Cracked cross drilled rotor
11-26-2000, 10:27 PM
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Just found this pic out when I was organizing my photos from various track days that I had this year.
Let's hope the image link works in ubb. This does not look pretty. That is why I really hate crossed drilled rotors. They look cool and they work great at the track. but, at the expense of short life time and high dollar. I first discovered them at the Michigan International Speedway. Man, approaching turn 1 at 145MPH down to 40 something (Forgot how low, all I remember I was on 2nd gear) with cracked rotors wasn't cool.
I remember awhile ago someone was discussing about cross drill rotors. I just want to share it with the people on the board.
Let's hope the image link works in ubb. This does not look pretty. That is why I really hate crossed drilled rotors. They look cool and they work great at the track. but, at the expense of short life time and high dollar. I first discovered them at the Michigan International Speedway. Man, approaching turn 1 at 145MPH down to 40 something (Forgot how low, all I remember I was on 2nd gear) with cracked rotors wasn't cool.
I remember awhile ago someone was discussing about cross drill rotors. I just want to share it with the people on the board.
11-27-2000, 03:53 AM
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I much prefer gas slotting over cross drilling if you are going to alter the disc surface. Drilling fell out of favor in racing around 15 years ago and is now basically used only when you have to (stock rules) or need a lighter disc on a low braking track. The holes form what is known as stress risers so the cracking is no surprise. The most crack resistant "drilled" discs are the kind where the hols are cast in and the disc itself is heavier than normal which reduces the cracking issue. BTW curved vane discs were invented to deal with cracking problems sice a crack will stop when it hits the thick web section. One thing drilling does is cut weight - often 1-2 pounds. This leads to less mass to absorb all of the energy so it can run hotter during the stop process. For example if you have a 15 pound disc and drill it winding up with 1.5 pounds less weight you will increase the temperature rise during braking around 10%. Gas slotting cuts around 2 ounces of mass which is negligible. Slotting or drilling is much less necessary when you use the high tech carbon pads some of which are so fade resistant. When used with normal pads, drilling or slotting helps initial brake torque response and provides more brake torque during pad fade periods since the dust and gas is vented and wiped away. This mechanical wiping effect can wear the pads more during the pad fade period but then again you are enjoying increased brake power too. Extra pad wear is basically negligible during regular braking. Even with carbon pads, intial bite or response is sometimes improved with slotted or drilled discs, especially slotted.
Stan
Stan
11-27-2000, 05:14 AM
#4
Cross-drilled rotors do basically nothing to improve performance on the street and are overated for the track !
Quality pads(Hawk,Porterfield,etc.) contribute much more to braking efficiency than cross-drilled or slotted rotors ever will, but since they are not sexy.....
Pierre
Quality pads(Hawk,Porterfield,etc.) contribute much more to braking efficiency than cross-drilled or slotted rotors ever will, but since they are not sexy.....
Pierre
11-27-2000, 05:36 AM
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<<Yes. Sort of. This is somewhat overshadowed by the increased surface area and venting provided by the drilled rotors. BTW, going from solid to drilled on my S2000 took off 7 ounces at the front and 3 at the rear. Different disks thou (curved vanes, etc...)>>
Drilled discs have reduced effective swept area. The induced airflow on a vented disc is from the small radius toward the large radius. Centrifugal. That is the air goes in the back of the disc where the disc vents begin and then exits out the disc outside diameter. There is lttle airflow through the holes of a drilled disc compared to the vents. The holes would actually work better if they were angled!!! The holes are major stress concentration zones and almost always crack to some extent when used hard. Sometimes discs fy apart which then hard-locks that wheel and a crash usually results. Drilled discs look HOT though. Porsche casts in the holes and oversizes the discs and often uses curved vane discs so their disc holes are much less prone to cracking. If your discs work better than stock on the track is is more likely that this is due to mechanical edge effects (which slotting can provide without reducing your heat sink mass and increasing the risk of cracking.) rather than cooling improvement. If you want significant cooling improvement then you need lots of cooling air brought to the disc in such a way that both sides are equally and adequately cooled.
You can get curved vane discs for S2Ks but they appear to have a major flaw. They need to be made in left and right orientations but they appear to be only left or right. This means that one side of the car will have much reduced induced airflow throught that disc. It might actually be cheaper to have true racing rotors made instead of buying the catlaog discs.
