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Old 10-29-2012, 10:08 AM   #1 (permalink)
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how do you tell when rotors are done?

I got some CL RC6 racing pads coming for my next track adventure. last time my "performance streets" got a little scary by the end of the day.

anyway, i hear these pads are aggressive and wear the rotors pretty quick. plus I been reading the threads where everyone else talks about how fast they go through track pads and rotors.

that said, if the rotors arent warped or cracked, is there a quick visual inspection to tell what you got left? how can you tell when they are about done? or do you just run them until they crack or warp? dont really want to do that without a spare set at the track.
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Old 10-29-2012, 01:51 PM   #2 (permalink)
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Re: how do you tell when rotors are done?

I run them until the cracks are big enough to catch the edge of a fingernail. A billion surface cracks are perfectly normal. You don't want them to open up.

I've never got a front set close to minimum thickness before cracking them badly, but half the time the rears last until they reach minimum thickness. Be sure think about anticipated rotor wear for the next event when computing your minimum.

I always take an extra set of rotors. I'd hate to miss an event for a common wear item. The rears will fit inside the box with the fronts, so they don't take much space.
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Old 10-29-2012, 02:59 PM   #3 (permalink)
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Re: how do you tell when rotors are done?

good to know the gaging method and good idea on the spares. Thanks
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Old 10-29-2012, 05:37 PM   #4 (permalink)
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Re: how do you tell when rotors are done?

I measured my pads when they were new so I could determine when they were 50% worn (very easy with a measuring caliper - I'm referring to the tool - not the brake caliper).

For the rotors - a visual inspection after each track day, and after each session as they really start to wear. I had a set of DBA 5000 on the front that lasted the season (approx 26 track days including 8 days at "big/fast" tracks). When they started to crack we watched wear closely. A couple weeks ago we noticed a crack on the inside heading toward the hat, that stretched across half the face of the rotor. By the end of the track day the crack migrated through the hat to the very edge. That was when we said "DONE".

It's in storage till next year. I didn't want to rush to replace rotors for a couple more track days. I'd rather take my time since I"m considering changing rotors next year and not sure what I'll choose. The rear (DBA4000) are fine, and I happen to have an extra set - but won't change them until needed.
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Old 10-30-2012, 06:14 PM   #5 (permalink)
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Re: how do you tell when rotors are done?

Anyone know what the thickness of DBA 4000's are when new? Thanks, John
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Old 11-19-2012, 11:25 AM   #6 (permalink)
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Re: how do you tell when rotors are done?

Wow, a crack thru the entire depth of the face is bad enough. When it gets into the hat? That's dangerous catastrophic failure territory.

Lots of cracks in the rotor surface is indeed common but shouldn't be considered acceptable. Sounds like some cooling is in order. Installing cooling is a PITA but it pays dividends in making your stuff last longer. Sure brakes are a wear/replacement item. But why not make them last longer and reduce consumable costs?
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Old 11-20-2012, 04:03 PM   #7 (permalink)
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Re: how do you tell when rotors are done?

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Originally Posted by ktlspider View Post
Lots of cracks in the rotor surface is indeed common but shouldn't be considered acceptable. Sounds like some cooling is in order. Installing cooling is a PITA but it pays dividends in making your stuff last longer. Sure brakes are a wear/replacement item. But why not make them last longer and reduce consumable costs?
If you have a cooling solution for eliminating minor surface cracks in rotors used with race pads in HPDE conditions, you should certainly share it.
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Old 11-21-2012, 08:09 AM   #8 (permalink)
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Re: how do you tell when rotors are done?

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If you have a cooling solution for eliminating minor surface cracks in rotors used with race pads in HPDE conditions, you should certainly share it.
Well I can certainly do that. But let me say that I never said my solutions are going to completelyeliminate the cracking. Some of that cracking is attributed to cheap rotors. My point was to say that cracking should not be something that is considered minor/normal and that some time spent figuring out how to get the brakes cooler is time & money well spent because it only serves to save you money in the long run.

There are plenty of cooling solutions out there for people to look for. It doesn't have to be a retail purchase. Even something as basic as a length of hose pointed at the caliper can be beneficial. One of the first things people should do is remove the splash shields. These shields block a lot of the air that goes under the car from getting to the brakes.

A good example of what brake cooling can do is a "test" that occurred on a friend's car. Car is an old Porsche that the guy drives the heck out of. One of those guys that has great reflexes and car control skills (cornering AND braking), and if he'd clean up his lines/technique he'd be silly fast instead of stupid fast.

