Planet 9

astoddard · #1 03-13-2009, 09:51 AM

The last time I was at the dealer they recommended replacement b/c the cracking. Are they right, taking track use into consideration?

mdavis · #2 03-13-2009, 09:55 AM

I had to replace my front rotors after 8 track days and approximately 40K miles. They had no cracks.

beez · #3 03-13-2009, 09:56 AM

I'd say you're getting very close. Some cracking around the holes is to be expected, but keep an eye out for cracks that connect two or more holes... as soon as you see one of those, it's time to get new rotors... Will these take another track day? Maybe, but if you use them for another track day, I'd monitor them very closely.

brad

astoddard · #4 03-13-2009, 10:13 AM

These have ~25 track days on them and 18000 total vehicle miles (these are the stock rotors). I noticed that the rotors were taking more of a beating when I started using Pagid orange pads last year. I am more inclined to be cautious and replace now, esp w/ brakes, rather than having my track weekend ended early.

The next decision is whether to go with the stock rotors again or something like the Girodisc w/ seperate hat floating rotor design.

**KS-CS** · #5 03-13-2009, 10:13 AM

It looks like you have at least a 1 mm lip around the edge of the rotor, in which case it would be time to replace them anyway, irregardless of the cracks. Porsche recommends replacing the rotors when they lose 2 mm thickness (total thickness).

***bh2106*** · #6 03-13-2009, 11:03 AM

I've seen a rotor shatter on a race car. Not only did the day end early, it ended quite badly, with a very twisted car.

I'd buy some non-drilled rotors for track use.

mdavis · #7 03-13-2009, 11:30 AM

Originally Posted by astoddard

These have ~25 track days on them and 18000 total vehicle miles (these are the stock rotors). I noticed that the rotors were taking more of a beating when I started using Pagid orange pads last year. I am more inclined to be cautious and replace now, esp w/ brakes, rather than having my track weekend ended early.

The next decision is whether to go with the stock rotors again or something like the Girodisc w/ seperate hat floating rotor design.

I agree - - don't take chances with brakes and tires as a general rule and especially on the track. Doing so can lead to bad things!

**blueone** · #8 03-13-2009, 12:04 PM

Originally Posted by astoddard

These have ~25 track days on them and 18000 total vehicle miles (these are the stock rotors). I noticed that the rotors were taking more of a beating when I started using Pagid orange pads last year. I am more inclined to be cautious and replace now, esp w/ brakes, rather than having my track weekend ended early.

The next decision is whether to go with the stock rotors again or something like the Girodisc w/ seperate hat floating rotor design.

I agree with replacing the rotors now. That's just a risk not worth taking.

I was never very happy with two-piece rotors on the track. The discs are usually expensive (because they are low-volume, precision-machined things) and the swap takes a lot longer than with single-piece rotors. I liked cryo-treated single-piece grooved rotors, and I saved the two-piece numbers (I used AP brakes at that time) for the street, after the first set of discs wore out.

**STLPCA** · #9 03-13-2009, 01:18 PM

Replace rotors at the first to occur of:

1. wear close to approaching the minimum thickness, or
2. cracks close to joining 2 holes or running to the rotor's edge.

For track I'm more conservative and don't start a DE event if I'm not confident my rotors (& pads) will easily make it through to the end. Were it me, I'd replace your rotors rather than sweat it out. Apart from a catastrophic event which generally follows an exploding rotor, as I'm sure you know, worn rotors and/or pads are more prone to fade.

BillL223 · #10 03-13-2009, 06:19 PM

The rotors look about like mine. However, I miked mine and only .016" wear in the front and .008" wear in the rear. No cracks connecting. Use a washer on each side under of your micrometer or caliper to get a good measurement then subtract the washer thickness to get rotor thickness. If thickness is O.K., I would run them.

**blueone** · #11 03-13-2009, 07:17 PM

Originally Posted by BillL223

The rotors look about like mine. However, I miked mine and only .016" wear in the front and .008" wear in the rear. No cracks connecting. Use a washer on each side under of your micrometer or caliper to get a good measurement then subtract the washer thickness to get rotor thickness. If thickness is O.K., I would run them.

Why use washers? Is that for the case where you use a conventional micrometer rather than a disc brake micrometer?

**facelvega** · #12 03-13-2009, 10:39 PM

From a current discussion on rennlist: Result of rotor failure.

The reason to err on the side of caution: rotor failure will happen when you are braking very, very hard - and the results will be very, very bad...

**jurnes** · #13 03-13-2009, 11:53 PM

Porsche rotors have the minimum allowable thickness stamped on the hat area of the rotor.

I had my OEM rotors turned after 4000 miles on the car and 8 DE days (Thunderhill and Laguna Seca). I still have 1 mm to play with.

You can use a micrometer to check the thickness of the rotors in question. The cracking issue is a visual, and as others have stated.

**Craig@Rennstore.com** · #14 03-15-2009, 10:54 PM

Consider the Girodisc fronts - considering they last longer than OEM, the additional cost is not 'that much' -