<<One of the main disadvantages of slotted rotors is that their effectiveness lowers as they wear. This, obvioulsy, does not apply to drilled rotors. >>
I don't know where you heard that - it's a total nonissue on properly slotted discs!!
The slots are normally cut to a depth somewhat less deep than the disc wear limit. For example on BMWs the wear limit is often about 0.030 inches thickness per side and the slots are typically about 0.020-0.025 deep. You can tell when your discs are too thin by the slots being erased. Note that they don't "erase" evenly on a given side or even side to side. There are always areas that wear before others. So you have some warning. Cars with calipers like the S2ks (floaters)generally wear the back side slightly faster than the front side due to slightly uneven side to side pressure. The slots don't have to be deep to work, as the hot gas and dust can escape easily. For the best track braking and coolest running brakes you want as close to full disc thickness as this is your heat sink and the temp rise is proportional to the mass. Heavy discs and lots of cooling are your friends if you are running tto hot.
Take a look at the "brake-cams" for televised stock car events at Martinsville. That track is an oval with two dragstrips connected by two hairpin turns. Two laps (about 40 seconds) into a race the disc are yellow hot. Noone. I mean noone uses drilled discs there. Nearly all the cars use Performnance Friction carbon metallic pads, even the "Raybestos Brakes" team, a brake pad competitor. Discs are either plain or slotted and they use multiple cooling ducts with a large one sealed to the eye of the disc and no splash shields. The compounds they use are race only and have about 55-60% iron content. They wear well under those conditions but eat rotors under low braking conditions such as street use.
Stan
Drilled discs have reduced effective swept area. The induced airflow on a vented disc is from the small radius toward the large radius. Centrifugal. That is the air goes in the back of the disc where the disc vents begin and then exits out the disc outside diameter. There is lttle airflow through the holes of a drilled disc compared to the vents. The holes would actually work better if they were angled!!! The holes are major stress concentration zones and almost always crack to some extent when used hard. Sometimes discs fy apart which then hard-locks that wheel and a crash usually results. Drilled discs look HOT though. Porsche casts in the holes and oversizes the discs and often uses curved vane discs so their disc holes are much less prone to cracking. If your discs work better than stock on the track is is more likely that this is due to mechanical edge effects (which slotting can provide without reducing your heat sink mass and increasing the risk of cracking.) rather than cooling improvement. If you want significant cooling improvement then you need lots of cooling air brought to the disc in such a way that both sides are equally and adequately cooled.
You can get curved vane discs for S2Ks but they appear to have a major flaw. They need to be made in left and right orientations but they appear to be only left or right. This means that one side of the car will have much reduced induced airflow throught that disc. It might actually be cheaper to have true racing rotors made instead of buying the catlaog discs.
<<One of the main disadvantages of slotted rotors is that their effectiveness lowers as they wear. This, obvioulsy, does not apply to drilled rotors. >>
I don't know where you heard that - it's a total nonissue on properly slotted discs!!
The slots are normally cut to a depth somewhat less deep than the disc wear limit. For example on BMWs the wear limit is often about 0.030 inches thickness per side and the slots are typically about 0.020-0.025 deep. You can tell when your discs are too thin by the slots being erased. Note that they don't "erase" evenly on a given side or even side to side. There are always areas that wear before others. So you have some warning. Cars with calipers like the S2ks (floaters)generally wear the back side slightly faster than the front side due to slightly uneven side to side pressure. The slots don't have to be deep to work, as the hot gas and dust can escape easily. For the best track braking and coolest running brakes you want as close to full disc thickness as this is your heat sink and the temp rise is proportional to the mass. Heavy discs and lots of cooling are your friends if you are running tto hot.
Take a look at the "brake-cams" for televised stock car events at Martinsville. That track is an oval with two dragstrips connected by two hairpin turns. Two laps (about 40 seconds) into a race the disc are yellow hot. Noone. I mean noone uses drilled discs there. Nearly all the cars use Performnance Friction carbon metallic pads, even the "Raybestos Brakes" team, a brake pad competitor. Discs are either plain or slotted and they use multiple cooling ducts with a large one sealed to the eye of the disc and no splash shields. The compounds they use are race only and have about 55-60% iron content. They wear well under those conditions but eat rotors under low braking conditions such as street use.
