Brembo drilled brake rotors -- "long term" satisfaction?

Michael,
I purchased drilled and slotted Brembo rotors for a Honda Accord. I noticed immediately that they was some "humming" noise on hard applications of the brakes. I presume this is from the slots. These were purchased from the Brake Warehouse, and they did a nice job, all holes where chamfered, as where the slots. Over the course of putting 70k miles on them, they did warp ever so slightly (it was detectable on hard applications). So when I had new pads installed, they took a slight cut off them to "true" them up. The 70k miles of wear, plus the slight cut taken, did make the slots very shallow, which eliminated the humming noise.

I would be inclined to get the factory drilled rotors from Brembo, as that would be preferable. I would tend to avoid slotting, if you have the holes, then it becomes pointless. Some say the slotting is more effective, but the noise bothered me.

Dave

 

Dave,

The slots are to remove the glaze that can build up on the pads. The cross-drills help cool the disks down

Matt

 

Matt,
I have never heard that. The "conventional wisdom" I have heard is that both the holes and the slots were to allow a path for the "off gassing" of the pads. The cooling aspect of either modification is negligible, unless you can duct air to where it can do some good. How would the slot remove glazing? They are typically chamfered, so there are no sharp edges. If it did that, it would wear through a set of pads awful quick!

Let's face facts, most do this more as a cosmetic improvement rather than performance. The rotors are already axially vented, and removing metal by drilling and slotting, removes more of the potential "heat sink" properties of the metal. Adding air ducts seems like the way to go, but when my rotors need replacing I will get the Brembo factory drilled ones, just cause the look cool.

 

Dave,

My comment was based on a artile I read some time ago in R & T, not that they are ever wrong I would tend to agree with you on all counts. I favor the sloted and vented. Cross-drilling just weakens the rotors.

 

Matt,
What has your experience been with slotting? Have you noticed this "humming" noise I experienced with hard braking? Has anyone else had any noise issues with slotting or drilling?

 

Slotted rotors tend to hum. The point of slotting and cross drilling is to allow the outgassing of the pads to escape, eliminating the "air hockey" effect of the pad floating on the disk. This is the main reason brakes fade when they get hot, the pads outgas then float on the gas. More expensive pads are sometimes "precooked" in hot ovens to allow most of the outgassing to occur there berfore being installed on the car. Of course larger well ventilated brakes heat the pads less on cause less outgassing.

 

Mike,

Buy what you like, the Brembo rotors are a good choice. For street driving, the holes are cosmetic, and most likely will not degrade the longevity.

As for slots and humming, I have not experienced this, though I won't discount the possibility. Slotting, especially under race conditions, will slightly increase pad wear rates. It does indeed "clean" the pad surface of material that would otherwise build up in the interface and scour the rotor surface, ultimately decreasing rotor life and friction characteristics. In race applications. Properly done, the bedding process removes the "gasses" in the pad, so outgassing is not an issue for a pad in the correct application. Outgassing is an issue if one takes a street pad on a commuter car to the race track. OEM Ferrari pad manufacturers realize the car will see high speeds and design the pad to handle higher than normal road car temperatures. A race pad will have even higher (1000 degF +) temperature capabilities.

Pad "glazing" is typically only an issue when bedding in new pads. Go too easy on them and you will negatively influence the friction properties. Go too hard too soon, and you'll break down the pad material, again making the new pads useless.

So slotting doesn't remove the glazing, but I can see how a journalist can get engineering terms and technology confused without intent to misinform.

Street driving is a factor of 100 easier on rotors and pads, though have other issues race engineers aren't concerned with (like noise).

Best regards,

Rob Schermerhorn

 

I've had my Brembo drilled rotors on all four corners of my 308QV for quite some time and through several track days, and am still very happy with them. The holes do aid in additional cooling on track days. I purchased my rotors through Elite in Canada. I use them with Porterfield R4-S pads.

 

Dave,

Rob's post was excellent on the clarification on the "cleaning" of the pads by slots. I only ran stock rotors on the Ferrari, I experimented with rotors on a Celica All-Trac that I had. I ran vented and drilled and noticed that the rotors would warp and made a clicking sound. Then I ran the stock rotors which were just vented and they were fine. When I switched to Vented and Sloted, I did notice the hum.

