Cayenne brakes - more info on rotor selection, and compendium of my previous posts.
08-11-2007, 12:42 PM
#1
AudiWorld Super User
Thread Starter
Cayenne brakes - more info on rotor selection, and compendium of my previous posts.
Hey guys,
I have typed out alot of this info within specific correspondance, and I also wanted to put this down here to reduce the roughly 3 islands of information holding all this info on my side. It will also be of value of anyone looking to homebrew rotors, whether OEM or whatever. That said, this will read alot like Paul's letters to the Galalatians, but where Paul is a guy named Bob who slips easily between SI and Imperial measurements, and who has alot of stuff going at any given moment.
First off, I had a convo with a guy named Joe, wherein I detailed the exact measurements you'd want, based on measurements I took of the whole setup:
As a reminder, I used Mercedes Benz rotors, part number 203-421-09-12. These rotors are 1.190 (27mm) wide rotors at the braking ring, and when lying flat on a table, are 1.845" high, with a .230 thick flange, for an "underhat measurement" of 1.615". This concept of an "underhat" measurement is one you should become familiar with, as it best details where the rotor will ride on the vehicle, regardless of the thickness of the actual hat material.
My chosen rotors did need some modification: The centerbores did need to be opened up to mate with the 2.680" centering boss on the allroad hub, which also has a radiused edge on the inside (meaning a small amount of additional material must be removed on the rotor, even after opening it up to 2.68", to accomodate that radius). The lug holes also needed to be opened up from 12 to 14mm (I used a step bit).
That last, revelatory discussion with Joe:
"
... I measured the rotor, and in an
ideal world, its centerline would be offset .05"
more towards the inboard side... and this is from
an under-hat measure of 1.61"-ish, which I believe is
fairly precise. And, the rotor face is 27mm thick.
Pardon the mix of imperial and metric.
This boils down to an ideal underhat measurement
of 41mm for this rotor, which has a face of 27mm.
(1.61"+.05", in mm)
Therefore, the ideal measurement from underhat
surface (hub surface) to centerline of braking
width is 27.5mm, with optimum braking width
around 30mm.
That should be my best guide for choosing rotors.
"
So, the idea here, is that there isn't an ideal "underhat" measurement, since the width of the braking surface is also important. So, what is really important is the width between the underside of the hat flange (which abuts the hub), and and an imaginary centerline drawn through the middle of the braking ring.
Let's say that the ideal braking ring is 30mm wide. Here, with the rotor laying flat on a table, the centerline for that ring is 15mm high. Since you're looking for an ideal centerline-to-underhat measurement of 27.5mm, then you'd want an overall, underhat measurement of 42.5mm high (from the table to the underside of the hat).
Here's another email I traded today with a guy named Paul, who was looking at the 220-421-11-12 rotor:
"I have measured the "-11-12" rotor as well, and
it is not the offset you need.
The 09-12 rotor is the one you need. It measures
roughly 1.61" under the hat. The height to the
top of the hat is 1.845, and the flange is .230
thick. Braking ring is 1.190" thick.
220-421-11-12 measures almost double that, which
is 3.00 to the top of the hat, and a .243 thick
hat. The braking ring width is 1.262, or quick
mental math, around 30mm (1"=25.4mm).
The 09-12 rotor corresponds to 2002-2004 AMG C32,
and 05-06 C55 AMG.
I hope this helps,
Bob
"
Typing this out means I should finally list my findings of other, 345mm-diameter rotors that I found. I will list part numbers if I have them.
Measurement legend:
ML55 rotors, 2000-2003:
31mm thick braking surface
Overall height: 2.050
Flange thickness: .275
ML430 (I think this is the 2000-2005 stretch), 30mm thick braking surface:
Overall height: 2.060
Flange thickness: .275
Toureg, the 345-ishmm rotor version (there may be many braking versions on this vehicle, not sure):
350mm diameter, 34mm braking width (which may be too wide for the cayenne calipers!)
Overall height: 2.750
Flange thickness: .350
Now, remember, all of the above are 5 lugs, but are not 112.5 (or whatever the allroad dimension is). They are all larger, but that's ok - since they are 5 lug, they can either be redrilled just out of phase (virgin holes) or otherwise adapted. It's not a dealbreaker.
