Did DSC warp my rotors at the track?

[RussRamz]

To clean up your discs, use this:

http://multimedia.3m.com/mws/mediawe...SevTSeSSSSSS--

re-bed your brakes (properly) and you'll be in fine shape. I've used the above method and it revives the hot brake shimmy very nicely.

[mhrir]

Originally Posted by RussRamz

re-bed your brakes (properly) and you'll be in fine shape. I've used the above method and it revives the hot brake shimmy very nicely.

Seems straight forward. I will give it a go.

I am trying to recall what pad deposit means... Do I need to switch to a harder or softer compound for the rear pads?

[RussRamz]

Originally Posted by mhrir

Seems straight forward. I will give it a go.

I am trying to recall what pad deposit means... Do I need to switch to a harder or softer compound for the rear pads?

Your brake pads will always build-up on your discs--eventually. The trick is to apply those deposits uniformly. Here is a good set of instructions on how to properly bed-in a set of brake pads on a new disc. If you strip the disc of the brake pad material using a paint stripper, you will need to re-bed the pads. This is for Stoptech brakes, but the same method applies to any set of brakes and pads. The key is to differentiate between the pads and the method to use. You will want to make sure you have a safe place to do this. I do not recommend doing this on a road for two reasons: you will unlikely keep the temperatures up long enough to conduct the repeated braking and the other reason is other traffic.

http://www.stoptech.com/tech_info/wp_bedinstock.shtml

[lucid]

Originally Posted by The HACK

Cracks on tracked rotors is a sign of life. Unless the cracks run all the way from the edge of the rotor I wouldn't worry about it.

+1

Originally Posted by The HACK

Before anyone says "well you don't brake hard," well, I don't. The less you have to brake the faster you will go.

I will say this. The two "home tracks" for me, California Speedway in Fontana and Buttonwillow Raceway in Buttonwillow are two very brake intensive tracks. Cal Speedway has a 120mph -> 40mph HEAVY braking zone, a 90mph -> 30mph HEAVY braking zone followed by a 180 degrees decreasing radius hairpin, and a 115mph -> 35mph HEAVY braking zone followed by a combination of fairly slow turns. Buttonwillow has 3 back to back to back 100+mph braking zones. These brakes gets put through the torture chamber at least once every other month throughout the year.

Not really. If we assume that everyone is capable of flooring the throttle on a straight, going faster boils down to cornering faster, which means corner entry and exit speeds are higher. Higher entry speeds do not simply mean you are braking less. Since the exit speeds will also be higher, the peak speed prior to getting on the brakes will also be higher (some other corner you are now taking faster is leading to that straight). And, relatively speaking, you convert more energy to heat when you brake from higher speeds (kinetic energy = .5 * mass * velocity^2, so the equation is more sensitive to top speeds).

In other words, if you were to go faster and take that same 40mph corner at 50 mph, you wouldn't be necessarilly braking less because since you are faster you must now be approaching that corner at a higher straighaway speed, say 125mph ( a guess). If you do the math on kinetic energy change for those 2 scenarios, you'll see that the faster scenario will result in more kinetic energy loss (as heat).

And, I am not sure but what you mean by "heavy" braking. Who would want to decelerate from 120-40 "lightly" on a track? I don't know west coast tracks, but what you describe above does not sound particularly demanding on the brakes. Try Watkins Glen.

I suspect the long service life of your rotors has a lot to do with their superior cooling vane geometry (compared to stock), and the resulting increase in the heat transfer coefficient.

[The HACK]

Originally Posted by lucid

I suspect the long service life of your rotors has a lot to do with their superior cooling vane geometry (compared to stock), and the resulting increase in the heat transfer coefficient.

I suspect so too. The amount of wear is certainly far less than what I'm used to with OEM rotors on other cars. In fact the rate of wear is more indicative of cars with big brake kits and multipiston calipers.

Most of what you wrote wrt braking, is correct. I over-simplified the concept of "braking" in relation to speed on the learning curve. The physical aspect of going fast is correct, you will have to dissipate X amount of energy for each turn in order to go through it at Y speed.

The part about "braking less" makes you go faster, is in relation to the learning curve. I found that, as a driver, most of us tend to brake too much. As we progress, some of us eventually shed that habit and find the optimum amount of braking to use, which is as little as needed for as little time as possible to get to your optimum turn-in speed.

