Girodisc rotors finally installed
Nordschleife Master
Joined: Oct 2003
Posts: 5,225
Likes: 32
From: Tobacco Road, NC
Makes sense. I'm just curious of the actual SURFACE AREA of the two rotors. While the giro has a radius of 11.5 mm more I'd still like to know if the area is larger and by how much. Still don't understand why they can't make a stock replacement that would not need the spacers.
Nordschleife Master
Joined: Oct 2006
Posts: 7,446
Likes: 69
Makes sense. I'm just curious of the actual SURFACE AREA of the two rotors. While the giro has a radius of 11.5 mm more I'd still like to know if the area is larger and by how much. Still don't understand why they can't make a stock replacement that would not need the spacers.
If you look at the diameter of both top hats... they are both the same. This diameter is needed to fit in the hub/axle. Now add the extra space needed for the mounting bolts for the disk... that where the extra 11.5mm is lost. Thats why it needs the 12mm spacer for the calipers. They cant make those disc mounting points inside the hats cause that area needs to be empty for the axle/hub... does that make sense?
Nordschleife Master
Joined: Oct 2003
Posts: 5,225
Likes: 32
From: Tobacco Road, NC
If that picture is to scale, then the measurements I just took are the same as well. So, back to my original question....
If the surface area of the two rotors is identical, then how is braking heat dissipation better? What about actual stopping power?
Trying to understand how these are better at $2200 versus $540 for stock at all 4 corners?
If the surface area of the two rotors is identical, then how is braking heat dissipation better? What about actual stopping power?
Trying to understand how these are better at $2200 versus $540 for stock at all 4 corners?
Nordschleife Master
Joined: Oct 2006
Posts: 7,446
Likes: 69
thats why I put heat dissipation, and fade in ??? in my statement. Weight is clearly an advantage and maybe my torque comment is true as well. If the replacement disc are cheaper than stock... that is another advantage.
Thread Starter
Rennlist Member
Joined: Jan 2008
Posts: 946
Likes: 202
From: London
The weights are in the original post, the larger disc has more surface area as the larger radius means a larger surface area even though the contact 'width' doesn't change...
Therefore increased surface area = increasing cooling = less fade
Also, decrease in unsprung weight. The Girodisc front discs offer a 18% improvement in surface area-to-weight for the rotor.
And, increased braking:
Torque = Force x Distance, brake torque is equal to the retarding force provided by friction between the pads and discs, multiplied by the radius of the contact point between the pad and disc. The increased diameter provides a larger effective radius, or torque arm the pads act upon, giving more braking force for the same system pressure...
The materials used also allow for greater heat dispersion, more carbon apparently...
Therefore increased surface area = increasing cooling = less fade
Also, decrease in unsprung weight. The Girodisc front discs offer a 18% improvement in surface area-to-weight for the rotor.
And, increased braking:
Torque = Force x Distance, brake torque is equal to the retarding force provided by friction between the pads and discs, multiplied by the radius of the contact point between the pad and disc. The increased diameter provides a larger effective radius, or torque arm the pads act upon, giving more braking force for the same system pressure...
The materials used also allow for greater heat dispersion, more carbon apparently...
Nordschleife Master
Joined: Oct 2003
Posts: 5,225
Likes: 32
From: Tobacco Road, NC
Dervish, did you weigh them before you installed them? Trying to figure out what the weights are before and after (both front and rear). Is the weight reduction you stated (9 to 7.8 kg) for just the fronts?
As far as suraface area, it wold be easy to get a number for both stock and these Giro's with simple calculations. I think this would be good info as well to have in this thread for people who do searches.
Devish, are these being used for track applications in your case?
As far as suraface area, it wold be easy to get a number for both stock and these Giro's with simple calculations. I think this would be good info as well to have in this thread for people who do searches.
Devish, are these being used for track applications in your case?
Rennlist Member
Joined: Jun 2005
Posts: 390
Likes: 3
From: Phoenix, AZ
I think that you gentlemen might be missing the fact that the overall diameter of the rotor is larger, even though the measured width of the pad surface at any given angle appears the same.
Imagine an 8-slice pizza that you add a 9th slice to. While the length of each slice on its cut is the same, the overall diameter grows larger and a circular hole appears in the middle of the pie.
So there's more swept rotor surface, which should aid in heat dissipation. I can't vouch for the overall performance of the rotors (and I'm no fan of the slotted look) but it's a fact that you're getting more rotor surface. 75% more in proportion to the added cost? Probably not. Dervish, I'm trying to understand your claim of a larger effective radius for the same contact area on the pad leading to more braking force. It's not that I don't believe you, it's more likely that I'm a poor mathematician.
