Drilled and Slotted Rotors

[Norm Peterson]

This makes no sense from a purely economical standpoint. You mean to tell me that Ford, Chevrolet, Jaguar, Porshe, BMW, Mercedes, Lamborghini, Fiat, et al, are going to waste hundreds of thousands (or millions) of dollars of engineering just to install an "appearance mod"?

That's exactly what I'm saying. The days of needing holes so that pad outgassing has a place to go are well behind us.

It doesn't add anywhere near that much cost to get a rotor supplier who already has the necessary equipment to set up for production runs of different rotors.

The average consumer is easily conned. Ever hear of tornado air intakes? Throttle body spacers?

Not to mention all of racing circuits around the world who use drilled rotors....I'm sure that's just for marketing too...

Not sure what you're trying to say here, but in racing mission-critical wear components tend to get changed out after every race. Would you seriously consider replacing your own car's rotors after a single track day? After just one multi-day event at most? If there was no visible damage?


Norm

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[Evolvd]

The average consumer is easily conned. Ever hear of tornado air intakes? Throttle body spacers?

Yes, but those were never sold by OEM auto manufacturers...so I don't know where you're going with this.

Not sure what you're trying to say here, but in racing mission-critical wear components tend to get changed out after every race. Would you seriously consider replacing your own car's rotors after a single track day? After just one multi-day event at most? If there was no visible damage?


Norm

I was going with the fact that legitimate race cars run drilled rotors...so apparently they aren't so bad for braking as some would want you to believe.

 

[Norm Peterson]

Yes, but those were never sold by OEM auto manufacturers...so I don't know where you're going with this.

I was going with the fact that legitimate race cars run drilled rotors...so apparently they aren't so bad for braking as some would want you to believe.

We probably wouldn't have seen drilled rotors if it wasn't for drilling to be the easy fix back when brake pad outgassing actually was a serious problem. The image caught on, and I doubt that many people understand either the thermal transient tech or the fatigue tech involved well enough to have an informed opinion.

Fatigue failures are not pass/fail in nature; something may hold up just fine under less severe heat cycling, or very well under more severe cycling until it suddenly doesn't.

Heat cycling can even get surface cracking started in plain rotors, where there aren't any built-in crack-start locations. Here's one of mine from a couple of years ago, that's never seen more than 130 mph at the beginning of any braking event. If I can catch a fingernail anywhere on a rotor, it and its mate on the other side of that axle goes in the scrap heap regardless of how much measured thickness above minimum remains.

Even track pads can crack from the heat. Note that every hole has a crack starting at or near the middle of the outer edge (closest to the pad OD).

Norm

 

[JamesinLittleSilver]

Drilled rotors are not going to be as durable as non drilled rotors. Lower quality rotors that are drilled are worst...really good quality rotors that are drilled will last better. But a lot is for show now.

 

[mustang_guy]

Surprised no one mentioned less surface area for braking too with drilled. Slotted or blanks imho are the best way to go.

 

[Norm Peterson]

Something I ran across while cleaning up my inbox today, seemed timely. Emphasis in the text mine.

It's not mandatory . . . yet.


SAE J2928: Rotor Standards
In 2012, an aftermarket rotor testing procedure was approved by the Society of Automotive Engineers (SAE) titled, “J2928 Brake Rotor Thermal Cracking Procedure for Vehicles Below 4,540 kg GVWR.” The document was a marriage of current industry tests and best practices. The goal of the document was to make a standardized test that could evaluate an aftermarket rotor’s ability to resist cracking using a dynamometer.
For technicians and drivers, J2928 might change the decision-making process of what rotors go on a vehicle.
The Test
SAE J2928 test procedures subject a rotor to 150 heat cycles. A heat cycle is when a cold rotor is brought to a high temperature. During a heat cycle, a rotor will expand and contract. This can create fatigue in a rotor that can cause cracking and structural failure.
During the 150 heat cycles, the rotor is inspected; this includes for dimensions and any visible signs of damage. The objective of the test is to thermally and mechanically stress the rotor so any deficiencies in the metallurgy or structure are exposed. J2928 also covers how to document and classify cracks.
Unlike a USDA grade or a movie rating, SAE J2928 is just a document of recommended procedures. It is up to the industry to adopt and embrace these tests. The supply chain could benefit by comparing and evaluating rotor manufacturers to assess consistency and accountability. This will directly benefit shops.
The Marketing of J2928
No rotor manufacturer can claim that passing the 150 heat cycles means its rotors stop sooner, make less noise or last longer. J2928 does not test for this. Nor can a manufacturer make the claim that since its rotors are tested with J2928, they meet a government standard set forth by DOT or NHTSA.
What a rotor manufacturer can claim is that its rotors were tested using SAE J2928 and assessed using accepted industry performance criteria; or, that its rotors meet industry-accepted pass/fail criteria regarding number of heat cycles without severe cracks.
Bottom Line
SAE J2928 is a step forward because it helps everyone in the supply chain speak the same language. It also sets criteria when it comes to measuring aftermarket rotors.
SAE J2928 is:
· An aftermarket rotor-testing procedure.
· A series of 150 heat cycles performed on a dynamometer.
· A measurement of the thermal and structural adequacy of a rotor.
· A method of measuring, classifying and documenting cracks in a rotor.
· A tool for the supply chain to perform quality control on the products it sells.
· A way to compare an aftermarket rotor to an OE rotor.
· A measurement of rotors for runout and thickness variation.
· A specification for a rotor to meet a percentage of the original rotor’s weight.
· A specification for a rotor to be within certain dimensional tolerances.
SAE J2928 is not:
· A way to police bad rotors.
· Mandatory for all manufacturers, including OEMs.
· A measure of on-vehicle performance or stopping distances.
· A measure of noise or durability.
· A “certification” or “approval” of a rotor.
· Performed on a vehicle.
· A determination of the design of the rotor’s fins.


