Brakes are important on any car, and a heavy/powerful car (like the V8 Mustangs) needs a bit more attention in this area. For motorsports use, other than autocrossing and drag racing, the performance of the brake system is even more critical. For our typical customers - HPDE/TT/W2W racers - the brakes can be the difference between winning and crashing.
Left: Autocross speeds don't tax the brakes all the much. Right: But road course sure does!
Ford is not known for installing "overkill" brakes on a lot of these cars over the decades, especially the Fox/SN95 models like the one below. But thankfully, Ford does have a good ABS programming scheme.
The needs of a braking system are somewhat simple: have enough brake torque to match the speeds/weight/power of a given car, with a well supported brake pad (caliper design) and adequate cooling to keep the rotor, pad, and caliper from overheating with continue track use.
Most factory brake setups are underwhelming in some aspect listed above. Either the pads are crap, the factory hydraulic fluid boils easily, or the rotors are sized poorly and do not give good brake torque. Normally it comes down to managing heat - once the rotors reach a critical temperature, the friction generated by the brake pads falls off to nothing. Or the hydraulic fluid boils and the system quickly loses clamping power.
Sometimes the caliper or rotor design is compromised, normally due to costs. We will discuss the challenges on the various S550 Mustang brakes starting below.
THE S550 BRAKE SYSTEM CHALLENGES
If you follow our S550 Build Thread you know that we have had a lot of "fun" chasing some issues with the factory brakes on our 2018 GT - which had the Base Model GT brakes, which are very different than the Performance Pack 6-piston 15" front brakes.
The 2015-19+ Mustangs come with a somewhat underwhelming and bizzarre brake rotor design.
These are the front (left) and rear (right) brakes that come on the 2015-up S550 base model GT and some Ecoboost Mustangs
The 2015+ S550 Mustang Ecoboost and base model GT 2015+ base model GTs have some sizable 4 piston fixed calipers and 14" diameter rotors, comparable in size to the 14" Brembos on the S197 Mustangs cars. The S550 rear rotors are well sized also with a single piston slider rear caliper.
The 2015-18 S550 Mustang front 14" rotor (above left) got heavier than the S197 14" front rotors (above right) by about 3 pounds. And usually more rotor weight means more heat capacity / thermal mass, since a brake systems' ability to absorb and shed heat is somewhat related to rotor mass. But there is one fatal flaw in the rotor design that tanks the S550 version.
This is the "inverted hat" rotor design, and it cannot cool with any continued abuse or road course use. If you look above at these 14" front rotors, notice that the cooling vanes are on the outside. This means we cannot add any sort of forced air brake cooling to these rotors, and there is no natural airflow from under the car out through the brakes. These are essentially backwards from traditional rotor design.
The above picture shows this inverted hat rotor from the back side - which is 100% sealed off from airflow. This means we cannot add any brake cooling via normal ducting, where we force air into the back side of the rotor, which can then flow through the rotor vanes to remove heat. With no physical way to force feed air through the back of the rotor face and through the vented rotor section, we cannot cool these down. Ever. They will eventually get so hot that they stop stopping. Which is exactly what we are seeing in track use.
I ran these stock 14" brakes with the brand new factory pads and the teenie tiny 235mm wide base GT mud and snow rated tires and they lasted 8 laps on a "brake easy" track, in our first track test # 1. EIGHT LAPS. After the 7th laps in that first test session they were no longer capable of stopping the car at even my mild .85 g stops. I almost went off track, so I came in. The (Motul RBF600) fluid we had in there never boiled, I never had a "soft pedal", the damn car just wouldn't stop anymore.
We looked at the brand new stock front brake pads soon after this first track test and noticed that all of the pad material was gone... just a sliver of pad left, with 300 street miles, one autocross, and 8 laps at MSR-Cresson. Those handful of laps on course KILLED otherwise brand new pads. After this test we installed new G-LOC R8 track worthy front brake pads + R8 rear pads.
At this event we had also installed coilovers, 19x11" wheels, 305mm wide RE-71R tires and camber plates. We found 9 seconds of lap time from our first test, but now the brakes were even less up to the task of rack use. The brakes didn't get worse, rather the car just got a lot faster. The same thermal limitations of the inverted hat rotors showed up sooner - due to the faster lap times the car was capable of.
