probably don't make a huge difference in braking for street use. But they don't cost much more than non-slotted rotors and (unlike drilled) and last just as long, so why not give them a go?

- Justin
JZA-61 in production

[Supra GTR]

Sonny is right regarding the slotted vs. drilled. You do get less surface area on the drilled. They are prone to cracking.. even factory Porsche rotors will have stress cracks.

But some race cars did have these at one time. Not necessarily to dissipate overall heat, but to dissipate the heated gas that builds up between the pad and the rotor. now most are going with carbon rotors and pads. I happen to have a couple of carbon rotors from a BPR race car and they are not slotted nor drilled. Just pure carbon.

On my track mk2, I ran cooling ducts from the front of my car directly to the rotors for cooling. Still didn't help with brake fade. Ran Ford DOT brake fluid too. Which at the time was the best non-synthetic. Performance Friction uses their formula. Stopping just 3 times from 120 to 30 on the back straight at Mid-Ohio cooked the brakes. Had to run the entire track without using the brakes just to cool them enough to stop on the back straight.

For the street, if you're contemplating just replacing the stock rotors, go with a non-drilled/slotted rotor and concentrate on the pads, fluids, SS brake lines.

If you're serious about braking, I suggest the BBK that Jim was offering with slotted rotors. Or if you're into CNC work create your own. I would strongly recommend a BBK kit for all of you that have increased your HP with a turbo and/or engine swap. The mk2 brakes leave a lot to be desired.

[Suprabee]

Just wanted to thank everyone for their very informative insight in this post. I am also trying to decifer the drilled vs. solid rotor comparison. I think I'll go with the non-drilled Brembo rotors with KVR pads.
Anything more for me would just be overkill

Cheers!
Suprabee

[rsdeo]

Sonny is right regarding the slotted vs. drilled. You do get less surface area on the drilled. They are prone to cracking.. even factory Porsche rotors will have stress cracks.

But some race cars did have these at one time. Not necessarily to dissipate overall heat, but to dissipate the heated gas that builds up between the pad and the rotor. now most are going with carbon rotors and pads. I happen to have a couple of carbon rotors from a BPR race car and they are not slotted nor drilled. Just pure carbon.

Interesting discussion.

Okay from what I've read over the years (R&T, C&D, etc.) was that the crossed drilled and slotted discs were designed to dissapate the gases and worn pad material from between the the disc and pads as Supra GTR stated.

I've never driven any of my MK2s on the track, but a few people who have gone out for a cruise with me will know how hard and late into a corner I use my brakes.

As for the cracking I will find out for myself. My next set of discs will be crossed drilled and maybe even slotted. Nothing like trying things out for yourself. If they crack I will just replace them.

[StanS]

If you have an hour to spare, read this

http://www.stoptech.com/whitepapers/brake_systems_and_upgrade_selections_122701.htm

It addresses just about everything on the topic