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Replacement Rotors

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AF-MKVI

Go Kart Champion
Sorry, thought you would know plac.


Sonny@TireRack.com said:
Late to the party, sorry. In regards to slotted or drilled rotors: The function of a rotor is basically to act as a heat sink. When you remove material from a rotor (i.e. slots or holes) you limit the ability of a rotor to dissipate heat. Some do tout the benefits of slotted rotors cleaning the pads or assisting when a pad out-gasses. However, in my opinion, less is not more when it comes to braking. That being said....they look awesome :)
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So Sonny, same question. Why do all the OEM's go with drilled rotors on all their high performance car's then?
 
A

AF-MKVI

Go Kart Champion
plac said:
power is my wheelhouse. i know very little about suspension/chassis/brakes really..
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No worries :) Just an honest question, seems to be on one side of the camp are the go with plain rotors only guys or you are a poser and the other side is drilling and slotting is the greatest thing since sliced bread. Surprised with all the great testing tire rack does they have not done any testing of these upgrades. Would love to have a conclusive answer backed up by science here and not opinions.
 
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plac

Guest
ah my slotted rotors work fine. not neccessarily better than stockers from what i have felt.. the pads make a lot more difference than any rotor.. but they look good, so i like them. it doesn't brake *worse* either...
 
A

AF-MKVI

Go Kart Champion
Found my own answer... with science :) yay.

SAE Technical Paper 2006-01-0691

Synopsis

http://www.tazcobra.com/SAE_2006010691_Synopsis.pdf

Conclusion, drilled is better than plain. Drilled and slotted is suggested for best performance and out performs blanks in almost all areas. Only downside noted is increased pad wear by 20-30% on the street and up to 50% faster on the track.
 
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Gunkata

Gunkata

Drag Race Newbie
I've always heard drilled cracks easier than anything else... and most do not track with drilled, yet many OEM MFG's put them on cars because of the "look".
 
A_Bowers

A_Bowers

Moderator
GunKata said:
I've always heard drilled cracks easier than anything else... and most do not track with drilled, yet many OEM MFG's put them on cars because of the "look".
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This.

Never had drilled rotors. Slotted or solid disk. Of you get a good quality rotor, with pads and lines and fluid, no reason why you should need anything else.
 
D

DarkCloak

Banned
GunKata said:
I've always heard drilled cracks easier than anything else... and most do not track with drilled, yet many OEM MFG's put them on cars because of the "look".
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Incorrect. I see a large amount of drilled discs on Race cars and track cars. That is only with Iron however. Indy and F1 cars have switched to carbon and thus have removed the drilled holes. Plus Open wheels cars obviously have 0 issues with receiving adequate airflow to the brakes.

Despite popular belief gasses are still produced by modern brake pads particularly in the rain. However this is due to the semi-metallic pads interacting specifically with Iron. This is more common on the higher performance street and track pads that most of us use that intend to go to a track. Thus with the development of C rotors they have now become obsolete.

As to the comment earlier that no professional racers use slots. NASCAR use them extensively. See photo below:


The most interesting rotor design now is the wave rotor. The RS5 is using this design on Iron rotors. If you opt for the Carbon though they disappear.
 

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Gunkata

Gunkata

Drag Race Newbie
thanks^ i'm assuming people meant with the common compounds we see from the aftermarket or? otherwise, yeah, that must be a huge misconception then.

I recently drove the RS5 and did see the awesome wave rotors.. pretty wild.
 
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DarkCloak

Banned
I saw them for the first time this weekend at Coronado Speed Fest. I was immediatly lured into the brakes. I got to speak to the Audi Rep. This guy was not an engineer though and probably reading from some sales brochure. The waves allow for additional heat to escape by allowing them to rise up and then be swept away as the disc spins. I have not done any independent research into the subject so I can not comment on the validity of these claims
 
Sonny@TireRack.com

Sonny@TireRack.com

sonny@tirerack.com
AF-MKVI said:
Sorry, thought you would know plac.





So Sonny, same question. Why do all the OEM's go with drilled rotors on all their high performance car's then?
Click to expand...

Definitely not claiming to be an automotive engineer, simply an enthusiast...a trained enthusiast, but an enthusiast nonetheless. I would surmise it has to do with some amount of weight savings and simple aesthetics (believe it or not, manufacturers are concerned with looks too :)) Additionally, as already stated, drilled rotors specifically are more susceptible to cracking, especially during track usage...which is why most companies will specifically note that their drilled rotors are not for track use.
 
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D

DarkCloak

Banned
DarkCloak said:
Incorrect. I see a large amount of drilled discs on Race cars and track cars. That is only with Iron however. Indy and F1 cars have switched to carbon and thus have removed the drilled holes. Plus Open wheels cars obviously have 0 issues with receiving adequate airflow to the brakes.

Despite popular belief gasses are still produced by modern brake pads particularly in the rain. However this is due to the semi-metallic pads interacting specifically with Iron. This is more common on the higher performance street and track pads that most of us use that intend to go to a track. Thus with the development of C rotors they have now become obsolete.

As to the comment earlier that no professional racers use slots. NASCAR use them extensively. See photo below:


The most interesting rotor design now is the wave rotor. The RS5 is using this design on Iron rotors. If you opt for the Carbon though they disappear.
Click to expand...

I do have to follow up though that i have only observed slotted discs on oval racers and have never seen one on a professional road circuit car. My guess is that because the oval racer has essential 2-3 non-full stops, enough to maintain momentum around the banking, that the slots keep a fresh surface on the pad since the pads rarely approach lockup on an oval. One could assume that the pads do not get sufficiently grinded down the way they would on a road circuit where a vehicle may break 10-20 per lap. Thus slotting makes a lot of sense on the oval. NASCAR teams actually use different brakes for road and oval circuits. The road circuits are much bigger! Just a little food for thought but that is my guess for their choice.
 
Gunkata

Gunkata

Drag Race Newbie
Sonny@TireRack.com said:
Definitely not claiming to be an automotive engineer, simply an enthusiast...a trained enthusiast, but an enthusiast nonetheless. I would surmise it has to do with some amount of weight savings and simple aesthetics (believe it or not, manufacturers are concerned with looks too :)) Additionally, as already stated, drilled rotors specifically are more suspect to cracking, especially during track usage...which is why most companies will specifically note that their drilled rotors are not for track use.
Click to expand...

Thats what I've always heard^, so who is right?!?! :iono::lol:
 
D

DarkCloak

Banned
A bit of a parallel argument but I like a dedicated set of pads and discs just for the track. That way you can trash them and then change them out before you go home. If you are changing the pads why not do the discs as well?

I have used cross drilled discs for years with no issues. I have however warped a solid discs. That is something not yet raised is that although cross drilled discs are more prone to cracking they are less prone to warping.
 
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AF-MKVI

Go Kart Champion
DarkCloak said:
A bit of a parallel argument but I like a dedicated set of pads and discs just for the track. That way you can trash them and then change them out before you go home. If you are changing the pads why not do the discs as well?

I have used cross drilled discs for years with no issues. I have however warped a solid discs. That is something not yet raised is that although cross drilled discs are more prone to cracking they are less prone to warping.
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The Full SAE paper observed the drilled diisks were over 150 deg. cooler on stops from 99 mph, also they had more even heat transfer across the rotor surface.

I have had drilled rotors crack on me before, but only cheaper ones and a set of factory rotors cracked on my old 999s during a track day. Have not had any problems since.
 
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