Planet 9

**Craig@Rennstore.com** · #1 02-16-2009, 01:18 PM

Feb 16th 2009:

The logiocal extension of carrying the best brake pads for the Porsche lineup - www.RennStore.com -- The source for Pagid brake pads now carries Girodiscs!

Yes, these are absolutely *the* solution for the holed OEM rotors which crack and form deep grooves with track use -

The Girodiscs offer increased rotor mass, ie thermal reserves, which in turn puts less stress on the brake fluids and pads - and less stress on the calipers too!

E-mail me at: Rennstore@comcast.net

**JCay** · #2 02-16-2009, 01:51 PM

Wait... so these are heavier than stock?

**Craig@Rennstore.com** · #3 02-16-2009, 02:24 PM

Factory Front: 18.6 lbs
Girodisc Front: 17.2 lbs
Factory Rear: 13.6 lbs
Girodisc Rear: 14.8 lbs

Front swap = -1.4lbs per disc or -2.8lbs total
Rear swap = + 1.2lbs per disc or +2.4lbs total

Net = -.4lbs so about a 1/2 of a pound in unsprung weight reduction overall.
~~~~~~~~~
The GiroDisc rotors are LARGER than OEM. You can't lose with this combination.

trebien · #4 02-16-2009, 05:49 PM

Originally Posted by Craig@Rennstore.com

The Girodiscs offer increased rotor mass, ie thermal reserves, which in turn puts less stress on the brake fluids and pads - and less stress on the calipers too!

So they have increased mass... and weigh less.

I see...

**Craig@Rennstore.com** · #5 02-16-2009, 06:27 PM

It's the new law of physics, you haven't had that lesson yet?

The mass is in the radial direction, easier to dissipate the heat up front.

**jaica** · #6 02-16-2009, 06:43 PM

+1 on Girodisc. I am sure there are better setups, but a what price? I am very happy with mine. I can outbreak just about anything (normal cars, I have not checked it against 2000# cars)at the track. Good modulation and feel, More than enough for me. I find them easier to be gentle at the start, and firm at the same time.

Note the tracks here are not that long, top speeds 130 in normally aspirated cars, turbos and 500hp cars can reach 140 to 145.

**Craig@Rennstore.com** · #7 02-16-2009, 09:07 PM

I'm a track rat, and for me the biggest benefit is the longevity and resistance to the plague of cracks and deep grooving common to the OEM rotors - when these cars see track days.

When it's time for replacement rotors, these have got to be on the short list of consideration -

trebien · #8 02-17-2009, 04:44 PM

Originally Posted by Craig@Rennstore.com

It's the new law of physics, you haven't had that lesson yet?

The mass is in the radial direction, easier to dissipate the heat up front.

Not if it's "new" physics. Since last time I took a physics class was over a decade ago, during my aerospace engineering education at an ivy league school.

I can understand increased cooling due to better vane design, materials & construction, etc. But I was just wondering how a 2 pound lighter rotor (fronts) can have increased thermal mass, unless the specific heat capacity of the lighter rotor's material has significantly increased.

**jaica** · #9 02-17-2009, 05:21 PM

I was at engineering school a couple of years ahead of you, so pardon me if I wonder off.

The Girodisc rotors have a lot less mass at the hats and more mass at the rotor part. As a result they have a lot more mass in the heat generating/dissipating area than OEM rotors. They also have a higher second moment of inertia( not good), but that is a cheap price to pay for great stopping power, longer rotor life , better modulation. Remember a car that does not go its a problem, a car that does not stop is a bigggggg problem.

**Craig@Rennstore.com** · #10 02-17-2009, 05:47 PM

The aluminum hats do indeed make the weight difference - ie aluminum centers.

The thermal mass increase is in the disc area itself -

For me the biggest benefit is the sheer quality of the material itself, the inherent resistance to cracks and grooving, and the aforementioned mass in the rotor face area.

Go to a LeMans, Sebring, or a Daytona 24 hr race and you will notice NO ONE uses holed rotors. Track use deserves something better than the old Porsche holed rotors.

**Craig@Rennstore.com** · #11 02-17-2009, 05:52 PM

My rotors after 5 track days - unacceptable - in 5 more track days after this picture, the cracks were incredible -

trebien · #12 02-17-2009, 09:04 PM

Originally Posted by jaica

The Girodisc rotors have a lot less mass at the hats and more mass at the rotor part. As a result they have a lot more mass in the heat generating/dissipating area than OEM rotors.

How much more?

I understand the underlying principle, but I wonder if this has actually been measured. What is the actual thermal mass of the original rotor compared to a GD rotor? Not in theory, but in the real world. What is the actual thermal "inertia" of the 2 rotors, comparitively.

We know the front brakes do most of the work, and the GD rotors weigh almost 1.5 pounds less each. I wonder how much of that is actually due to the hat.

I have years in the performance industry and question unsubstantiated claims. So I'm just curious what the real numbers are... that's all.

**Seamus** · #13 02-18-2009, 04:05 PM

If the pads/calipers are no larger, how do "larger" discs matter?

**Craig@Rennstore.com** · #14 02-18-2009, 05:14 PM

Leverage and heat sink capability.

As a side note, the GiroDiscs disc replacement entails the rotor and hardware and keeping the hat in most cases. Savings there.

girodisc martin · #15 02-18-2009, 06:53 PM

Just to quickly provide an answer to the weight issue...

I did a quick 3D solid model of the factory iron rotor "hat section" and calculated the volume and density to get a rough weight. This should be very close to actual. 3.8-4.0 pounds for the stock "rotor hat" (If anyone wants to smash theirs out and give me the weight of the pieces that could be fun!) 18.6-3.8 is 14.8 lbs for the rotor ring portion only. Our rotor ring weighs 15.65 pounds. Approx 1 lb more iron mass. Hat and hardware came to roughly 1.5 lbs. This is really splitting hairs however. The main benefit behind this was to have slotted rotors for the track, a 2-piece floating design to keep the rotors flat at extreme temps, and have something that filled the wheels a bit more both for a longer lever arm and for looks. We also use a different grade iron that wears a bit longer with aggressive pads. These rotors are starting their third season in Grand Am on GS cars, proving themselves, both in their cooling and longevity.

If I can answer more questions I will!

Thanks,

Martin

**Craig@Rennstore.com** · #16 02-20-2009, 12:44 PM

Replacement rotors for that time when the GiroDisc discs themselves need renewed?

Cost is about HALF the entire setup price, in the ballpark of OEM rotor cost and a heck of a lot better -