slotted vs. cross drilled rotors?

[SandEagle]

looking at rotors. read that drilled isn't good as it could cause rotors to crack. sounds like bs. what is your take? i have the option to even go drilled and slotted.

 

[Kelvrick]

Drilled is fine if that was the way they are made, not if they were drilled after the fact.

Usually they're considered more show though, I've found unless you're doing a good number of track days a year, solid is fine.

 

[Tsavo]

looking at rotors. read that drilled isn't good as it could cause rotors to crack. sounds like bs. what is your take? i have the option to even go drilled and slotted.

Are you tracking or racing?

Anyway, drilled rotors can fail.

Beyond that, I say save your money, and spend it on actual go-fast goodies. Like giant rear wings on a FWD car, or a "stance" kit, or some racing stripes.

 

[SandEagle]

Are you tracking or racing?

Anyway, drilled rotors can fail.

Beyond that, I say save your money, and spend it on actual go-fast goodies. Like giant rear wings on a FWD car, or a "stance" kit, or some racing stripes.

no tracking, no racing. just need rotors for my daily driver. i plan to put bigger tires/wheels and want to replace the rotors/suspension/pads. got a set of posi-quiet ceramics on order and thinking of just doing drilled rotors.

 

[Greenman]

It seems like you're solving a problem that doesn't exist.

 

[Meghan54]

I'd go slotted before drilled, but I wouldn't waste my money on either with a daily driver, esp. using ceramics. I'd just find out if you can obtain a set of Brembo blanks for your replacement discs and call it a day.

Ceramic brake pads are not the be-all and end-all of brake pads...far from it. Remember, ceramics were developed when asbestos was on the verge of being banned from use in brake pads, and car manufacturers wanted pads that lasted a long time, had low NVH (noise, vibration, and harshness) and low dusting qualities. The first ceramic pads were used on Honda Accord, Toyota Camry and Ford Taurus...not exactly high performance cars but cars with drivers who wanted brake pads that worked without making themselves known. (This according to Akebono's web site.)

Personally, a dd is perfect for ceramic pads. Low noise, long life, low dusting. But if you're looking for increased performance, you need to pay attention to the friction rating every brake pad has to have assigned by the DOT. The ratings, done in a two letter rating that's painted on the pad's edge, are typically EE, FF, GG. The first letter represents the coefficient of friction (CF) when cold braking, the second is hot braking CF. There are pads that are rated like FE, which represents better cold than hot braking CF, which indicates it fades a bit when hot. The letters do have a fairly wide range of friction within them, so they're just a guide. Not all EE's or FF's brake the same.

For instance, when we bought our Silverado, the GM dealer had just replaced the front pads and rotors..the rotors were so new the original machining marks were still plainly visible. The pads were AC Delco OEM pads, rated FF. I replaced them with some Hawk LTS pads, also rated FF, but the initial bite was vastly improved with the Hawks. Much less fade, esp. when we had one of our trailers or our boat hanging off the back of the truck.

Good luck!

 

[Jimzz]

Just get a regular premium rotor like the raybestos Advanced Technology or centric High Carbon rotor.

 

[RGN]

Pretty much everything Meghan54 said.

 

[KentState]

You will notice that a lot of race cars use some form of slotted rotors, not drilled. For street use, just regular rotors are the best. More surface are is what you want, not missing material.

 

[SparkyJJO]

I have slotted/drilled rotors on my Trailblazer (of all vehicles lol). Simply because I got the set of rotors and ceramic pads for under $200 from Brakemotive. Decent quality stuff and costs less than going to the store and buying a bunch of rotors and pads. Don't really care about the slotted and drilled part, but they are and they work fine. No cracking on my previous set, or anyone else I know of who has a set of their rotors on whatever cars they have.

 

[SandEagle]

You will notice that a lot of race cars use some form of slotted rotors, not drilled. For street use, just regular rotors are the best. More surface are is what you want, not missing material.

thanks. i guess you are right. plus it would be cheaper. $400 for drilled rotors is crazy. with new wheels coming, my brakes will be showing more so i wanted something cool and practicle.

 

[xSkyDrAx]

I think the only time I've seen drilled rotors on cars are typically in the higher end luxury/performance vehicles. Slotted are more common on less expensive cars (mine comes with them) but you won't notice any visual difference between them and regular rotors.

 

[madoka]

I just looked up my Nissan and found it comes standard with cross drilled rotors. I don't think I ever even noticed. Then again, it took me six months to realize it has heated seats.

