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VW vs Audi Brake Rotors

MarkP888

Passed Driver's Ed
Location
Lancaster, PA USA
Car(s)
2015 VW GTI
I have zimmerman rotors from FCP euro and still get rust. They say their coated to prevent rust, but I still get rust when it rains or I'm washing the car.
Goes away once I drive the car and brake.
I think high-quality rotors like Zimmerman likely have a bit less iron and/or a bit more chromium (or whatever they use to balance the other metals) so that although they rust on the braking surfaces, it isn't as severe as less expensive rotors (like I have on the VW). The Audi (likely Zimmerman) rotors still get a thin coating of rust if they sit out in the rain, cold, but it cleans off with a very short period of braking. Very different from the VW rotors I have which basically never come clean, even after significant braking.
 

bentin

Autocross Champion
Location
Austin, TX
Car(s)
18 GTI SE - 3 Pedals
It's the pads. GTI pads have more metallic content and dust like mad. Audi pads are low in metallic content and barely dust. You're seeing the pad material rust. Change to a metallic pad on the Audi and your rotors would look the same, or obviously, the opposite, run a less aggressive pad on the VW and you'll have less ugly rotors when it rains.
 

edsonmassao

Passed Driver's Ed
Location
Brazil
Car(s)
2017 GTI DSG
It's the pads. GTI pads have more metallic content and dust like mad. Audi pads are low in metallic content and barely dust. You're seeing the pad material rust. Change to a metallic pad on the Audi and your rotors would look the same, or obviously, the opposite, run a less aggressive pad on the VW and you'll have less ugly rotors when it rains.
Should pads with more metallic content offer more stopping power? If they are much better I think I could live with the rust...
 

bentin

Autocross Champion
Location
Austin, TX
Car(s)
18 GTI SE - 3 Pedals
Should pads with more metallic content offer more stopping power? If they are much better I think I could live with the rust...
Yeah, at the expense of brake dust and rotor wear. The stock VW pads certainly aren't as aggressive as things get, but for a street car, they're pretty good. The same is not true of the Audi pads, even with good tires, those things take forever to stop. But they'll have clean rims, so most owners are happy.
 

dequardo

Autocross Newbie
Location
America’s Dairyland
Car(s)
‘21 GLI Autobahn GLI
It’s simply rotor quality. Wife’s Equinoxes (now on number 4) never rust in the rain.
 

MarkP888

Passed Driver's Ed
Location
Lancaster, PA USA
Car(s)
2015 VW GTI
It's the pads. GTI pads have more metallic content and dust like mad. Audi pads are low in metallic content and barely dust. You're seeing the pad material rust. Change to a metallic pad on the Audi and your rotors would look the same, or obviously, the opposite, run a less aggressive pad on the VW and you'll have less ugly rotors when it rains.
You sir are right on the money.

I was also able to confirm that the front rotors on the GTI are the original OEM rotors. I was able to get a photo showing the part number to be 5C0615301B, which appears to be an ATE coated rotor made for VW.

20220802_192614.jpg


Screenshot_20220802-192547_Chrome.jpg
 

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evilhomura89

Passed Driver's Ed
Location
SEA
I'm using brembo OEM rotors (09.9772.11 front 312mm ventilated and 08.C501.11 rear 300mm solid) on my mk7 GTI - they rust after washing/rain as well.

Since we're discussing rotors here, does anyone know if it's normal to have brake pad marks on the rotor?
My rear rotors have plenty of those pad marks - personally I believe it's due to the EPB/auto hold function that cause pad material to transfer unevenly when it's running hot. I'm using ATE ceramic pads currently.
 

bentin

Autocross Champion
Location
Austin, TX
Car(s)
18 GTI SE - 3 Pedals
It’s simply rotor quality. Wife’s Equinoxes (now on number 4) never rust in the rain.
Again, it’s pad composition. The rust is metallic pad compound. If you don’t run metallic pads, little to no surface rust.

I run the exact same rotors on two bikes, one is a casual, ride with the kid single speed with organic pads and the rotors never rust. The other is an all mountain bike with downhill metallic pads. Those rotors are pretty much orange unless you’re actively riding it. Same rotors, different pads.

Porsche even has an option specifically for low dust.

http://www.safebraking.com/tech-porsches-white-brake-calipers/
 

tigeo

Autocross Champion
The rain brake drying setting should be set to work from factory...no need to turn it on. You can just check in the brake module adaptations. It works by pulsing the brakes when the wipers are on at some interval. The rust has nothing to do with that.
 

tigeo

Autocross Champion

tigeo

Autocross Champion

MarkP888

Passed Driver's Ed
Location
Lancaster, PA USA
Car(s)
2015 VW GTI
I have zimmerman rotors from FCP euro and still get rust. They say their coated to prevent rust, but I still get rust when it rains or I'm washing the car.
Goes away once I drive the car and brake.
I assume they are not rusting on the non-braking portions of the rotor though, correct?

Here is the OEM rotor after driving about 20 miles this am in stop-and-go traffic with plenty of longer stops to clean the rotors. This is as good as they get. I plan to replace the rear rotors and pads soon-ish.
20220803_103849.jpg
 
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