S8 rotor, 2001 (which I believe is around 31mm):
Overall height: 2.395
Flange thickness: .295
I believe this next set of measurements is from a B6S4. This is from a frantic scribble of notes I transcribed from my phone that I made last time I had it in for service. I honestly am not sure, but I believe it is the B6S4, since I recall that as being JUST too shallow of a rotor.
Overall height: 46mm
Flange thickness: 8mm
One rotor I never checked was the S500 Armored Body, 2004-2006, 30mm braking width. It's MB part number 220 421 19 12, and the rotors are US$900 or something each - needless to say, I did not order these "just to try them."
I think there are other rotors as well. I detailed the discovery process in another post, btw. I did not look at any 6 lug rotors, and I may have even limited my search to just a few marques.... I honestly don't recall all criteria of my search.
But, as a capstone to this bloviation, here are all of my links:
<a href="https://forums.audiworld.com/allroad/msgs/201746.phtml">Overall details and information on fasteners I chose</a>
<a href="https://forums.audiworld.com/allroad/msgs/201215.phtml">Initial impressions as a passenger and recollections on MB Part numbers</a>
<a href="https://forums.audiworld.com/allroad/msgs/200907.phtml">Initial impressions as a driver</a>
<a href="https://forums.audiworld.com/allroad/msgs/200159.phtml">Quick statement of part number and quick explanation of measurement used</a>
<a href="https://forums.audiworld.com/allroad/msgs/200011.phtml">Teaser pic, Quick explanation of machining required, Brakeline mention</a>
<a href="https://forums.audiworld.com/rockymtn/msgs/97900.phtml">How I found all of these candidates (methodology on discovery and first hand measurement)</a>
This is great - I can now throw away like 8 pieces of paper.
I have typed out alot of this info within specific correspondance, and I also wanted to put this down here to reduce the roughly 3 islands of information holding all this info on my side. It will also be of value of anyone looking to homebrew rotors, whether OEM or whatever. That said, this will read alot like Paul's letters to the Galalatians, but where Paul is a guy named Bob who slips easily between SI and Imperial measurements, and who has alot of stuff going at any given moment.
First off, I had a convo with a guy named Joe, wherein I detailed the exact measurements you'd want, based on measurements I took of the whole setup:
As a reminder, I used Mercedes Benz rotors, part number 203-421-09-12. These rotors are 1.190 (27mm) wide rotors at the braking ring, and when lying flat on a table, are 1.845" high, with a .230 thick flange, for an "underhat measurement" of 1.615". This concept of an "underhat" measurement is one you should become familiar with, as it best details where the rotor will ride on the vehicle, regardless of the thickness of the actual hat material.
My chosen rotors did need some modification: The centerbores did need to be opened up to mate with the 2.680" centering boss on the allroad hub, which also has a radiused edge on the inside (meaning a small amount of additional material must be removed on the rotor, even after opening it up to 2.68", to accomodate that radius). The lug holes also needed to be opened up from 12 to 14mm (I used a step bit).
That last, revelatory discussion with Joe:
"
... I measured the rotor, and in an
ideal world, its centerline would be offset .05"
more towards the inboard side... and this is from
an under-hat measure of 1.61"-ish, which I believe is
fairly precise. And, the rotor face is 27mm thick.
Pardon the mix of imperial and metric.
This boils down to an ideal underhat measurement
of 41mm for this rotor, which has a face of 27mm.
(1.61"+.05", in mm)
Therefore, the ideal measurement from underhat
surface (hub surface) to centerline of braking
width is 27.5mm, with optimum braking width
around 30mm.
That should be my best guide for choosing rotors.
"
So, the idea here, is that there isn't an ideal "underhat" measurement, since the width of the braking surface is also important. So, what is really important is the width between the underside of the hat flange (which abuts the hub), and and an imaginary centerline drawn through the middle of the braking ring.
Let's say that the ideal braking ring is 30mm wide. Here, with the rotor laying flat on a table, the centerline for that ring is 15mm high. Since you're looking for an ideal centerline-to-underhat measurement of 27.5mm, then you'd want an overall, underhat measurement of 42.5mm high (from the table to the underside of the hat).
Here's another email I traded today with a guy named Paul, who was looking at the 220-421-11-12 rotor:
"I have measured the "-11-12" rotor as well, and
it is not the offset you need.