 

[cbrsurfr]

I've seen drilled crack on a racetrack. Slotted allegedly wears the pads out faster. For a normal DD, regular is perfectly fine.

I've seen slotted and dimpled also being offered as an alternative that shouldn't crack but I've never tried them.

 

[monkeydelmagico]

thanks. i guess you are right. plus it would be cheaper. $400 for drilled rotors is crazy. with new wheels coming, my brakes will be showing more so i wanted something cool and practicle.

Slap some paint on your calipers for the "cool" your looking for. Maybe a couple stickers too while your at it.

 

[JoLLyRoGer]

Without going into any of the technicalities it comes down to this:

Blanks > *

Slotted > Drilled

Drilled = garbage.

A good set of pads with the right compound for your application (be it street or track duty), fresh fluid (DOT4 or better) and a set of steel braided lines will do FAR more to improve your braking and decrease pedal effort than any "bling bling" rotors will ever get you.

 

[McLovin]

Without going into any of the technicalities it comes down to this:

Blanks > *

Slotted > Drilled

Drilled = garbage.

A good set of pads with the right compound for your application (be it street or track duty), fresh fluid (DOT4 or better) and a set of steel braided lines will do FAR more to improve your braking and decrease pedal effort than any "bling bling" rotors will ever get you.

I was reading somewhere that OEM lines are better for DD's because it is easier to tell if the line is bad versus Braided where you can't see anything until it is too late.

I know on a Mustang Forum I frequent one guy was saying that recommended replacement intervals for Braided lines is once every year or two.

 

[phucheneh]

I was reading somewhere that OEM lines are better for DD's because it is easier to tell if the line is bad versus Braided where you can't see anything until it is too late.

I know on a Mustang Forum I frequent one guy was saying that recommended replacement intervals for Braided lines is once every year or two.

You can't evaluate the condition of the rubber with the braided ones. But with modern hoses, it takes a long time before you can just look at them and see cracking/dry rot/ect. Pretty much every hose I've replaced because of external damage has been because of leakage near the fitting...which you'd still see with braided lines. Maybe you'd get a little more warning if you frequently give your hoses a close inspection...but I just don't see that happening with most people.

Otherwise, hoses are more frequently replaced because of internal failure (initial complaint: pulling under braking).

I would not be concerned with braided hoses causing any extra issues. Just IMO, for whatever it's worth to anyone. I also dunno if I believe the claims of big improvements...but if you can competently bleed your brakes, I don't think any bad will come from installing them.

OTOH, drilled/slotted rotors on a street car...worthless. Get stock replacements, a decent set of upgraded 'street' pads, and bed them in properly. Done. You won't look at cool, but you'll brake better.

I installed Stoptech 'Street Performance', I think (whichever ones Rockauto sells), on all four corners for someone a little while ago. I thought it was a massive improvement.

 

[foghorn67]

I would look into a "mild" upgrade. Better pads go a long way. Hawk, Stoptech, EBC are all premium brands.
Rotors, I would just replace with NAPA Premium Gold or EBC.
EBC is made in England and USA.

 

[madoka]

Slotted > Drilled

Drilled = garbage.

Tell that to Brembo, Porsche, BMW M Division, Corvette, Ferrari, etc. They all come standard with cross drilled rotors.

http://www.ebay.com/gds/Drilled-vs-slotted-rotors-what-is-better-/10000000005243690/g.html

As a member of the SAE (Society of Automotive Engineers), I was pleased to see a paper "The Effect of Rotor Crossdrilling on Brake Performance" by two GM engineers published in 2006. They examined three vehicle platforms with cross-drilled rotors vs standard rotors to measure convection cooling capability, fade characteristics, wet braking, pedal feel and lining wear. The result is summarized as follows:

1. For the sports sedan, the coefficient of friction was 21% higher for drilled rotors than standard front rotors at 340F and higher using 15 brake snubs at 62mph. The track simulated 124 mph fade test showed 37% better brake output for drilled rotors. The drilled rotor brake temperature was about 150 degrees cooler.

2. For the performance car, the coefficient of friction was significantly higher for drilled rotors especially at high temperature.

3. Wet braking at high pedal pressure was the same for drilled or standard rotors. Wet braking is not significantly improved by drilled rotors.

4. Pedal force was much more consistent with drilled rotors over the brake temperature range. That is, to stop at the same deceleration rate, the driver does not need to modulate pedal pressure based on different brake temperatures. This reduces driver fatigue and improves brake response.