Stan
11-27-2000, 05:48 AM
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<<Cross-drilled rotors do basically nothing to improve performance on the street and are overated for the track ! Quality pads(Hawk,Porterfield,etc.) contribute much more to braking efficiency than cross-drilled or slotted rotors ever will, but since they are not sexy.....>>
YESSSS!!!!!!
In my accelerometer tests I have seen about a 10% improvement in stopping power from slotting alone. You can easily gain 50% from pads, but you gotta be able to deal with the heat and other issues.
One thing that slotted or drilled discs do do that is nice is slightly increase the instant on characteristic of good brakes. But this is much improved anyway with good pads.
After many many years of working on this stuff my conclusion for stock type cars is:
Use high tech pads (must personally try different pads out as there are many factors you may like or dislike - lots of love/hate things here!!!), use good lines, improve cooling and slot the discs before even considering big brakes. Keep records of pad life and temps if possible, pad fade and pad wear go hand in hand - if you have problems with one you have the other too! If you can cut fade significantly, you will seem to "speed up" near the end of a run whereas everyone else is really losing lap time. If possible go up one size in the master cylinder and brace the firewall if possible to cut flex. BTW Sport Compact car found that the extra rotating inertia of big discs on a civic dropped at the wheels HP by about 2.
Stan
YESSSS!!!!!!
In my accelerometer tests I have seen about a 10% improvement in stopping power from slotting alone. You can easily gain 50% from pads, but you gotta be able to deal with the heat and other issues.
One thing that slotted or drilled discs do do that is nice is slightly increase the instant on characteristic of good brakes. But this is much improved anyway with good pads.
After many many years of working on this stuff my conclusion for stock type cars is:
Use high tech pads (must personally try different pads out as there are many factors you may like or dislike - lots of love/hate things here!!!), use good lines, improve cooling and slot the discs before even considering big brakes. Keep records of pad life and temps if possible, pad fade and pad wear go hand in hand - if you have problems with one you have the other too! If you can cut fade significantly, you will seem to "speed up" near the end of a run whereas everyone else is really losing lap time. If possible go up one size in the master cylinder and brace the firewall if possible to cut flex. BTW Sport Compact car found that the extra rotating inertia of big discs on a civic dropped at the wheels HP by about 2.
Stan
11-27-2000, 10:35 AM
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[QUOTE]Originally posted by E30M3:
[B]
You can get curved vane discs for S2Ks but they appear to have a major flaw. They need to be made in left and right orientations but they appear to be only left or right.
[B]
You can get curved vane discs for S2Ks but they appear to have a major flaw. They need to be made in left and right orientations but they appear to be only left or right.
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11-27-2000, 11:19 AM
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RE curved van rotors. <<ummm. We discussed this before and the consensus was that it didn't make a difference. I will watch out as my rotors wear and will let you know. >>
Luis, consensus may be that it is fine. But in this case it is just plain wrong. Both are facts.
I have personally measured induced airflow on many different rotors. Including many curved van rotors ranging from ZR-1, Supra, M3 floating, Indy car and Nascar , etc, etc. All of them are handed (L/R) and all move more air when mounted properly on the side of the car for which they were designed. One of your discs is not getting as much induced air flow as the other. This is probably not that bad for street use. I don't know how much those cost but indy car discs without hats run around 100-400 bucks apiece, more for the fanciest versions.
<<Doesn't make sense to me. If the slots are less deep than the wear limit one of two things will happen: You either get rid of your rotors well before they get to their wear limit or you end up with no slots at all(ok, some slots, assuming wear is not uniform). What am I missing?>>
Just reread my post. Rotors used hard don't wear perfectly. Certain radii will "go" before others. They can come fairly close to super even wear if they are used gently and with mild pads. Often discs that are used hard get some grooving which is not a big deal. And near the edges of the pad near the OD and ID of the rubbing area wears less. My M3 wears the front discs the most at about 1/3 of the way out from the inner rub radius and more on the inside than the outside surface.
