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This is fantastic. I had no idea. Now I'm going to have to go around checking everyone's rotors. Of course, with manhole covers like I have, there's no way to know with the wheels on...
I bought two pimpin' GTS rotors a few years back, then had them plated to make them even more pimpin'. After installing them, I discovered I had two left feet up front....
As long as we're at it, what exactly are the holes for? Cooling, or giving water or steam a place to escape?
That's the theory. In practice the holes allow cracks to propagate faster and cut the life of the rotor.
Originally Posted by Rob Edwards
After installing them, I discovered I had two left feet up front....
You want to know what's really stupid? The Audi TTRS comes with directional front rotors. But, Audi was too cheap to have two SKUs. So, they've all got two left feet. Giant-a$$ed !@#$ing rotors that need at least a 19" wheel with Brembo calipers that make Big Reds look like go-kart brakes. But, the right side doesn't pump heat out of the rotor.
Just checked mine. Drilled Zimmerman's up front. Put on backwards by the PO or the shop he had do it. Car isn't driven hard so not a big deal I hope. I do have a new set of solid rotors wrapped in original boxes.
Just checked mine. Drilled Zimmerman's up front. Put on backwards by the PO or the shop he had do it. Car isn't driven hard so not a big deal I hope. I do have a new set of solid rotors wrapped in original boxes.
Well the good news is if they're Zimmerman's they probably aren't really "drilled", the holes are cast into the rotors. The ones you need to watch out for really were put on a machine and literally drilled.
Inspect them regularly for any signs of cracking and replace them. When they fail they fail catastrophically. I personally wouldn't take the chance, a pair of slotted Zimmerman's might run a couple hundred bucks and a rotor than comes apart on you at speed can ruin your whole day.
Last edited by Otto Mechanic; 03-31-2015 at 12:11 PM.
BTW, if you're using pads that don't off gas lots of folks argue you're better off with a plain old blank rotor. The only rationale I've heard (and believed enough to experiment with) for slotting is to keep a boundary layer of gas from forming between the pad and the rotors. I had such horrible brake fade when I started down this path I was ready to do just about anything I could to fix it, including ruby slippers if someone told me they'd work.
Some people maintain slots also help in wet conditions, I'm not sure I buy that one though since the rotors are hot enough to flash off water pretty darned fast, not sure how much vapor could form under the pads?
I've been happy with mine and my fade problem went away completely but I changed lines, pads and rotors all at once so I can't really say which change was most important.
After closer inspection...they are correctly installed
Well I got a big surprise when I pulled the front wheels to adjust the ride height. Based on the diagram near the top of this thread I just assumed mine were on backwards based on the hole pattern. The positions of some of the holes seemed like they might be part of the casting. Anyway, they are actually installed correctly, based on how the air should be drawn out. This photo is of the right front.
I bought new drilled Zimmerman rotors when I "upgraded" the rears to S4 calipers and noticed that both rotors were the same. When I contacted the seller I was told that's the way they are and it wouldn't make a difference. I'm not sure if the left rear rotor being on the right rear makes a difference or not but when the brakes get hot that one rotor does squeal like a pig. To this day it still pisses me off. Don't be so quick to blame the PO.
Just thinking about brakes, one would think it would be an ever-present tendency for rotors to warp, as thermal expansion wants to increase the circumference of the heated part while the inner cold part refuses to go along. The hot part is weak at high temperature, and might be inclined to do the wave thing. We all have cheap frying pans with warped bottoms - a similar effect.
An internally cooled rotor offers not just additional surface area on the inside of the heated rotor "skin", but has cold internal ribs that remain strong, more resistant to warping. (This effect is used to great advantage in air-cooled turbine blades, even though the cooling air is nearly 1400F - compressor outlet temperature.) The design not only allows for more extraction of heat, but also higher brake surface temperature through greater resistance to warping.
Maybe. I don't know much about brakes. I like to ponder design decisions, which can involve interesting interactions.
I bought new drilled Zimmerman rotors when I "upgraded" the rears to S4 calipers and noticed that both rotors were the same. When I contacted the seller I was told that's the way they are and it wouldn't make a difference. I'm not sure if the left rear rotor being on the right rear makes a difference or not but when the brakes get hot that one rotor does squeal like a pig. To this day it still pisses me off. Don't be so quick to blame the PO.
Hmmmm, interesting. You have one rotor on incorrect, and yet I'm not supposed to blame the PO? Further, this is not an aftermarket rotor, this is a bone stock Porsche part, it looks fairly new as well. Finally, although I consider the PO responsible for everything, I did mention my trillion dollar bet that it was a small shop that did the deed. So, I think if you can get pissed about it, I should be able to harbor some frustration as well. Notwithstanding I bought the car without an independent PPI(thx Bilal).
I can understand brake wear on the track because that's the name of the game, but in normal street driving brakes should last a l o n g time. -but then I'm one of those guys who lets off the throttle at least a mile before the stop. -then I oooze away from the light. My cars last a long time. Why do I own a 928? It's pretty.
I bought new drilled Zimmerman rotors when I "upgraded" the rears to S4 calipers and noticed that both rotors were the same. When I contacted the seller I was told that's the way they are and it wouldn't make a difference. I'm not sure if the left rear rotor being on the right rear makes a difference or not but when the brakes get hot that one rotor does squeal like a pig. To this day it still pisses me off. Don't be so quick to blame the PO.
Zimmerman rotors used to be much cheaper than OEM rotors- suggest you take a look at the rotor to see if the vanes are impeller like [spiral] or whether they run straight radially. If they are straight [a poorer/cheaper design] then they would be the same both sides. Just took a look at my rear rotors and they appear to be radial slots but then they could also be Zimmerman given I had some on my late S4 and not sure whether I retained the GTS rears or fitted the rotors that came off the S4 when we put my current 928 together. Appreciate if someone can confirm the configuration of the stock rear rotors.
Not sure squeal is the symptom I would be looking for- that is usually a sign of brakes "doing their work". I run with Hawk Street Plus or whatever they are called and they squeal something awful under light braking [not under heavy braking].
Regards
Fred
Last edited by FredR; 03-29-2015 at 11:40 AM.
Reason: checked my rear rotors
03-28-2015, 06:02 PM
