brake disc question

[speedman]

What are the best cross drilled brake rotors to buy

[Emission]

For looks? For track use? For the shortest stops?

[Bill Verburg]

Originally posted by speedman
What are the best cross drilled brake rotors to buy

Only buy factory

[speedman]

street use and why only buy factory

[Bill Verburg]

Originally posted by speedman
street use and why only buy factory

For street use it doesn't matter, but the factory ones are done correctly. The holes are cast in and then stress relieved. There is no aftermarket disk that is done this way, they all drill raw castings

[speedman]

will the drilled hole units crack under normal streetuse

[John Z. Goriup]

Yes, there is an aftermarket maker of high quality OEM equivalent rotors, which have the necessary cast-in holes in the correct locations plus the chamfering: Zimmerman...made in Germany. I have had very good luck with them, they last, and I've never had one crack.

[Zeke]

Originally posted by speedman
will the drilled hole units crack under normal streetuse

What is "normal" street use? Fairly hot brakes and you hit some water. Is that "normal"? Listen to Bill.

[speedman]

If zimmerman cast their holes like the OEM wouldn't they be as good. I thought that Porsche AG bought there rotors from zimmerman

[Bill Verburg]

Originally posted by John Z. Goriup
Yes, there is an aftermarket maker of high quality OEM equivalent rotors, which have the necessary cast-in holes in the correct locations plus the chamfering: Zimmerman...made in Germany. I have had very good luck with them, they last, and I've never had one crack.

Zimmerman has been an oem supplier for various models, they make fine rotors, just not quite as good as some other suppliers, I suspect that may be why Porsche moved on.

[Bill Verburg]

Again, for street use it doesn't matter at all

[randywebb]

THx - I didn't know P AG had shifted suppliers.

[Wil Ferch]

Although stated many times..and repeated often...are factory rotors indeed cast vs others drilled ???

See inconclusive posts here--->

Are rotor holes really cast or drilled?

- Wil

[Yellowbird RS]

love my Brembos!

[randywebb]

Originally posted by Wil Ferch
Although stated many times..and repeated often...are factory rotors indeed cast vs others drilled ???

See inconclusive posts here--->

Are rotor holes really cast or drilled?

- Wil

very true - but Bill's post above is very clear. so I assume he checked it out.

[Bill Verburg]

Will you can pick and choose threads that show what you wish to show all day.

930, 993, 996 holes are cast in I posted pictures of the molds, I have the patent document somewhere on my computer.

Here's half of one of the masters

[Grady Clay]

Bill,

So I can understand the process: This is half of the pattern to make the center piece of the mold. There are other patterns to make the two outer mold pieces. The outer pieces have the holes in them that align with the half-moon cut-outs in the supporting ribs (vanes) of the center piece. The final mold consists of the inner piece, two outer pieces and the outer mold housing. Once assembled the rotor is cast. In the machining process the holes are left as cast (just like the rest of the interior).

Great design. I particularly like the half-moon in the internal ribs. I think the turbulence there adds to the heat transfer. Having the perimeter of the holes supported by the rib reduces the stress at the hole, preventing cracks. I also like the extra little support rib.

I’m convinced. These will be my next set of rotors.

Best,
Grady

[Wil Ferch]

Bill:

I wasn't trying to be argumentative.....the referenced thread did not make it expressly clear ( at least not to me!) that a definite conclusion was reached......

Here's a thought...even for those rotors that are "post-mfr-drilled"...would a tedious individual polishing of the hole circumferential surface...be OK to avoid subsequent cracking by removing local stress-risers ???

In addition....I believe having a row of ( say) three holes (vs four holes...with the 4th one coming close to the disc diameter-edge)...might be better to avoid / delay cracking?? Meaning..the last hole is not as close the edge as before ??

- Wil

[Bill Verburg]

Originally posted by Wil Ferch
Bill:
Here's a thought...even for those rotors that are "post-mfr-drilled"...would a tedious individual polishing of the hole circumferential surface...be OK to avoid subsequent cracking by removing local stress-risers ???
- Wil

No, they are not designed for it, they aren't even needed as much w/ modern pads. Current thinking for 996/997 Cups and RS w/ steel rotors is slotted like this Brembo for GT3

Originally posted by Wil Ferch
Bill:
In addition....I believe having a row of ( say) three holes (vs four holes...with the 4th one coming close to the disc diameter-edge)...might be better to avoid / delay cracking?? Meaning..the last hole is not as close the edge as before ??

- Wil

I become increasingly uncomfortable as the hole approachs the edge, they were not designed like that. You will see it when a lage diameter rotor is machined down.

[Wil Ferch]

Machined slots...although statistically better at showing cracks...are not immune from this either. As you can see from the Brembo/GT3 pics...successful slots should be formed with gentle radius edges and bottoms to the cut....not a sharp "U" which would introduce a whole new set of stress risers.

- Wil