Slotted & drilled rotors - worth it?

[jsmoriss]

For those of you that have switched from regular flat & ventilated rotors to slotted & drilled; did it make a difference?

As I've mod'ed my Jeep JK, I've been adding quite a bit of weight. The future purchase of a Chaser trailer won't help either. I'm wondering if a simple rotor upgrade (and probably pads too) will make a difference, or if I need to think bigger (larger rotors and calipers). I don't have much room left those since I'm staying with 16" wheels, so can't really go up much from the stock rotor size...

Thanks,
js.

 

[spressomon]

I faced the same problem after modding my '99 LC 100 with heavy equipment and pushing to 35" tires. I have had great success with cryo'd rotors (ART) on an A6 V8 Audi (notorious for eating rotors) and Saab 9000.

I installed the slotted ART cryo'd rotors almost 2-years ago along with Porterfield carbon/kevlar pads and the results were/are amazing. Significantly more peak braking power without the expense and complication of going to a larger disk and caliper upgrade path. And no problem whatsoever off-road...and I drive alot of miles of gravel/dirt.

If you don't see your rig call them. They don't list my LC rotors but they were able to set me up.

And regardless you should get the electronic brake upgrade on your AT. I did and it makes a big difference on & off-road.

http://www.appliedrotortechnology.com/

 

[1leg]

I sware by Drilled and slotted rotors, My wife is notorious for wraping rotors on her 98 Camery. A buddy suggested drilled and slot rotor. She is now on here seconded pair of pads with out turning the rotors. the first set of pads w/drilled and slot rotors last almost 4 years. I also suggest that you don't buy the cheap pads at Pep boys or the like. I alway go to Napa and buy the expensive pads. I don't know the diffrents between the brands but they seem to last longer for me.

Drilled and slotted :bowdown:

 

[nat88toy]

on a car yes they make sense on a truck that is going to see mud...NO! mud will pack into the slots and drill holes just worthless, ask me how i know:sombrero:

 

[nat88toy]

I sware by Drilled and slotted rotors, My wife is notorious for wraping rotors on her 98 Camery. A buddy suggested drilled and slot rotor. She is now on here seconded pair of pads with out turning the rotors. the first set of pads w/drilled and slot rotors last almost 4 years. I also suggest that you don't buy the cheap pads at Pep boys or the like. I alway go to Napa and buy the expensive pads. I don't know the diffrents between the brands but they seem to last longer for me.

Drilled and slotted :bowdown:

catch 22 on the pad quality... i have always $ the cheap pads at napa and replaced them twice a year and have gone well over a 100 miles with out having to replace the rotors, the pads are so easy to swap out while the rotors are kind of a pita so id rater just buy cheap pads and let them where out.
i had once $ the best of the best pads and they lasted a good while but warped my rotors.
but this is just person preference I am sure it may be different from vehicle to vehicle and what kind of driving condisions you get your self into

 

[goodtimes]

One of my favorite debates.

I spent about 5 years in the braking industry, I was not on the design side, but I spent enough time with the rocket scientists to pick up a thing or two.

Long story short: Drilling a vented rotor can reduce temps by ~200*F. The holes typically have the edge broken with a strait 45* or 60* chamfer. This can lead to cracking...a radius would be better (but is cost prohibitive).

Slotting does not significantly reduce temperatures.

Both slotting and cross drilling do offer one big advantage: an escape path for outgassed particulates (brake dust). This allows the pad a fresh "leading edge" by helping eliminate the boundry layer of outgassed particulates between the pad and rotor. Slotting is more effective at this than cross drilling....but remember the temperature advantage of cross drilling.

With regards to rotor life, the casting is infinately more important than drilling &/or slotting. Cheap rotors are just that...cheap. And usually from a off shore foundry. Quality castings are much more expensive than most of what comes out of China or Korea (we used to use both in the economy line rotors). NA castings were much better, and used on 100% of the premium line rotors (that we sold).

Also keep in mind that not all pads are created equal, and not all pads are appropriate for all applications. They all have a certain heat range in which they perform at their best....so care must be taken when looking at aftermarket pads. As much as I hate to admit it....OEM pads are hard to beat for performance, longevity, and low dust.

Now, if you are looking to improve braking performance...there really aren't many options that are affordable.

You can increase rotor size, thereby increasing the leverage the pads have on the rotating assembly. You'll need bigger rotors, different calipers, brackets, and probably need to tweak the brake bias.

You can increase the line pressure. This involves a different master cylinder, more leverage to the existing master cylinder, or bigger bores in the calipers &/or wheel cylinders...and don't forget the tweak to the brake bias to keep it balanced.

You can change the coefficient of friction between pad and rotor (or drum and shoe). Reducing heat is how cross drilled rotors accomplish this...different type of material used in the pads, different casting, removing the boundry layer of particulates, etc will also contribute.

Really, the first option is the best way to accomplish the goal...unfortunately it comes with a big price tag. Look at companies like Stop Tech LLC, etc...they offer some "big brake kits" (not to be confused with similarly named kits from pep-boys etc, which only consist of direct replacement parts) that come with everything you need.

 

[TheMike]

.....the future purchase of a Chaser trailer won't help either......