Considering the stock braking performance built into every P-car to match its stock performance, this might be a solution for the driver who outbrakes their car on a consistent basis. I think that demographic is small. I track my car and I don't see fade in my rotors until the end of a few VERY hot runs, and even then it's progressive. Stock rotors, stock pads on a 997 C2S. I'm not the quickest car out there but I get along. My only complaint is dust and pad wear, which I'm compensating for with track pads this season.
Dervish: what part of your experience with the stock rotors led you to this purchase?
Imagine an 8-slice pizza that you add a 9th slice to. While the length of each slice on its cut is the same, the overall diameter grows larger and a circular hole appears in the middle of the pie.
So there's more swept rotor surface, which should aid in heat dissipation. I can't vouch for the overall performance of the rotors (and I'm no fan of the slotted look) but it's a fact that you're getting more rotor surface. 75% more in proportion to the added cost? Probably not. Dervish, I'm trying to understand your claim of a larger effective radius for the same contact area on the pad leading to more braking force. It's not that I don't believe you, it's more likely that I'm a poor mathematician.
Considering the stock braking performance built into every P-car to match its stock performance, this might be a solution for the driver who outbrakes their car on a consistent basis. I think that demographic is small. I track my car and I don't see fade in my rotors until the end of a few VERY hot runs, and even then it's progressive. Stock rotors, stock pads on a 997 C2S. I'm not the quickest car out there but I get along. My only complaint is dust and pad wear, which I'm compensating for with track pads this season.
Dervish: what part of your experience with the stock rotors led you to this purchase?
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Nordschleife Master
Joined: Oct 2003
Posts: 5,225
Likes: 32
From: Tobacco Road, NC
Not missing that at all. This is why I asked for the inner opening sizes. We can figure this out very easily. Calculate the area of the ENTIRE rotor for both stock and Giro (we know this already) and SUBTRACT the area of the non rotor area. This will give us not only the exact swept rotor surface but the difference between the two.
First set of numbers (before getting the center section measured to subtract out):
Giro Area
F (140.53 sq in)
R (128.61 sq in)
Stock
F (122.7 sq in)
R (109.3 sq in)
Need the measurement (diameter) of the inner section to finish up
First set of numbers (before getting the center section measured to subtract out):
Giro Area
F (140.53 sq in)
R (128.61 sq in)
Stock
F (122.7 sq in)
R (109.3 sq in)
Need the measurement (diameter) of the inner section to finish up
Rennlist Member
Joined: Nov 2003
Posts: 1,008
Likes: 21
From: los angeles
do they make this rotor for turbo sized rotors F/R? what is the cost differential. I was looking at replacements and OEM still came out cheaper for my car unless this has changed.
I much rather have slotted than cross drilled rotors, especially for the track.
Oh, and agreed on the 12mm single piece spacer rather than washers.
I much rather have slotted than cross drilled rotors, especially for the track.
Oh, and agreed on the 12mm single piece spacer rather than washers.
Thread Starter
Rennlist Member
Joined: Jan 2008
Posts: 946
Likes: 202
From: London
Ok, allot of questions.
I do track the car but not excessively. Maybe about once a month, one next Saturday at quite a brake heavy track so will get a good comparison. I do get fade even with SRF fluid and GT3 cooling ducts at this event. Have another 'RS' trackday 2 weeks later then a long weekend at The Ring the following month.
I really wanted a reduction in unsprung weight, increased braking force and reduction in fade without the need to go heavier and '6pot', that's when you really start spending big $$$$.
Another added bonus is hopefully the elimination of the dreaded inner surface rust/corrosion. This has always been a big problem with stock rotors, time will tell on this one.
I also can't rule out aesthetics, I actually really love the slotted look, plus no more drilling out blocked holes or measuring cracks...
Now the manufacturer info... Check this link out http://www.cargraphic.de/sources/dow...rodisc-web.pdf
It shows stock weights and dimensions versus Girodisc.
'number9ine' Think of it like this - A force applied at a right angle to a lever multiplied by its distance from the lever's fulcrum (the length of the lever arm) is its torque. A force of three newtons applied two meters from the fulcrum, for example, exerts the same torque as a force of one newton applied six meters from the fulcrum.
Torque = Force (caliper piston) x distance (disc radius)
I also don't believe that Porsche put the best braking system on the cars from factory for ALL users. Just as they don't with suspension. Yes the stock brakes are amazing when used correctly for general street/fast road use but the moment you push them hard for prolonged periods you experience the flaws. Hence why you can upgrade GT3 brakes to Alcons etc, surely you'd expect GT3s to have the ultimate brakes from factory?
