Should I worry about the small cracks on the brake rotor?

[shaftwhy]

So of course the small cracks start to show on the brake rotors. How long do I still have for those rotors?

If I need to replace them, can I just replace the front ones at first, since the rear ones are still no showing any crack yet?

[Racing Instructor]

Originally Posted by shaftwhy

So of course the small cracks start to show on the brake rotors. How long do I still have for those rotors?

If I need to replace them, can I just replace the front ones at first, since the rear ones are still no showing any crack yet?

Short answer: yes. However, small cracks like that are not an issue. They are surface cracks and normal. The thing to watch is the thickness of the rotor. I think that if they need to be replaced it may be covered under your warranty. BMW just replaced all the brakes on my car under the warranty/maintenance.

Here is a video featuring Klaus Dullinger who designed the M3/M4 brakes.

http://www.bmwblog.com/2014/04/13/ne...-brake-system/

[shaftwhy]

Originally Posted by Racing Instructor

Short answer: yes. However, small cracks like that are not an issue. They are surface cracks and normal. The thing to watch is the thickness of the rotor. I think that if they need to be replaced it may be covered under your warranty. BMW just replaced all the brakes on my car under the warranty/maintenance.

Here is a video featuring Klaus Dullinger who designed the M3/M4 brakes.

http://www.bmwblog.com/2014/04/13/ne...-brake-system/

Thanks, will mention this to my SA at next service. I am not sure if they will cover though, because 1.5 year ago they already did one time courtesy replacement for my rotor, which is totally unnecessarily because of uneven pad deposit.

[OhioRiderAaron]

Plenty of life left in those. Keep on driving and enjoying em

When you get to a point of replacement (again you're not close yet) I'd recommend replacing in pairs, that way everything is on a similar replacement schedule. No need to replace the rears until the min. thickness is reached or the cracking is extreme (which is going to take a longgg time). I'm on my 2nd set of front rotors, original rears, no issues.

[shaftwhy]

Originally Posted by OhioRiderAaron

Plenty of life left in those. Keep on driving and enjoying em

When you get to a point of replacement (again you're not close yet) I'd recommend replacing in pairs, that way everything is on a similar replacement schedule. No need to replace the rears until the min. thickness is reached or the cracking is extreme (which is going to take a longgg time). I'm on my 2nd set of front rotors, original rears, no issues.

Thanks! How do I tell whether it is too thin?

[CanAutM3]

That's nothing. Cracking is normal. From the brake system 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. When it is time to change the brake pad, it is also necessary for the car dealer to inspect the brake disc.

Even with cracks that look pretty bad, the rotors can still be fine. However, you should replace the rotors as soon as you have cracks that connect two crossdrill holes together or even more urgently (read replace immediately), when there is a crack that reaches the outer edge of the rotor.

[Racing Instructor]

Originally Posted by shaftwhy

Thanks! How do I tell whether it is too thin?

There is a minimum thickness etched on the rotors and I think it is 28.4 MM.

[mcvaughan]

Small cracks are normal.