Spend the little extra money and get the Chaser with brakes. Problem solved from this end

My LJ Rubi stops way better with the Chaser attached, at over 2k lbs, and brake controller properly set. WAY BETTER!

 

[jsmoriss]

Thanks to everyone for their replies!

As a first upgrade, I think slotted/drilled rotors + carbon metallic pads looks like the way to go. Applied Rotor's kit spressomon suggested look great. A little expensive, but that's always secondary for me (quality being first).

I can't really increase rotor or caliper size. Only a few 15" wheels fit on the JK, and I've decided to standardize on 16" wheels (the JK came with 17" wheels). I do some off-roading a couple times per year, and need the extra sidewall.

As a second upgrade I can always look at upgrading the calipers themselves, and perhaps boosting line pressure. We'll see how the first upgrade performs. From what I've read, there's a dramatic difference with the ART rotors...

Thanks!
js.

 

[Andrew Walcker]

I'm running the DBA (Disc Brake Austrailia) Gold rotors up front with stock LR pads and am very pleased. Hard to say it is better than stock because my fronts were pretty shot when I changed it out. I won't hesitate to go with the DBAs in the rear when the time comes.

 

[Michael Slade]

I'm running the DBA (Disc Brake Austrailia) Gold rotors up front with stock LR pads and am very pleased. Hard to say it is better than stock because my fronts were pretty shot when I changed it out. I won't hesitate to go with the DBAs in the rear when the time comes.

Yup, same here.

 

[ntsqd]

One thing that Goodtimes touched on that probably should be expanded is that with these different operating temperature pad options comes the need to know where you're going to be using them. For instance, putting a Ferodo DS-11 pad compound in a 4x4 would result in a gross reduction in braking power because the 4x4 would never ever get that ancient compound up to operating temperature.

I've run into this exact thing in using the original Performance Friction pads (when they first came out) in a 4x4. They worked wonderful in traffic. Couldn't get rid of them fast enough off road. I say original compound because I do not know if they've changed their formula or not.

I would say that it is rare that a racing pad will have it's sweet spot temperature range lower than a stock pad. That is not the emphasis of the aftermarket vendors. They are trying to offer better on-road braking to the performance driving crowd, which means a higher Friction Coefficient at street driving brake temperatures and an increased resistance to fade.

BTW, the idea that rotors need holes to bleed off gases generated from heating up the pads came about with older compounds like those DS-11's. Modern pads normally do not generate such gases in any great quantity if they have been properly bedded, which renders the holes to be nearly only cosmetic.
Also keep in mind that in a drilled vented rotor it is extremely rare to see the inside hole edges deburred. They are no less impervious to forming cracks than the outer hole edges. So even if the visible hole edges are radiused, the job is still only half done and isn't likely to be finished.

FWIW I spent 2 years in the design of disc bits. Hardly qualifies me as an expert, but does offer some insight.

 

[madizell]

Thanks to everyone for their replies!

As a first upgrade, I think slotted/drilled rotors + carbon metallic pads looks like the way to go.

I would not use metallic pads for off roading or generally slow driving. Metallic pads require high contact pressures and high heat to work. These pads were developed for road racing. Stick with OEM style pads, which are mostly organic or hybrids. Dunk metallic pads in mud and they just about stop working.

 

[jsmoriss]

I would not use metallic pads for off roading or generally slow driving. Metallic pads require high contact pressures and high heat to work. These pads were developed for road racing. Stick with OEM style pads, which are mostly organic or hybrids. Dunk metallic pads in mud and they just about stop working.

Good point. What about carbon-kevlar? :-D

js.

 

[R_Lefebvre]

I agree with NTSQD.

Drilling rotors is old fashioned and unnecessary with modern pads. I can't see how it could be suggested they decrease rotor temps by 200F and I'd like to see the data on that.

Removing mass from a rotor could hardly be argued to reduce peak temperatures during a braking event. Basically the kinetic energy of the vehicle of a given speed and weight is turned into thermal energy in the rotor of a given weight which leads to a resultant temperature rise. Reducing the weight of the rotor necessarily increases the peak temperature.

Similarly if you're talking about long term steady state temp such as on a racetrack, the holes would have to be quite large to offer more surface area for convective heat transfer than the surface area removed on both faces when you drilled the holes.

Holes are really only cosmetic anymore. Slots do have some application on rally cars because they help clear the mud from the calipers. However, you will not see holes or slots on almost any serious race car.

The disadvantages of holes, besides the cost, is that they lead to premature rotor cracking, and reduced pad life due to the "cheese grater effect".

Yes, Porsche puts drilled rotors on their cars. They also put on fancy wheels and beautiful paint jobs and those don't make the cars faster either.

 

[slooowr6]

I don't understand why eveyone keeps saying drilled rotor is easier to crack? I've drilled rotor on my A4 for 5 years with 50k on them and they are not cracked. My A4 is my DD and I drive it like a normal commute car. I did see drilled rotor cracked BUT that is on a full race car with stripped inside and roll cage. I'm not sure if it'll help braking or not but I'm pretty sure they will not cracked if I put a set on my Tacoma.