Matt

 

holes do NOT aid in additional cooling.

cross drilled (holes) = weight savings
slots = additional cooling

Also, with R4S pads, they work fine on the street, even though a bit dirty, but I cannot see these lasting on a track even for one day. You should try swapping them out to R4's for track days if not something else.

 

I installed slotted rotors on my Range Rover and have been very pleased with the results.
I have also bought cross drilled Brembo rotors for my 308.
I have yet to install the rear rotors, but had installed the front rotors and used the car for several months, and was also very pleased.
Of course anything would be better than the old worn rotors and pads that were on my car...
At this point I am doing a complete tear down and rebuild of the suspension and under carriage of the car as my winter project.
For what its worth, the stock size Brembo rotors are only offered as standard.
Slotting or cross drilling of this rotor is offered by after-market resellers.
The "only" place that is approved by Brembo for this service is Race Technologies.
These rotors can be purchased through Evo Sport...
These cross drilled rotors really start to shine when you install brake cooling ducts so you can take advantage of the cooling effect of the air running through the holes and out the vents.

 

As is the norm, Rob S is spot on in his assesment. One subject that has not be touched upon is that of thermal shock. You can vastly increase the life of both your pads and rotors in 2 ways:

1. Don't get them wet when they are hot. Sounds simple but it is easy to do without thinking about it.

2. If driving fast (on a track or similar) LET YOUR BRAKES COOL BEFORE STOPPING. If you are tracking your car, once the chequered flag comes out, take an entire lap at a pace where you will not need to use the brakes once. This goes a huge way in making your brakes last.

On the second point, a few years back I was doing some testing with AP brake engineers in the UK. Using road cars, we found that by taking a single cool down lap after 15mins of hard track driving, we could increase brake pad life by 30-40%.

 

The more I read about cross drilled rotors, the more I think it is bunk.

I've read alot about them on corner-carvers.com, and the general consensus among racers is that they are almost purely cosmetic. Will not improve cooling, stopping distances and if anything, may lead to cracked rotors.

Here are links to a couple good articles (appeared in grassroots motorsports) about brakes:

http://www.teamscr.com/grmbrakes.html
http://www.teamscr.com/rotors.html

From these articles and others, it seems like the best way to improve braking are:

1) Better tires
2) Race specific pads (assuming you are racing).

Mike, with regard to the rotors you are considering: Well, it seems to me the price is pretty reasonable for rotors. If you can get non drilled rotors for the same price (or less!), I would definately go for it. If you can only get the cross drilled, I would still consider it, but realize that you will probably not improve breaking performance with them.

Hope this helps.

Dom

 

Wait a second. My 308 (It's a GT4) has brake cooling ducts. I noticed them the first time I took off my wheels. Are these present on all 308's? Or just GT4's? Or is it something that was done by one of the cars PO's?

Dom

 

I understand the Brembo rotors drilled from the factory are cast that way. This is why they don't crack around the holes! It's not a good idea to drill rotors not designed for it.

 

Actually, If I may, I would like to correct what Matt said regarding the purpose of drilling rotors, the holes might indeed help cooling but its not their main purpose, The main purpose for drilled rotors is to eliminate water on the bracking surface. This started in the early 70's in motorcycle racing. Under the rain, when a rider would apply the brakes and the disks were wet, there was a delay between the actual pushing of the lever and the resulting braking action which happened suddenly and without moderation with the rider sometime falling as a result. It was discovered that by drilling the rotors, water was displaced almost immediately resulting in a more timely and progressive bracking action. Under dry weather however, non drilled rotors are superior in braking action because there is a larger area under the pads. Also, drilled rotor are harder on the pads. The fact that a lot of street cars have drilled rotor is mainly for "looks" but is not really needed is street application for performance!

 

I've found Porterfield R4-S pads work QUITE well, and one set has served me for several track days. They are DESIGNED to be used for street and light track. It's not a competition car, nor do I drive it like one.

