Hi guys,
I replied to a post regarding the management of street and race friction on another forum earlier in the week, and thought my response could benefit some of the trackhounds on this board. This message is geared towards those who own a dual-use, daily driver / weekend warrior. Enjoy!
Typically a day or two before I go to the track, I put my race pads in. (I'm going this weekend, and I actually swapped mine in last night). If you did a proper bed-in cycle on your street pads, you should have a transfer layer of street pad material on your rotors:
http://www.stoptech.com/tech_info/wp...contents.shtml
Race pads are extremely abrasive when cold. Many are not designed to bite at low temperatures like street pads (although some
will bite more than certain street compounds). Therefore, they will grind away on your rotors when driven cold. So, when you drive them around on the street before the event, they'll scrape all of the street pad material off of the rotors. You're then starting with a clean slate when you get to the track. This is important, because certain street and race compounds don't play very nice when they're together on the rotor face. They may stack, and cause minor thickness variations which you will realize as a judder or vibration. Also, if you leave a lot of street pad material on the rotor face when you heat them up to 1000+ deg. F on the track, the material will "glob up" when heated, and again potentially cause vibrations.
So, a night or two before the event, insert your race pads in the comfort of your own home. Drive your car as normal, but allow more stopping distance, particularly in the morning when they're cold. The pedal will feel hard, but the pads won't have much bite, and you're going to have to push a bit harder to get results. Just leave some room when coming to a stop.
If you do have a good street pad layer on your rotors, they probably won't make too much noise when you first put them in. They'll be riding on the street pad transfer layer that's on the rotors. By the time you get where you're going however, there's a good chance you'll hear a nice screeching noise from your brakes. That will happen when you wear through that pad layer, and get back to the bare rotor iron. Race pads typically have a high metallic content, so the metal in the pad and the iron of the rotor make some nice music together. Visually, it will also be obvious when you've 'cleaned' the rotors. Again, if you bed your street pads in properly, your rotors should have an even blue-gray tint to them on the swept area (which is the pad material transfer layer). After you've driven around on the race pads cold, the rotors will revert back close to their original silver color because they will no longer be covered in pad material.
Okay, so your race pads are in, you've gotten your rotors cleaned up, and you're ready for the track, right? No! When you get to the track, you need to bed-in your race pads properly per the instructions in my link above. You can do it during your first session at the track, or if you can legally and safely do it on a road near the track, that will also work. To get the pads heated up, you'll need to hit significantly higher speeds then you do with street pads, so 60-5mph won't really work. You're looking at a 100mph starting point. With the race pads hot, they'll go into their adherent mode, and transfer on to the rotor face when they're hot enough. Get a good bed-in cycle done on the pads, and then you're ready to go full blast on the track. Drive your event and have fun.
After the event is over, the car has cooled down, and your gear is all packed up, drive the car home on the race pads. The goal is the same as it was before the event, clean your rotors. Since the race pads will be cold again, they'll be back into their abrasive mode. They will scrape off the race pad material that you transferred onto the rotors. Many times, the rotors will be pretty clean by the time you get home...stop-and-go LA freeway traffic takes care of that for me. You can also do some light dragging of the pedal on the highway on the way home from the event to scrape them a bit...but you don't want to get them hot enough to leave their abrasive mode. If the rotors aren't clean when you get home, you can drive them around town a bit to clean them up.
Now the final phase to get your brakes peforming their best on the street again...swap your street pads back in. Do a bed-in cycle on the street pads to lay down some street pad material on the rotors. That's it!
Each pad compound is going to react differently. Some race compounds cold are insanely abrasive. Hawk Blue comes to mind. They will eat your rotors at an unprecedented rate. So, you may only want to run them on the drive to the track, not around town for days in advance. A Pagid RS14 Black however, will not be nearly as agressive. Also, each pad will have a certain temp at which they'll become adherent. You won't need to reach the same speeds to get them up to temp so they'll 'stick' to the rotor face. You'll just need to do some experimentation with the different compounds to see what you like, and the best way to manage them with your rotors.
Pad and rotor management is extremely important to get the most out of your brakes. I used the methods above on my last car with our BBK, and I did over a dozen events on one set of rotors without a single vibration. In summary, clean your rotors, bed-in, clean, bed-in, clean, etc. You should do a bed-in every time you change your pads, and the rotors should be free of the prior pad compound when you do so. If you do it right, you'll only ever have one pad compound on your rotor face at any given time. You will get some additional wear on the rotors when running the race pads cold, but it's worth the tradeoff. If you don't clean them up and bed-in properly, you run the risk of uneven pad depositions, judders, and sub-par performance (something you really don't want to be distracted by on the track). Also, if the pad deposits are too severe, they sometimes necessitate replacement of the rotor...which gets expensive in a hurry. Finally, most people that run our rotors on the track on a regular basis will crack them past the point of no return long before they will wear them thin. So, it's not worth worrying about the rotor thickness wear.
I think that's about it. Let me know if anyone has any questions. Be safe, leave extra stopping distance with cold race pads, do your bed-in's on safe stretches of tarmac, and have fun.
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