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      09-15-2019, 04:50 PM   #1
David0ff
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Hey Guy
This is my first set of rotors, original, car has 15k Kms and around 5000kms on the track
Pads are HP Plus all corners

I took several shots of my front driver rotor but passenger is the same.

I read somewhere that rotors need to be changed if any of 3 conditions are met:
- cracks link 2 holes (not my case)
- cracks exit rotor surface , in/out ( not yet)
- most of the cracks are longer than 13mm (getting there)

What's the status of these rotors?

Thx
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      09-15-2019, 07:06 PM   #2
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I have been told my rotors have two or three track weekends left.
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      09-15-2019, 09:14 PM   #3
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So when either of you replace your rotors, are you going OEM, aftermarket rotors, or BBK? Try to get replaced under warranty? Curious in that I figured I will have to at some point.
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      09-15-2019, 09:32 PM   #4
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I will go OEM if I am ready to move on from the M4, otherwise I will go with a non OEM slotted rotor.

I usually track a car for a year or two, then I will move on. Presently I love the way my M4 feels.
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      09-15-2019, 10:43 PM   #5
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I will also do either oem or oem equivalent replacement depending on what's available, not looking for BBK right now

Not sure my warranty covers this
2018 M4 lease Canadian Car
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      09-16-2019, 05:11 AM   #6
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These rotors almost look like new . The replacement conditions you specify in your OP are correct as long as you meet the minimum thickness. You are good for way more than 2 more track days .

From the BMW M3 / M4 Brake Systems: Deep Dive and Interview :

Quote:
Why is it that with perforated brake discs in particular, you occasionally see slight cracks?

Cracks form in particular wherever relatively cold discs are suddenly subjected to a large load. The cracks that occur are limited to the surface areas. For instance, if you have been driving your car fully laden on the motorway for an extended period without braking and then you are suddenly called upon to perform an emergency braking manoeuvre, the brake disc will become very hot in a very short space of time – in such a case, the temperature can increase from around 20 degrees to 450 degrees. If the brake disc is required to perform in this manner several times in rapid succession, it is quite possible for surface cracks to form in the cast material of the friction ring – especially in the area around the perforation holes. In sports cars, cracks like these are, more than anything, a sign that they are being subjected to the use for which they were designed, and they have no negative effect on the service life of the brake disc or its braking performance.
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      09-16-2019, 05:24 AM   #7
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What is the thickness of the rotors? Have you measured it? If they are under the minimum thickness, they need replacing.

5000kms of track time is a lot! Are you sure it is that much? If that is truly the case, I would be amazed if the original rotors were still ok.
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      09-16-2019, 08:06 AM   #8
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Quote:
Originally Posted by CanAutM3 View Post
These rotors almost look like new . The replacement conditions you specify in your OP are correct as long as you meet the minimum thickness. You are good for way more than 2 more track days .

From the BMW M3 / M4 Brake Systems: Deep Dive and Interview :

Quote:
Why is it that with perforated brake discs in particular, you occasionally see slight cracks?

Cracks form in particular wherever relatively cold discs are suddenly subjected to a large load. The cracks that occur are limited to the surface areas. For instance, if you have been driving your car fully laden on the motorway for an extended period without braking and then you are suddenly called upon to perform an emergency braking manoeuvre, the brake disc will become very hot in a very short space of time – in such a case, the temperature can increase from around 20 degrees to 450 degrees. If the brake disc is required to perform in this manner several times in rapid succession, it is quite possible for surface cracks to form in the cast material of the friction ring – especially in the area around the perforation holes. In sports cars, cracks like these are, more than anything, a sign that they are being subjected to the use for which they were designed, and they have no negative effect on the service life of the brake disc or its braking performance.
Awesome thank you

When's the next tremblant?
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      09-16-2019, 08:12 AM   #9
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Quote:
Originally Posted by robbo mcs View Post
What is the thickness of the rotors? Have you measured it? If they are under the minimum thickness, they need replacing.