Norm

 

[ForTehNguyen]

many racing teams out there used slotted only. Drilled rotors will crack over time, if a crack joins up two holes it gets even worse

 

[chedder]

I track my GT extensively here in the NW. I have had drilled rotors with filled holes in a regular session then crack. I now have RotorPros slotted front and rear and have no issues stopping hard from 150mph down to 65mph or also hard braking from 110+ down to 35mph 15 seconds later going down hill. Love them!

 

[Dr. Norts]

R1 concepts Premier Series rotors are good stuff. I have ran them for years and actually just installed a set with the new GeoMet coating on my FX35.

I've never had a pair of these warp or wobble or do whatever shitty rotors do.

To the OP, go drilled and slotted if you like the look. I had a set of the R1 drilled/slotted onmy G37S for lots of hard driving without a single crack or ill effect due to being drilled.

 

[Grintch]

For the "no drill" folks the only thing I have to bring up is that Porshe, BMW, Audi, and many others sell their cars with OEM drilled/slotted rotors...so with millions spent in engineering I'm betting they know a bit more about how effective at braking they are than us.

I've been running the Rotorpros drilled/slotted and have no issues on mine after 4K+ miles.

Marketing. They also sell poor performing large diameter wheels, because people think they are cool/look good.

In the racing world it's is well known that with modern brakes, drilling has little advantage yet greatly increases the rate of rotor cracking.

But the OP said he was buying them for looks and that he did not want or need performance brakes.

 

[AmericanLegend]

Drilled rotors do little to dissipate heat or gas (in fact, slotted rotors don't offer that much benefit either). Drilled rotors do, however, create hot spots for clamping stress and offer many potential failure points for cracks to propagate.

Had a set of drilled 1996 Cobra rotors develop many small cracks which were propagating from the holes.
I'll never buy drilled rotors again.
I've had good luck with slotted only rotors.

 

[Waldo Jeffers]

Besides, I only look for slotted two-piece rotors that help reduce the ridicolous heavy weight of the one-piece- stock and aftermarket rotors.

Anyone knowing of more good parts, not only those from Stoptech and Girodisc ? (Brembo is just too expensive)

 

[Voo Doo]

Just the Bling

I know what the knowledged guys are saying about holes but......I bought drilled and slotted (haven't got new pads yet) for my GT PP. it's strictly an aesthetic thing for me. Never track my car, never will, put maybe 5,000 mi on a year. In Mexico for 5 months.

I would venture to say....we all bought a brand new car....then we added some special parts, mostly for the Bling and to personalize our ride. Did we need them, hell no......did we want them, oh ya!

It just matters what you use your car for....shows...then drilled/slotted for sure.

The GT350 and 350R come from the factory drilled .......yes? What are Fords ideas about that? I donno ??

 

[Evolvd]

Well if you go by what others think it's just so Ford can sell more cars lol

 

[NightmareMoon]

Porsche rotors crack at the track, Ferrari rotors crack at the track, and rumor is their engineers have admitted that they're only for aesthetics and to meet their high-dollar customer's visual expectations.

High-dollar race teams (Porsche) can use whatever they want if they're replacing the rotors every race anyways.

I laugh when I see drilled rotors at car shows.. To me drilled look is all show and no go.

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