ryoung

Last month I cracked one of the Alcons at Mid-Ohio. Saturday afternoon on the track, it sometimes felt like a rotor had warped, and this was particularly noticeable during the last session of the day. Later that evening at the hotel, I was looking at the rotors pretty closely and found two cracks that extended all the way out to the outer edge of the left front rotor.

The Good News: Since the rotors had seen probably 22k miles and 12 track days, they were getting rather worn, and I had already bought spares! Good planning, huh?

The Bad News: The new rotors were sitting at home, about 3 1/2 hours away. Maybe not such good planning after all :-(

So ... my brother Don (he was driving my S8 in the instructor group) and I get in his truck, drive back to Pittsburgh, pick up the rotors, and get back to the hotel at 3:00am. At 7:00am we're at the track swapping rotors. No surprise -- we were both a bit tired Sunday, especially on our drives home. Don had a 6 hr drive back to Chicago.

The 1st pic was taken after I got back from Mid-Ohio last year. At that point, the rotors had seen about 6 track days. The surface cracks probably look worse than they are, and this isn't really that unusual for a rotor that's seen a lot of heat. Heh, our cars are heavy.

The 2nd pic is the rotor as it came off the car last month. Both rotors had extensive surface cracks, but only the left front had two deep cracks that extended to the outside edge. I really do need to get some cooling air to these rotors.

<img src="http://pictureposter.audiworld.com/17157/rotorcracks.jpg">

<img src="http://pictureposter.audiworld.com/17157/alcon_cracked.jpg">

April

Sounds like any 'ol track day to me :-) That's one heck of a crack !

skiwi

what pads are you running?

ryoung

the rotors have seen six different pad compounds (See <A HREF="https://forums.audiworld.com/a8/msgs/29824.phtml">Dusty Brake Pads</a>.) The first picture with the surface cracks was taken after using the Pagid RS 4-4 Orange.

Of the track pads, the Ferodo DS3000 is my favorite by far. I experience zero fade, and because of the very high 0.6 coefficient of friction, it's very grippy and inspires much confidence. Since the rotors had seen 400+ track miles in the 22k total miles, I really have no complaints.

skiracer

is by cleaning (scotch brite works well) the edge of the rotor where the crack is and seeing if there is any depth to it? My guess is that the crack is superficial, and these rotors still have some life left in them (so long as they aren't warped!) You (and Don) really are hard on the brakes! Looks like FUN!!

ryoung

that one long vertical crack goes all the way across and thru to the vented center. Another crack about 90 deg around on this rotor does the same thing, but your're right, all the others are only surface cracks.

The other front rotor looks very similar, except surface cracks only. I think you've convinced me to hang on to this one and keep it as an emergency spare.

barryl

Hello Randy,

Those cracks are typical for rotors that have been
subject to track (ab)use. That is just the cost
of playing the game.

Getting more cooling will help a little, but if you
plan on running on the track, plan on replacing
rotors on a regular basis. On my track car, I change
the front rotors every other year, which is about
20-30 track days, MAYBE 2000 miles.

Your only mistake was on starting an event with
severly worn rotors. If you are going to drive on
the track, you need to take a real hard long look
at all your equipment. If something is suspect,
change it BEFORE you get on the track. That rotor
is close to coming apart. And when they do, the
results are always ugly. The typical result is that
the rotor separates and jams in the caliper.
That locks the wheel and sends you off the track.
Not fun.

Take care,
Barry

ryoung

Before Mid-Ohio, the rotor looked prety much like the 1st pic; and even now, that rotor is only down to a 31 mm width from 32. I had originally planned to replace these rotors after the event, even though wear is only half of the Audi spec limit of 2 mm of total wear.

I quess what I'm saying is that the sudden increase in "surface" cracks caught me by surprise. I was only lucky enough to catch this because I felt awarped rotor type of vibration and was examining the brakes closely.

BTW: I may have found a simple and inexpensive way to get cooling air to the rotors. I'll keep you posted.