The 09-12 rotor is the one you need. It measures
roughly 1.61" under the hat. The height to the
top of the hat is 1.845, and the flange is .230
thick. Braking ring is 1.190" thick.
220-421-11-12 measures almost double that, which
is 3.00 to the top of the hat, and a .243 thick
hat. The braking ring width is 1.262, or quick
mental math, around 30mm (1"=25.4mm).
The 09-12 rotor corresponds to 2002-2004 AMG C32,
and 05-06 C55 AMG.
I hope this helps,
Bob
"
Typing this out means I should finally list my findings of other, 345mm-diameter rotors that I found. I will list part numbers if I have them.
Measurement legend:
ML55 rotors, 2000-2003:
31mm thick braking surface
Overall height: 2.050
Flange thickness: .275
ML430 (I think this is the 2000-2005 stretch), 30mm thick braking surface:
Overall height: 2.060
Flange thickness: .275
Toureg, the 345-ishmm rotor version (there may be many braking versions on this vehicle, not sure):
350mm diameter, 34mm braking width (which may be too wide for the cayenne calipers!)
Overall height: 2.750
Flange thickness: .350
Now, remember, all of the above are 5 lugs, but are not 112.5 (or whatever the allroad dimension is). They are all larger, but that's ok - since they are 5 lug, they can either be redrilled just out of phase (virgin holes) or otherwise adapted. It's not a dealbreaker.
S8 rotor, 2001 (which I believe is around 31mm):
Overall height: 2.395
Flange thickness: .295
I believe this next set of measurements is from a B6S4. This is from a frantic scribble of notes I transcribed from my phone that I made last time I had it in for service. I honestly am not sure, but I believe it is the B6S4, since I recall that as being JUST too shallow of a rotor.
Overall height: 46mm
Flange thickness: 8mm
One rotor I never checked was the S500 Armored Body, 2004-2006, 30mm braking width. It's MB part number 220 421 19 12, and the rotors are US$900 or something each - needless to say, I did not order these "just to try them."
I think there are other rotors as well. I detailed the discovery process in another post, btw. I did not look at any 6 lug rotors, and I may have even limited my search to just a few marques.... I honestly don't recall all criteria of my search.
But, as a capstone to this bloviation, here are all of my links:
<a href="https://forums.audiworld.com/allroad/msgs/201746.phtml">Overall details and information on fasteners I chose</a>
<a href="https://forums.audiworld.com/allroad/msgs/201215.phtml">Initial impressions as a passenger and recollections on MB Part numbers</a>
<a href="https://forums.audiworld.com/allroad/msgs/200907.phtml">Initial impressions as a driver</a>
<a href="https://forums.audiworld.com/allroad/msgs/200159.phtml">Quick statement of part number and quick explanation of measurement used</a>
<a href="https://forums.audiworld.com/allroad/msgs/200011.phtml">Teaser pic, Quick explanation of machining required, Brakeline mention</a>
<a href="https://forums.audiworld.com/rockymtn/msgs/97900.phtml">How I found all of these candidates (methodology on discovery and first hand measurement)</a>
This is great - I can now throw away like 8 pieces of paper.
The following users liked this post:
johanbrandon (02-01-2024)
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08-11-2007, 09:15 PM
#10
AudiWorld Super User
Thread Starter
Yeah, sorry for the detail....
Yes, it's wordy. Yes, it has a truly stunning amount of detail, "stunning" being used here not really as a complement. But, again, I can't believe that this hasn't been documented before, and I provide all of the info I know to allow people to make the best decisions. Um, srsly, maybe I did also go a bit overboard.
For those interested in the hard-and-fast how-to, there is one post I made that was very kit-like, BTW.
Bottom line - I LOVE tech, and without delving into Myers-Briggs-esque descriptors, this type of project suits me perfectly, and this partially explains my, um, rationale for posting. Maybe, though, if I can lead by example, more people will try stuff like this. I'd love to see more of this type info and tech on AW, AZ, wherever.
For those interested in the hard-and-fast how-to, there is one post I made that was very kit-like, BTW.
Bottom line - I LOVE tech, and without delving into Myers-Briggs-esque descriptors, this type of project suits me perfectly, and this partially explains my, um, rationale for posting. Maybe, though, if I can lead by example, more people will try stuff like this. I'd love to see more of this type info and tech on AW, AZ, wherever.