Originally Posted by wonho
Hack, I find your dissertations very reasonable, enlightening, and even enjoyable to read. And this one has given me an emphasis on the importance of PROPER break-in. I didn't know the brakes were such delicate machines btw.. I do daily-drive these pads, so weird deposits are most likely inevitable. And this past time, I didn't break them in properly; I just used the first a few laps as warm up and break-in.
Again, thanks a lot for your time on this, and I will definitely try a few solid sessions of break-in prior to my next event, as well as exploiting some venting options, and report back with results!
They (bed-in) are only really necessary if you change pads between the street and the track. If you leave them on all the time, re-bedding them may not necessarily yield better results.
Although, on some of the more aggressive track pads, if you drive on them COLD, they'll scrape away the top layer of deposit and thus you'll have to bed them in again the first session. Typically, at the events I attend, I'm given a 15 minute orientation session in the morning before the track goes completely hot, and I use that opportunity to "bed-in" because I switch back and forth between my street compound and my track compound. If you're not afforded this luxury, and the pads are starting to get low (below 50%, that is), I would take it easy on the brakes for the first few laps, let it come up to temp more easily, and make sure your last lap on the track for the first session you do not use the brakes AT ALL. Then once you park it, the brake vibration and shudder you experienced should not come back in the next sessions no matter how hot and how hard you drive...Unless it's heat related problems.
It's that last lap without the brakes that will cool off the rotors effectively by providing adequate airflow to the system, IMO. Otherwise it's entirely possible to have the rotor hold temp until you're in the pits, and on the later model BMWs (2006 and later) the system is designed to hold slight pressure on the calipers to force the pads in contact with the rotor, especially if you park on an incline, resulting in additional transfer of pads (especially if the rotor is still HOT).