Actually, one "sage" once told me, that brakes are actually just another tool to manage weight transfer, once you learn how to use the brakes strictly as a tool to manage weight transfer, you will have found the least amount of braking you need for each turn, and therefore the maximum entry speed that will allow you to carry the highest speed through the turn and therefore maximum entry speed...Which is the secret to go fast.

Since on most weekends I'll go through the progression from working with beginners to intermediates to advanced students, this is what I typically see. Car control students who's never activated ABS their entire life, don't brake nearly enough. Then you get beginner track students...They brake either way too much or way too little. Intermediate guys who's learned to control their braking a little more, consistently brake too much. The advance guys brake only as much as they need.

As for the "heavy" braking comment, the entry from the banking to the infield is a short little straight where you don't have the luxury to extend your braking zone too far to save your brakes. You're right, nobody brakes "light" for these situations, I meant "heavy" as in all your braking needs to be done in a short compact space and time and there's little room for error and you can't really extend your braking zone much since it's coming off of a long sweeping turn at high speed. Maybe "difficult" would be a better word for "heavy" in reference to braking in this context, in that it's followed by two very tight turns at low speed and therefore you don't get much of an opportunity to let the brakes cool-down before you have to brake for another hairpin.

[blender]

Since your post asked about DSC - how long/how often is your DSC light on? I see mine about five to eight times a day on a 'spirited' weekend drive, but rarely for more than a second or three each time. If your car is similar I doubt that DSC-initiated braking is the primary cause of your warped rotors - probably just normal [intense] braking as indicated in this thread.

[lucid]

Originally Posted by The HACK

I suspect so too. The amount of wear is certainly far less than what I'm used to with OEM rotors on other cars. In fact the rate of wear is more indicative of cars with big brake kits and multipiston calipers.

I have about 30 days on the OEM EVO rotors on my E30 M3, and they still look good and have thickness to spare. They are being properly cooled, and I suspect that is the main reason there as well.

I was using cobalt pads on other cars, switched to carbotech, and I am thinking about going back if I track the Z4M again. They are pretty solid and last longer I think. But I am just sick of paying $400 a set for OEM pad shapes. I'm going to wilwood calipers on the E30 just to cut back on pad expenses (they are more like $150 a set).

The other thing about braking less is learning to use the tires to scrub some speed at entry. I improved my lap times significantly when I started doing that better. It helped to ride shot gun with one of the fastest racers in the area to see what was possible.

[BruceJ]

Originally Posted by mhrir

It is hard to get excited about a link to rotors that are backordered...

I have since switched back to the OEM pads. From cold there is a slight pulse in the pedal when stopping. As the brakes heat up that pulsing gets progressively stronger, although nothing like what I was experiencing at Road America. There are no detectable deposits on any of the rotors (unless it is invisible) so I don't think that is the issue. While changing the pads, I spun the rotors and could not detect any warp with my eyes for what that is worth.

The best my butt sensor can tell is either the left front or left rear rotor is the culprit. I've already purchased new OEM rotors for all four corners to have as spares, so I am going to replace one at a time until it goes away.

The only other clue that I did not mention was that the left rear caliper piston was pushed all the way in when changing to the street pads. When I was at the track I could hear a slight rattle coming from the left rear when driving slowly over bumps (which I did not relate to my warped rotor issue). I duplicated this rattle at home by jiggling the inboard pad since it had plenty of space between the rotor and piston. It did not rattle when braking. I pushed on the brake pedal and the piston came back out and stayed. This is what makes me think it is the left rear rotor that is warped. As it gets hot it warps more which in turn pushes the caliper piston in.

Or maybe I should have my junior detective badge revoked...

If your foot and your butt are telling you that your rotors are warped do the simple thing and get them checked for runout. Maybe some old mechs can tell with the naked eye but theres very little argument once you put the dial indicator on them. Beats flying off a curve at 120 plus.

[Shipkiller]

Originally Posted by BruceJ

If your foot and your butt are telling you that your rotors are warped do the simple thing and get them checked for runout. Maybe some old mechs can tell with the naked eye but theres very little argument once you put the dial indicator on them. Beats flying off a curve at 120 plus.

checking the rotors on the ///M for runout is a royal pain in the a**.

[BruceJ]

Originally Posted by Shipkiller

checking the rotors on the ///M for runout is a royal pain in the a**.

Presuming you have scrubbed and bedded previously with no satisfaction, what would you do short of just replacing until you fixed the problem?