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      09-16-2019, 05:11 AM   #6
Lieutenant General
CanAutM3's Avatar

Drives: 2019 M4cs
Join Date: Jan 2012
Location: Montreal

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Garage List
2019 BMW M4cs  [0.00]
2018 Audi RS3  [0.00]
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 :

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.
///M4cs 2019 F82 Lime Rock Grey
MPE / CF Mirror caps / MP-HAS / GC Camber plates

Last edited by CanAutM3; 09-16-2019 at 07:30 AM..