<<You raise excellent points and obviously know what you're talking about, but I'd say that some of your comments apply mainly to people that are trying to shave the last nanosecond that will get them to motordomhood.
>>
Hey I'm a hard core guy and have been so for a long time!!! I've helped many nuts go faster over the years.
<< Porsche and other top of the range sports cars have been shipping drilled rotors for as long as I can remember. I'm sure looks plays a major part, but then again very little people here are professional racers and these things do matter (if you don't believe, ask how many would install the ugly but functionally effective Mugen aero parts). As a datapoint, they matter to me. >>
Drilled rotors look hot. So do dual exhausts on 4 cylinder cars. Huge yet heavy wheels can look great but can slow you down. Marketing. Rice. REAL racers don't use stuff that doen't work cuz then you lose.
Stan
Luis, consensus may be that it is fine. But in this case it is just plain wrong. Both are facts.
I have personally measured induced airflow on many different rotors. Including many curved van rotors ranging from ZR-1, Supra, M3 floating, Indy car and Nascar , etc, etc. All of them are handed (L/R) and all move more air when mounted properly on the side of the car for which they were designed. One of your discs is not getting as much induced air flow as the other. This is probably not that bad for street use. I don't know how much those cost but indy car discs without hats run around 100-400 bucks apiece, more for the fanciest versions.
<<Doesn't make sense to me. If the slots are less deep than the wear limit one of two things will happen: You either get rid of your rotors well before they get to their wear limit or you end up with no slots at all(ok, some slots, assuming wear is not uniform). What am I missing?>>
Just reread my post. Rotors used hard don't wear perfectly. Certain radii will "go" before others. They can come fairly close to super even wear if they are used gently and with mild pads. Often discs that are used hard get some grooving which is not a big deal. And near the edges of the pad near the OD and ID of the rubbing area wears less. My M3 wears the front discs the most at about 1/3 of the way out from the inner rub radius and more on the inside than the outside surface.
<<You raise excellent points and obviously know what you're talking about, but I'd say that some of your comments apply mainly to people that are trying to shave the last nanosecond that will get them to motordomhood.
>>
Hey I'm a hard core guy and have been so for a long time!!! I've helped many nuts go faster over the years.
<< Porsche and other top of the range sports cars have been shipping drilled rotors for as long as I can remember. I'm sure looks plays a major part, but then again very little people here are professional racers and these things do matter (if you don't believe, ask how many would install the ugly but functionally effective Mugen aero parts). As a datapoint, they matter to me. >>
Drilled rotors look hot. So do dual exhausts on 4 cylinder cars. Huge yet heavy wheels can look great but can slow you down. Marketing. Rice. REAL racers don't use stuff that doen't work cuz then you lose.
Stan
11-27-2000, 01:02 PM
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[QUOTE]Originally posted by E30M3:
[B]RE curved van rotors. <<ummm. We discussed this before and the consensus was that it didn't make a difference. I will watch out as my rotors wear and will let you know. >>
Luis, consensus may be that it is fine.
[B]RE curved van rotors. <<ummm. We discussed this before and the consensus was that it didn't make a difference. I will watch out as my rotors wear and will let you know. >>
Luis, consensus may be that it is fine.
11-27-2000, 01:12 PM
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The grooves on the disk are caused by Hawk Blue pads. Now, I am using PF90 and they doesn't not have this grooves. These disks are on my BMW with AP Racing Caliper. 13.3inch diameter floating rotor.
The reason inside of the disk wear out more is because of the temporature. The temporature on the inside is much higher. Theoratically, the caliper should exert the same amount of force on both side of the disk. The only factor that the temp is different on the outside and inside. The same goes to inside brake pad is wearing faster than outside.
Now, I like the solution provided by King Motorsports. I have personally witnessed it on Nick's (GTRPower) S2000. He have recommanded me doing that. So, I guess that will be my next step.
The reason inside of the disk wear out more is because of the temporature. The temporature on the inside is much higher. Theoratically, the caliper should exert the same amount of force on both side of the disk. The only factor that the temp is different on the outside and inside. The same goes to inside brake pad is wearing faster than outside.
Now, I like the solution provided by King Motorsports. I have personally witnessed it on Nick's (GTRPower) S2000. He have recommanded me doing that. So, I guess that will be my next step.