5000kms of track time is a lot! Are you sure it is that much? If that is truly the case, I would be amazed if the original rotors were still ok.
I will measure it but it's well above min,
Also I don't run my pads much below 40% so min thickness is not something I'm concerned about. As I understand it min thickness is something to worry about if you have rotor at min thick and Pads worn to the plate then you risk having your piston fall off.

I think cracks will kill mine before min thickness achievement unlock.

Also the local tracks I go to are not that high speed, max deceleration is 165kmh -> ~80

But I do go a lot haha and do around 100-120 kms a day, I go ~2-3 times a week

I will check min and update
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      09-16-2019, 11:33 AM   #10
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You may want to consider DIY brake ducts for the next set of rotors.

When my rotors got to that point I started looking at them after every session just in case. However, I've seen plenty of older Porsche's run them until there's hundreds of cracks across the rotor face.
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      09-16-2019, 06:45 PM   #11
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Quote:
Originally Posted by OhioRiderAaron View Post
You may want to consider DIY brake ducts for the next set of rotors.

When my rotors got to that point I started looking at them after every session just in case. However, I've seen plenty of older Porsche's run them until there's hundreds of cracks across the rotor face.
I'd love to put some brake ducts in, but where are people running the hoses? I haven't found a good location.
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      09-16-2019, 07:15 PM   #12
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Quote:
Originally Posted by David0ff View Post
Awesome thank you

When's the next tremblant?
September 25th. Last day of the season
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      09-16-2019, 09:03 PM   #13
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Originally Posted by CanAutM3 View Post
September 25th. Last day of the season
Lots of Canadians buying or renting winter homes here in Phoenix Our season is just starting to ramp up.
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      09-16-2019, 09:08 PM   #14
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Lots of Canadians buying or renting winter homes here in Phoenix Our season is just starting to ramp up.
I can't complain though, I've had a pretty decent season this year with 24 track days
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      09-17-2019, 06:18 PM   #15
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I can't complain though, I've had a pretty decent decent season this year with 24 track days
way to max out the short northeast season.
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      09-25-2019, 09:01 PM   #16
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I added 3 days at COTA last weekend, about 5-1/2 track hours.
These Beaches are still holding on.
This is with PFC08 pads.

46k total miles on the rotors.
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      09-25-2019, 10:02 PM   #17
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Quote:
Originally Posted by Suds View Post
I added 3 days at COTA last weekend, about 5-1/2 track hours.
These Beaches are still holding on.
This is with PFC08 pads.

46k total miles on the rotors.
Looking good!

So I got around measuring mine when changing pads/fluid this weekend
Both fronts are above 30mm thick so I guess they still have some life left
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      09-25-2019, 10:17 PM   #18
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We all prefer to stay on the conservative side of oh shit!
We spend good money on track time and we don’t want to go home early with broke stuff.
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      09-26-2019, 11:25 PM   #19
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I heard until a crack around a hole extends all the way to outer or inner edge they are good to use. I learned from experience that it's not a good idea to run it till it gets too thin which caused excessive pad wear due to too much heat.

I've just got these two piece rotors after waiting 3 weeks and blowing up the whole last month of the season.
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      09-27-2019, 12:27 AM   #20
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Quote:
Originally Posted by MyFragileHalogen View Post
I heard until a crack around a hole extends all the way to outer or inner edge they are good to use. I learned from experience that it's not a good idea to run it till it gets too thin which caused excessive pad wear due to too much heat.

I've just got these two piece rotors after waiting 3 weeks and blowing up the whole last month of the season.
What rotors are those?
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      09-27-2019, 01:15 AM   #21
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Quote:
Originally Posted by David0ff View Post
What rotors are those?
made by a company called racingbrake; they claim that their design has best of both world in slotted + drilled for track use. OEM rotors shipped box was 55lbs which I returned. These were 45lb in the shipped box.
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      09-27-2019, 08:26 AM   #22
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Quote:
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Quote:
Originally Posted by David0ff View Post
What rotors are those?
made by a company called racingbrake; they claim that their design has best of both world in slotted + drilled for track use. OEM rotors shipped box was 55lbs which I returned. These were 45lb in the shipped box.
Thx!

Curious to see how they hold up and perform in the heat of battle
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