Also have a look at this for all the manufacturer details... http://www.girodisc.com/catalog/prod...roducts_id=915
I do track the car but not excessively. Maybe about once a month, one next Saturday at quite a brake heavy track so will get a good comparison. I do get fade even with SRF fluid and GT3 cooling ducts at this event. Have another 'RS' trackday 2 weeks later then a long weekend at The Ring the following month.
I really wanted a reduction in unsprung weight, increased braking force and reduction in fade without the need to go heavier and '6pot', that's when you really start spending big $$$$.
Another added bonus is hopefully the elimination of the dreaded inner surface rust/corrosion. This has always been a big problem with stock rotors, time will tell on this one.
I also can't rule out aesthetics, I actually really love the slotted look, plus no more drilling out blocked holes or measuring cracks...
Now the manufacturer info... Check this link out http://www.cargraphic.de/sources/dow...rodisc-web.pdf
It shows stock weights and dimensions versus Girodisc.
'number9ine' Think of it like this - A force applied at a right angle to a lever multiplied by its distance from the lever's fulcrum (the length of the lever arm) is its torque. A force of three newtons applied two meters from the fulcrum, for example, exerts the same torque as a force of one newton applied six meters from the fulcrum.
Torque = Force (caliper piston) x distance (disc radius)
I also don't believe that Porsche put the best braking system on the cars from factory for ALL users. Just as they don't with suspension. Yes the stock brakes are amazing when used correctly for general street/fast road use but the moment you push them hard for prolonged periods you experience the flaws. Hence why you can upgrade GT3 brakes to Alcons etc, surely you'd expect GT3s to have the ultimate brakes from factory?
Also have a look at this for all the manufacturer details... http://www.girodisc.com/catalog/prod...roducts_id=915
Drifting
Joined: May 2008
Posts: 2,727
Likes: 6
From: Cali
The weights are in the original post, the larger disc has more surface area as the larger radius means a larger surface area even though the contact 'width' doesn't change...
Therefore increased surface area = increasing cooling = less fade
Also, decrease in unsprung weight. The Girodisc front discs offer a 18% improvement in surface area-to-weight for the rotor.
And, increased braking:
Torque = Force x Distance, brake torque is equal to the retarding force provided by friction between the pads and discs, multiplied by the radius of the contact point between the pad and disc. The increased diameter provides a larger effective radius, or torque arm the pads act upon, giving more braking force for the same system pressure...
The materials used also allow for greater heat dispersion, more carbon apparently...
Therefore increased surface area = increasing cooling = less fade
Also, decrease in unsprung weight. The Girodisc front discs offer a 18% improvement in surface area-to-weight for the rotor.
And, increased braking:
Torque = Force x Distance, brake torque is equal to the retarding force provided by friction between the pads and discs, multiplied by the radius of the contact point between the pad and disc. The increased diameter provides a larger effective radius, or torque arm the pads act upon, giving more braking force for the same system pressure...
The materials used also allow for greater heat dispersion, more carbon apparently...
You get better braking by pushing the caliper out another 10mm, thereby achieving more leverage with the same sized calipers and pads.
Yes the cost is high at first, but keep in mind these rotors will last longer (almost twice as long) and when they need replacement, it's only $300/wheel to replace the rotor itself (the aluminum top hat gets re-used).
These rotors are handmade here in So Cal by RSS. A very good company, and a great facility.
Nordschleife Master
Joined: Oct 2003
Posts: 5,225
Likes: 32
From: Tobacco Road, NC
I'm still trying to understand the "why" of these at $2200 (4 times the cost of stock).
Heck, the PFC 2-piece setup is cheaper than Giro.
Sorry, but I am not understanding the rationale for buying these. The braking system on these cars is phenomenal. And if you are boiling SRF (which I highly doubt) then there is something else at play. The proper brake cooling (cup ducts not the GT3 ducts and maybe even some ducting for additional airflow) and you will be just fine. And at Only $300 for a complete set of front replacements, you will need to go through a lot of rotors to get a descent ROI.
In VERY HARD braking situations I've used many different rotors, pads, fluid, etc in all the various 996 variants and this one doesn't make sense to me.
Just my $.02
Heck, the PFC 2-piece setup is cheaper than Giro.
Sorry, but I am not understanding the rationale for buying these. The braking system on these cars is phenomenal. And if you are boiling SRF (which I highly doubt) then there is something else at play. The proper brake cooling (cup ducts not the GT3 ducts and maybe even some ducting for additional airflow) and you will be just fine. And at Only $300 for a complete set of front replacements, you will need to go through a lot of rotors to get a descent ROI.
In VERY HARD braking situations I've used many different rotors, pads, fluid, etc in all the various 996 variants and this one doesn't make sense to me.
Just my $.02