He was content with the stock brakes & race pads because a) he's on a tight budget, b) he's cheap, c) if it ain't broke, don't fix it (he is a Jeep technician in the day job, doesn't care to work on cars any more than he has to), d) hey K-man, don't try to out-engineer the Germans (he's German himself)

Well, that being said, the stock brakes are good but certainly can be improved upon. We did some tweaks to the brakes that involved installing a slightly larger front rotor and a different stock caliper from a later model car. The rotor increased in diameter by 20mm -less than an inch- and got slightly wider (+4mm), which adds some heat capacity. The front ducts in his racy fiberglass nose were put to use with the setup in the attached pictures- basically hoses run from the front bumper into the rotor.

The result is instantly apparent. The brake adjustment tweaked the front/rear bias a bit but it also added MUCH needed cooling up front. His braking is more consistent, pads last MUCH longer (at least twice as long- on BOTH ends of the car) no more bleeding brakes before each event. Sure it cost some money but there's "no free lunch" in life.

Attached are some examples of what i'm talking about

One is a scoop from a late 90's Porsche on a mid 80's Porsche. It works surprisingly well. These scoops have been standard on most Porsches since the early 90s. I needed nothing more than a drill and some zip ties to firmly attach it to the A-arm.

The other pictures of the red car show the ducting from the front bumper to the back/eye of the rotor. Forgive the use of silver duct tape. I had to use it to protect the silicone hose from abrasion on the body The only retail purchase was some aluminum backing plates with the hose "nozzle". These plates are VERY handy to get the cooling air right where you want it- into the eye of the rotor so the rotor is cooled thru the vanes/vents in the rotor.

Another key to making your cooling effective is avoiding sharp bends in the hoses and sealing up the ducting going to the rotor. Since the air coming into the duct is very low pressure, any bends or leaks in the system drastically diminish the efficiency of the air flow. So you want the biggest hose you can get in there and no obstructions.

Sorry for the non-Vette pictures. I've done most all my work thus far on BMWs and Porsches. But the cooling stuff is somewhat universal in that you use whatever you can find to get air to the rotors, regardless of what kind of car we're talking about. I've seen people come up with all kinds of ingenious uses of everyday parts. One guy made his rotor backing plates out of the sheetmetal surrounds from his benchtop grinder! Other people have used Shop Vac hose attachments to scoop air from under the A-arm to the hose. All you gotta do is come up with a solution that is somewhat durable so it can handle the occasional off-track farming adventure and withstand the speed you'll be going. Some Vettes are really hauling arse at 150mph+ at the loooooong tracks!

Honestly a big downside to the brakes are the dreaded sliding calipers. Those things are junk. Fixed calipers are not cheap but they do a MUCH better job of dealing with pad taper and poor pad balance (inboard pad wears more than outboard).

Good luck and keep the shiny side of the car up!
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how do you tell when rotors are done?-p62106721115757115.jpg   how do you tell when rotors are done?-cimg67961256589089.jpg   how do you tell when rotors are done?-cimg67981256589193.jpg   how do you tell when rotors are done?-cimg67991256589284.jpg   how do you tell when rotors are done?-cimg67971256589147.jpg  

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Last edited by ktlspider; 11-21-2012 at 08:12 AM. Reason: forgot to compete a sentence
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Old 12-07-2012, 08:53 AM   #9 (permalink)
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Re: how do you tell when rotors are done?

I just wanted to report back on those CL RC6 pads. my comments are HOLY CRAP THIS THING STOPS! I dont have an extensive experience with race pdas, so I can't compare. previous car was a miata, way less power and weight, so performance street pads were adequate. but I found performance stret pads were not on the Z06. amazing difference. where I was hitting 135 before, I was doing 142 at the end of the strights, mainly becuase I could stay in it longer and dive bomb the brakes and they would take it all day. I won TTA and set the class track record, and won some hoosiers. so i am happy.
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Old 12-07-2012, 04:43 PM   #10 (permalink)
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Re: how do you tell when rotors are done?

Quote:
Originally Posted by trigger View Post
I just wanted to report back on those CL RC6 pads. my comments are HOLY CRAP THIS THING STOPS! I dont have an extensive experience with race pdas, so I can't compare. previous car was a miata, way less power and weight, so performance street pads were adequate. but I found performance stret pads were not on the Z06. amazing difference. where I was hitting 135 before, I was doing 142 at the end of the strights, mainly becuase I could stay in it longer and dive bomb the brakes and they would take it all day. I won TTA and set the class track record, and won some hoosiers. so i am happy.
I once had a passenger tell me he felt like a piece of cheese being pushed through a grater in the braking zones.
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