The authors also reported that drilled rotors prevent pad resin glazing on the rotor. So we now have solid evidence that drilled rotors have benefits over standard rotors. However, I have not found any published paper to show how slots affect brake output. So I reviewed inertial dynamometer tests using ISO NWI 26867 from Link Testing in Detroit with slotted rotors vs standard rotors. The results showed no significant difference in the coefficient of friction during the fade sections, hot stop section or pedal sensitivity portion of the test. My hypothesis is that slotted rotors do not contribute to rotor cooling whereas drilled rotors improve convection heat transfer to cool rotors and reduce brake fade. I should also point out that the pad lining wear for the slotted rotor was very severe during the test, i.e. the pad was chewed up over 20% more than the lining with stock rotors. While I believe that slots will help remove gas and debri from under the pad, I am not sure that this has a significant effect on brake torque for normal street driving. Perhaps the effect of slotted rotors is more significant on the race track, and conversely, I believe that drilled rotors are better for street and highway driving. For most drivers, I recommend drilled rotors over slotted rotors, and this conclusion is supported by the fact that Corvette, Ford GT, Porsche, Mercedes and BMW come with OEM drilled rotors.

 

[trenchfoot]

Tell that to Brembo, Porsche, BMW M Division, Corvette, Ferrari, etc. They all come standard with cross drilled rotors.

http://www.ebay.com/gds/Drilled-vs-slotted-rotors-what-is-better-/10000000005243690/g.html

As a member of the SAE (Society of Automotive Engineers), I was pleased to see a paper "The Effect of Rotor Crossdrilling on Brake Performance" by two GM engineers published in 2006. They examined three vehicle platforms with cross-drilled rotors vs standard rotors to measure convection cooling capability, fade characteristics, wet braking, pedal feel and lining wear. The result is summarized as follows:

1. For the sports sedan, the coefficient of friction was 21% higher for drilled rotors than standard front rotors at 340F and higher using 15 brake snubs at 62mph. The track simulated 124 mph fade test showed 37% better brake output for drilled rotors. The drilled rotor brake temperature was about 150 degrees cooler.

2. For the performance car, the coefficient of friction was significantly higher for drilled rotors especially at high temperature.

3. Wet braking at high pedal pressure was the same for drilled or standard rotors. Wet braking is not significantly improved by drilled rotors.

4. Pedal force was much more consistent with drilled rotors over the brake temperature range. That is, to stop at the same deceleration rate, the driver does not need to modulate pedal pressure based on different brake temperatures. This reduces driver fatigue and improves brake response.

The authors also reported that drilled rotors prevent pad resin glazing on the rotor. So we now have solid evidence that drilled rotors have benefits over standard rotors. However, I have not found any published paper to show how slots affect brake output. So I reviewed inertial dynamometer tests using ISO NWI 26867 from Link Testing in Detroit with slotted rotors vs standard rotors. The results showed no significant difference in the coefficient of friction during the fade sections, hot stop section or pedal sensitivity portion of the test. My hypothesis is that slotted rotors do not contribute to rotor cooling whereas drilled rotors improve convection heat transfer to cool rotors and reduce brake fade. I should also point out that the pad lining wear for the slotted rotor was very severe during the test, i.e. the pad was chewed up over 20% more than the lining with stock rotors. While I believe that slots will help remove gas and debri from under the pad, I am not sure that this has a significant effect on brake torque for normal street driving. Perhaps the effect of slotted rotors is more significant on the race track, and conversely, I believe that drilled rotors are better for street and highway driving. For most drivers, I recommend drilled rotors over slotted rotors, and this conclusion is supported by the fact that Corvette, Ford GT, Porsche, Mercedes and BMW come with OEM drilled rotors.

I'm currently in the process of restoring my '73 Vette and the information you posted is exactly what I needed to know. Thanks much. :thumbsup:

 

[KentState]

Tell that to Brembo, Porsche, BMW M Division, Corvette, Ferrari, etc. They all come standard with cross drilled rotors.

http://www.ebay.com/gds/Drilled-vs-slotted-rotors-what-is-better-/10000000005243690/g.html

As a member of the SAE (Society of Automotive Engineers), I was pleased to see a paper "The Effect of Rotor Crossdrilling on Brake Performance" by two GM engineers published in 2006. They examined three vehicle platforms with cross-drilled rotors vs standard rotors to measure convection cooling capability, fade characteristics, wet braking, pedal feel and lining wear. The result is summarized as follows:

1. For the sports sedan, the coefficient of friction was 21% higher for drilled rotors than standard front rotors at 340F and higher using 15 brake snubs at 62mph. The track simulated 124 mph fade test showed 37% better brake output for drilled rotors. The drilled rotor brake temperature was about 150 degrees cooler.

