When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Here's a little more in depth analysis behind the reasoning of using this caliper.
From factory, the brake bias is set more forward such that in the event of a lock up, the fronts locks before the rears. Locking the rears first can cause the car to spin, so car manufacturers would prefer to avoid setting a car up in that manner. However, to maximize braking potential, you want to use all four tires to the limit, but with a setup that's biased to the front, there will still be braking performance left in the rear tires.
Weight transfer plays the biggest role in brake bias setup. For a car that has a high center of gravity, once you brake, a lot more of the weight transfers to the front wheels. The perfect example is a motorcycle doing a stoppie. A motorcycle has a much higher center of gravity than a car, so under braking, all the load goes to the single front wheel. Now, for the AMG GT, the static weight distribution is already rearward at 53% to the rears. That, combined with the low center of gravity thanks to the dry sump motor. carbon roof, etc, the amount of weight transferred to the front wheels will be much less. This is all taken into account when deciding to shift the brake bias rewards.
The comments above are correct, the piston sizing is smaller. From the information I have, the OEM caliper has piston sizes of 32/34/38 with a piston area of 56.9cm^2, different from what Racing Brake has mentioned. The reduction in piston area of the AP caliper in conjunction with the new high coefficient of friction Ferodo DS3.12 pads, will shift the oem brake bias of 64% forward, to 63% forward. The intentional shift of the bias rewards is to take advantage of the reduced weight transfer from a lowered car, rear wing, and unrealized potential from the factory bias.
So back to the reasoning behind using this AP caliper. First is the fact that it uses a much thicker pad, this will provide a good thermal barrier to prevent the brake fluid from boiling as well as allow for many more track days on the same set of pads. Second is the intentional shift in brake bias to use more of the rear axle under braking. Third is the cooling capacity of the caliper itself compared to the Brembo. And as a cherry on top, this caliper is a good amount lighter than the oem setup.
It's not 100% relevant to this conversation but the part about the tires is. Tires are non linear. If you load it with 10lbs, you may get 10lbs of lateral grip. But if you load it with 20lbs, you won't get 20lbs of lateral grip. But if you load it with 5lbs, you could get 5.5lbs of later grip. In a sense, the tire is more "efficient" when its not loaded as heavily. Under 1g braking, the front axle will be ~1050kg normal force on 275 width tires, the rear axle loading will be reduced from static at about ~590kg on 325 width tires. The rears will be more efficient given the normal load it has, but the front will be less efficient with the added load and reduced tread width relative to the rear. This is a more in depth reasoning as to why the rearward bias was intentional.
However, brake bias is a living thing, to be optimal, it has to keep changing. There isn't a perfect setting for a track, or even a specific corner. That's why you'll see f1 drivers constantly change the brake bias throughout a lap since it can depend on many factors, not limited to, the speed of the corner, the way a driver applies the brakes, the relative condition of the front and rear tires and the aero balance.
Just got my AP Racing CP9668 front calipers installed on my GTS. Works with OEM Iron rotors but I have the Girodisc replacements since they have directional vanes unlike the OEM rotors.
These calipers have stainless steel pistons and allow for a thick 25mm pad for better thermal performance and pad life. The common pad size give me much more options for both street and pad compounds. These calipers are also 3.7lbs lighter per side than the OEM Brembos. 1.3lbs per side saved with the rotors vs the OEM Irons.
Hello Ronac,
I am tracking my gts also and I am suffering the same brake issues as you had. Currently I am using PFC Discs and Endless MA45B Pads on the stock calipers and I have the cooling ducts upgrade from the GTR Pro/BS.
It works fine for a few laps on the Nordschleife but after 3 laps my brake is starting to fade.
I would love to do the same Brakeupgrade as you have done but the one question I have is why the Pad is not using the whole surface of the disc?
This looks strange to me.
Can you explain why you are not using a different disc thats fitting the pad size?
Thank you very much in advance for your answer and I appreciate your support!
The AP caliper is designed to be used with their specific pad shape with a certain pad height. The rotor you see on my car is the OEM sized rotor, which pairs with the OEM caliper which has a taller pad compared to the AP caliper. The reason the same rotor is retained is because the diameter and thickness is a perfect match for the AP caliper. This is nice for someone that wants to just install these AP calipers without the added cost of replacing rotors as well. I've been using the Ferodo DS3.12 compound and they're fantastic.
The AP caliper is designed to be used with their specific pad shape with a certain pad height. The rotor you see on my car is the OEM sized rotor, which pairs with the OEM caliper which has a taller pad compared to the AP caliper. The reason the same rotor is retained is because the diameter and thickness is a perfect match for the AP caliper. This is nice for someone that wants to just install these AP calipers without the added cost of replacing rotors as well. I've been using the Ferodo DS3.12 compound and they're fantastic.
Thank you very much for your quick response! That track looks great and great driving!
Just from my experience I would recommend to find a brake discs that fits the size of your brakepads because of the heat extend on the disc.
The discs are designed to be used on the whole surfice. If you have hot and cold spots it's not ideal. but thats just my opinion
I will try to get the same brake upgrade as you under the circumstance that I can get a disc that matches the caliper and pad at the same time.
Do you know if I can get the adapters for the calipers seperately? I have the Calipers left from my old car thats why I am asking
If youre interested I have a nice onboard of a Nordschleife lap with my gts.
05-31-2020, 01:13 PM
