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Brake rotor wear, minimum thickness

PostPosted: Mon Aug 05, 2013 10:32 am
by dcgsrider
I have an '09 1200 GS with 55,000 miles on it. I've been noticing a "pulse" in the brake lever during and after my West Coast trip, so I pulled out my micrometer yesterday, and the rotors measured 3.8 and 3.9 mm. There may also be a slight warp or bent in one of the rotors that accounts for the pulse. The pulse is not bad enough to warrant rotor replacement for that alone. BMW spec (stamped on rotor) is 4.0 mm. I have a vague recollection of George mentioning at the Square Root Rally this year that the BMW spec. is conservative. Anyway, just wondering what the consensus is on replacing rotors just a little out of spec. Non-OEM replacements are $400-500.

Re: Brake rotor wear, minimum thickness

PostPosted: Mon Aug 05, 2013 1:44 pm
by biometrics

Like George at BUA, I also believe that the thickness number stamped in the rotors is a conservative one... Before I would replace the rotors I would try removing them and dressing them lightly with a coarse sanding disk... it may be that the rotor surface is actually clogged with brake pad material in varying spots and that is causing the pulse you are experiencing...

Refreshing the rotor surface may give you a few more thousands of miles on those rotors... and if it doesn't work, then you have lost nothing but the time invested... let us know how it goes. If you have a good friend with a machine shop, you might ask him to surface grind a few ten-thousandths off the rotor sides...


Re: Brake rotor wear, minimum thickness

PostPosted: Sun Oct 07, 2018 6:29 pm
by thanatos1224
I be darn,... I did a quick search and found this thread and bam there was the answer I was looking for. THANK YOU

Re: Brake rotor wear, minimum thickness

PostPosted: Thu Jan 17, 2019 8:04 pm
by Max
If they are under stamped value, you are playing with more warping or even lose of brakes due to broken disk. New ones are more durable due to production advancements, Some of them have different cooling holes today. I would advise to change them. Brakes and rubber save lives. DO not machine them or sand them if they are under nominal value. BMW derives those numbers out of years of engineering and tests. If grooves on them are too big, you lose braking surface.