2. For the performance car, the coefficient of friction was significantly higher for drilled rotors especially at high temperature.

3. Wet braking at high pedal pressure was the same for drilled or standard rotors. Wet braking is not significantly improved by drilled rotors.

4. Pedal force was much more consistent with drilled rotors over the brake temperature range. That is, to stop at the same deceleration rate, the driver does not need to modulate pedal pressure based on different brake temperatures. This reduces driver fatigue and improves brake response.

The authors also reported that drilled rotors prevent pad resin glazing on the rotor. So we now have solid evidence that drilled rotors have benefits over standard rotors. However, I have not found any published paper to show how slots affect brake output. So I reviewed inertial dynamometer tests using ISO NWI 26867 from Link Testing in Detroit with slotted rotors vs standard rotors. The results showed no significant difference in the coefficient of friction during the fade sections, hot stop section or pedal sensitivity portion of the test. My hypothesis is that slotted rotors do not contribute to rotor cooling whereas drilled rotors improve convection heat transfer to cool rotors and reduce brake fade. I should also point out that the pad lining wear for the slotted rotor was very severe during the test, i.e. the pad was chewed up over 20% more than the lining with stock rotors. While I believe that slots will help remove gas and debri from under the pad, I am not sure that this has a significant effect on brake torque for normal street driving. Perhaps the effect of slotted rotors is more significant on the race track, and conversely, I believe that drilled rotors are better for street and highway driving. For most drivers, I recommend drilled rotors over slotted rotors, and this conclusion is supported by the fact that Corvette, Ford GT, Porsche, Mercedes and BMW come with OEM drilled rotors.

Yet, GM ditched cross drilled rotors for the C7 and put blanks on the ZL1 and CTS-V which all came out in 2009 and later. These are all Brembo brakes so I wonder why they ditched their early study results.

 

[JCH13]

Great info Madoka.

Though the concerns that the study raises seem relevant to serious race track conditions, where brake fade and consistency are real concerns. Even then, they're not always concerns. Driving around on the street should be a cake walk for any decent OEM braking system in good repair.

There are plenty of examples of drilled rotors that have prematurely failed (on street cars anyway). I would think that the durability and lower cost of a solid rotor would be better for a street car.

The only time a slotted rotor would be 'worth it' IMO is if braking is unsatisfactory, ABS cannot be tripped in ideal conditions, and larger diameter brakes or larger calipers are not viable options. That is to say, if you can break (brake?) your warm tires loose on dry pavement then you don't need drilled rotors. Noticeable brake fade should never be an issue on the street.

Personal experience:

I have driven a MK2 MR2 in several endurance races, i.e. ~2 hour driving stints at race speed. The race car has good brake fluid, old OEM brake lines, plain OEM rotors, and R4E brake pads. No R-Comp tires, just 200utqg Dunlop Star-specs.

I don't notice any significant brake fade over the course of a driving stint. The car can always lock up over-sized, hot, tires (stock is around 185f/205r, race cars are 195-215f/225-235r widths). Lots of cracks develop in the rotors over the course of 6-10 races, but because there are no holes in the rotors to connect the cracks the rotors have always held up.

My conclusion from this: good brake pads and fresh brake fluid are the best brake upgrades you can make.

I also have my own personal MK2 MR2 with drilled rotors (previous owner installed them). I don't notice any braking advantage from them, during spirited driving or otherwise.

TL;DR

Sure, drilled rotors have some performance advantages over plain rotors. You (meaning the 99.999% of the population that's not a professional race car driver) will probably never notice the performance difference between a plain rotor and a drilled rotor. What you will notice the extra cost and the lower durability.

New OEM brake lines, good rotor blanks, fresh brake fluid, and good brake pads will be all you'll ever need.

 

[EightySix Four]

Yet, GM ditched cross drilled rotors for the C7 and put blanks on the ZL1 and CTS-V which all came out in 2009 and later. These are all Brembo brakes so I wonder why they ditched their early study results.

The study did not cover cracking or increased prices.