Quote:
Originally Posted by brad850csi
Pads are measured by their thickness. As they provide a heatsink to the discs you don't want to get them too low as that will accelerate the wear of the discs.
The discs are measured by weight, not thickness. Each disc will have a minimum weight printed on it.
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To expand on Brad's comment here....
Pads are just one wear item and the computer indicator from the brake pad sensor is an estimate. A very good estimate based on my decades of BMW ownership, but still an estimate.
Your brakes likely will need changing based on those indicators.
To answer your question, dealers check the computer, and they perform a pad thickness measurement.
Now rotors is a whole different story. CCB rotors need to be weighed. You should not balk at the cost associated with dismounting each rotor to weigh them, but considering a whole set is $10,000, it's little money spent to gauge how much more life you have left. CCB's have relatively huge variability in manufactured weight, which means each rotor begins in life with a different weight. Also the precision involved in measuring the weight is very minute. So each one technically should be cleaned before weighing.
There is a visual indicator for rough estimate on the rotors. They are little dime sized circles etched into the rotor. When those circles become non-circles, that indicates the rotors wearing down towards the end of life.
The only way that I'm aware of that that you can measure rotor weight without taking the rotor off is with the carboteq tool.
https://www.proceq.com/product/carbo...c-brake-discs/
Most independent Porsche shops should have these laying around. You should take your car to these shops and pay them for a half hour of their time for using their tool. If you feel like your trajectory of ownership will be owning CCB equipped cars, you can probably just buy the tool out right. Pretty much all modern day exotics, and many mid tier Porsche models come with CCBs. Save you a lot of money over time.
Google BMW CCB rotor wear indicator and you'll see a BMW manual out there that shows you what to look for on the rotor. It's also in the video I posted above. There's still a minimum rotor thickness measure, but it's a high precision measurement, that requires calibrated tools.
Lastly there's a theory out there among CCB owners across all manufacturers that you should change your pads halfway through their life anyways. It somehow extends the longevity of your rotors. Don't ask me why, I haven't had time to pour through the forums discussing this topic and rationale.