I do believe that adding cooling is a specific benefit of drilled rotors other than making them more effective in wet conditions, unless you're just wanting them for cosmetic reasons. Even the ENZO uses holes in their carbon brake rotors. They aren't to make 'em lighter...

Just making that one change (cross-drilled Brembo rotors) made a difference in how long I can drive on the track before getting start of brake fade.

No offense meant, Randy, but I'm speaking of personal experience with MY Ferrari. It may be different than with your Honda.

 

Mike Charness,

Nice to hear about your experience.

Did you read my links above? According to them, cross-drilled rotors should not make much of a difference. Of course, theory and reality are sometimes two different things.

When you changed your rotors, did you change anything else (i.e., brake fluid, pads, tires, etc.)? I guess what I'm getting at is: was it a controlled experiment?

I've only done one track day with my GT4, using stock rotors and Porterfield R4-S pads. No problems with brake fade. Did have a problem early on with boiling brake fluid, but once I bled the brakes, I was good to go for the rest of the day.

Dom

 

Can anyone confirm that F1 cars do not use cross drilled rotors?

What about other race-type events. Cross drilled? Slotted? Regular?

Dom

 

Dom:

Between track events (both at the same track), the only change was the rotors. I already had R4-S pads on there before making that change. For both of these two events, I did as I usually do, just "turkey baster" out brake fluid and do a partial change just before the track event.

By the way, nice bit of work on your profile graphic and avatar!

 

if you want rotors that cool just a bit better, get blanks with slots only. there are other factors in increasing your ability to stop with the swap out. one of the main factors is the newer metal vs. the older and fatigue over the years, others deal with the makeup of the metal itself.

the R4S's can work fine on the track - hence light track events. I've just had too many occassions where they end up on the sides of cars after four sessions and the pads are down to metal. aggressive driving and aggressive braking are two different things and these guys were very aggressive on the brakes. luckily I brought spares on all occassions in case I, or others, run into these situations.

why the enzo has holes is not really the case here. the enzo has lots of weight savings all over the place, which include the make up of the carbon-ceramic brakes themselves.

regardless.. I'm glad you are happy with what you have and that they work well for you.

 

solid. full out solid rotors. anything less and it reduces the rotor mass, which in turn reduces the amount of heat that the rotor can hold. if any particular team utilizes any trick rotor, it would be slotted only, but I have not seen this at all.

the f1 cars use solid carbon/carbon rotors. they take approximately 6-9 months to make ONE rotor. (I'm sure that they make more than one at a time too!)

if some other race team out there uses something else... then I'm unaware of it, but I'm not an expert on what all teams and racing sanctions utilize.

 

Mike,
After intensive discussions with the Brembo guys, I decided to go for slotted rotors on my 92 348ts. So far no regrets. It brakes like hell, no fading and the pedal touch is great. Philippe.

 

As I addressed in my previous post in this thread and others, slots are for removing pad dust, thereby 'cleaning' the surface of the rotor, and reducing the scoring that aggressive, high-temperature pad compounds will frequently produce. They do not aid cooling.

Only proper air ducts and/or water will aid cooling (assuming the rotor is a large enough mass to begin with by design, usually not the case with road cars, though newer Ferrari's are the exception (3x8, TR only marginal for track duty)).

Cross drilling is indeed a weight saving measure, but only in small-bore, light-weight race cars, or qualifying specials. For road cars (including Ferrari, Porsche, et. al.) drilling is a marketing decision only (Bling-bling).

So if you want cross drilled rotors for your road going Ferrari or other street car, go for it, impress the enthusiasts, the ladies, and the great unwashed. You're not hurting a thing or decreasing your braking capabilities on the street.

In fact, just keep a wary eye on cross drilled rotors on the track, as they will eventually play 'connect-the-dots'. Especially the outermost holes cracking to the outside diameter of the rotor. Don't worry about small 'spider cracks', specifically when the rotor is 800 degF or so. Worry if they're wide (0.08 mm) when the rotor is cool.

Have fun, good thread.


Best regards,

Rob Schermerhorn