modernyankee

Here's the list of charges for when I had mine measured. You'll note that for the purposes of gathering data, I spend more than I needed to by having the technician measure the rotors ON the car, OFF the car and OFF the car with a second Carboteq tool. Yes, he only had to pull the rotors off and put them back on once per corner, but he still had to take 3 measurements at 4 corners and record them, then do that 2 extra times. That must add up to some appreciable time...an hour? two?. Bottom line is that it's not cheap. Best bet is to do this work while you're having your brake pads changed b/c you'll already be paying for most of the removal/reinstallation labor anyway AS WELL AS the nearly $200 worth of bolts they replace every time the brake calipers come off. Those bolts aren't made with magic or fairy dust so why do THOSE bolts cost $31 each but other (very simiilar bolts) cost a couple of dollars each?! Hmmm? I'm sure I'm going to get lambasted for this, but those '1-time use' bolts?...well, I use them 2-3 times b/c I change them 3-4 times per year and the torque spec is so low (63 lb/ft) that I think they don't really twist much (if at all). I'm sure I don't understand why they're single use only and I'd love it if someone could explain why. I assume it's b/c it would be easy to damage the aluminum they screw into if the bolt were re-used many times and became dirty while on the ground and then the dirt would ruin the softer aluminum threads. I clean the bolt and re-use it. I'll swap out the bolts for new ones once per season. Anyway, I hope that answers your question.

DR.S

All this (not equal) measurement values are really confusing from technical POV.

What are the measuring device uncertainties?
How will the values differ if a measurement would be repeated three time without changing anything between?

modernyankee

I agree that while the methods are scientific and tools used are very expensive pieces of precision machinery, the variances don't instill confidence in the results. Interestingly, unlike steel rotors which physically become smaller through use (abrasion), PCCB's stay the same size, but become lighter. If I understand the laws of physics correctly, that means they become less dense through use....which seems to make sense b/c they're giving up carbon. Ultimately, (and in retrospect) I missed the perfect opportunity to WEIGH the rotors...which is actually how one determines when they've 'given up' enough of the carbon that they're no longer suitable for use.
I'll be sure to do that this winter when I have the rotor's measured with the Carboteq tool.
I've read that running the pads below 50% somehow uses up the rotor 'life" (aka carbon content) at a faster rate than if only the first 50% were used. Even if that were true, at $1600 for pads at all 4 corners, I can't see throwing away $800 worth of pads 3x per year to minimize a theoretical incremental increase in rotor wear rate.
Bottom line: I don't know the answers to your questions b/c I haven't done multiple measurements in the same location with the same tool. I will, however, weigh the rotors this winter and will publish the results.

DR.S

My questions weren't up to you specifically but more in general.
I agree, for the cost of the measuring device the results are really "strange".

I also agree not to throw away 50% brake pads since I also do not understand why the second 50% would accelerate wear of the discs.
Does the compound change such much over pad thickness which leads to this?

BTW, I guess weighting will be more or less senseless since you cannot ensure that there is no "dirt" inside the disc which would lead to higher weight readings.

modernyankee

Understood. ;-D
Good point about the dirt. I hadn't thought of that. I suppose one could blow out the disks or do something else to clean them to the extent possible.

johnsopa

I took the rotors off myself (very carefully!) and took them (very carefully!) to my dealer and asked for them to be measured. They charged me about an hour total. IIRC correctly I got back three measurements per disc.

Did this two or three times, can't remember. I've since stopped measuring.

There's a good thread on this in the 991 GT3 forum, too. Swapping to irons is overrated. :-)

modernyankee

It would be super helpful if you could share your usage (how many road miles, how many track miles) and rotor measurements/readings with us if you have that info. Thanks.
BTW: I think I'm also part of that 911 thread, too. Good tip.

johnsopa

Check earlier in the thread, I posted two sets of measurements.

modernyankee

Sorry, John. I forgot you're the person who got me started on all this :-D (LOL) ...and I'm glad you did. There was a serious lack of good hard info about PCCB wear with track use. I'm sure you've see my data posts...and I'll post again this winter w/ the latest measurements (late Feb or early Mar probably). Last year I drove 13 track days and 1,372 miles. This year it was 23 days and 3,021 miles on track so I'm expecting my readings to have at least doubled and maybe tripled. And let's face it, we're only really talking about track-induced brake wear b/c (clearly) driving on public streets does nothing to cause wear on PCCB's (in one post, a fellow had 10 years and 90k miles on his PCCB's and was on the original brake pads!).

I get that the Carboteq measurements vary a bit...and I'm encouraged that your rotor wear seems to essentially match mine for the first year (but with you driving 50% more track days...so congratulations, you're using your brakes the way I'm attempting to train myself to use them...which is to say, less).
What I don't understand is: even with the inconsistencies inherent with measuring carbon content w/ the Carboteq tool, how do we rationalize effectively no change in your carbon content readings when you've nearly doubled your track days/miles/sessions? I'm going to be even more astounded if my Mar '23 readings show the same pattern. Naturally, I'll be puzzled...and also very pleased indeed! I'm also going to weigh the rotors this year. Stay tuned.

johnsopa

Be careful weighing them... There's lots of crud (rubber, etc.) trapped everywhere. I don't think you'll be able to get it all out.

modernyankee

Right...another poster mentioned the same thing. I'll do my best to look into and clean all the nooks and crannies.
BTW: I posted my brake wear info in the 991 GT3 Forum (b/c that's where I originally got hooked into the PCCB conversation). But just so this thread has a link to my post w/ all the PCCB measurements, here's the link.
https://rennlist.com/forums/991-gt3-...l#post18446576