Above is a g-trace from our AiM data logger from this second event, with the R8 compound track pads on the 14" 4 piston base brakes. The max g-forces logged over a 3 lap session was 1.02g stopping. Lateral grip on the RE-71R tires was 1.2g sustained with 1.34g spikes. Braking was limited to about .90g stops, otherwise it would overheat the rotors/pads in one stop. As the g-trace shows, the brakes could spike to 1.0g, but only about once every lap, for one good stop.
In the video linked above, we interview Marco Garcia, the former Ford engineer who worked on both the NVH and Vehicle Dynamics teams prior to the launch of the S550 Mustang. In this 25 minute interview with an "inside man" during the S550 Mustang's development, we discuss the track capabilities, challenges and potential fixes for the brakes on the S550 chassis. Lots of technical info, and some behind the scenes info, about the 2015-up Mustang with comparisons to the previous generation S197. We talk about brakes - a lot - so hopefully you will hear something useful.
continued below
Left: Autocross speeds don't tax the brakes all the much. Right: But road course sure does!
Ford is not known for installing "overkill" brakes on a lot of these cars over the decades, especially the Fox/SN95 models like the one below. But thankfully, Ford does have a good ABS programming scheme.
The needs of a braking system are somewhat simple: have enough brake torque to match the speeds/weight/power of a given car, with a well supported brake pad (caliper design) and adequate cooling to keep the rotor, pad, and caliper from overheating with continue track use.
Most factory brake setups are underwhelming in some aspect listed above. Either the pads are crap, the factory hydraulic fluid boils easily, or the rotors are sized poorly and do not give good brake torque. Normally it comes down to managing heat - once the rotors reach a critical temperature, the friction generated by the brake pads falls off to nothing. Or the hydraulic fluid boils and the system quickly loses clamping power.
Sometimes the caliper or rotor design is compromised, normally due to costs. We will discuss the challenges on the various S550 Mustang brakes starting below.
THE S550 BRAKE SYSTEM CHALLENGES
If you follow our S550 Build Thread you know that we have had a lot of "fun" chasing some issues with the factory brakes on our 2018 GT - which had the Base Model GT brakes, which are very different than the Performance Pack 6-piston 15" front brakes.
The 2015-19+ Mustangs come with a somewhat underwhelming and bizzarre brake rotor design.
These are the front (left) and rear (right) brakes that come on the 2015-up S550 base model GT and some Ecoboost Mustangs
The 2015+ S550 Mustang Ecoboost and base model GT 2015+ base model GTs have some sizable 4 piston fixed calipers and 14" diameter rotors, comparable in size to the 14" Brembos on the S197 Mustangs cars. The S550 rear rotors are well sized also with a single piston slider rear caliper.
The 2015-18 S550 Mustang front 14" rotor (above left) got heavier than the S197 14" front rotors (above right) by about 3 pounds. And usually more rotor weight means more heat capacity / thermal mass, since a brake systems' ability to absorb and shed heat is somewhat related to rotor mass. But there is one fatal flaw in the rotor design that tanks the S550 version.
This is the "inverted hat" rotor design, and it cannot cool with any continued abuse or road course use. If you look above at these 14" front rotors, notice that the cooling vanes are on the outside. This means we cannot add any sort of forced air brake cooling to these rotors, and there is no natural airflow from under the car out through the brakes. These are essentially backwards from traditional rotor design.
The above picture shows this inverted hat rotor from the back side - which is 100% sealed off from airflow. This means we cannot add any brake cooling via normal ducting, where we force air into the back side of the rotor, which can then flow through the rotor vanes to remove heat. With no physical way to force feed air through the back of the rotor face and through the vented rotor section, we cannot cool these down. Ever. They will eventually get so hot that they stop stopping. Which is exactly what we are seeing in track use.
I ran these stock 14" brakes with the brand new factory pads and the teenie tiny 235mm wide base GT mud and snow rated tires and they lasted 8 laps on a "brake easy" track, in our first track test # 1. EIGHT LAPS. After the 7th laps in that first test session they were no longer capable of stopping the car at even my mild .85 g stops. I almost went off track, so I came in. The (Motul RBF600) fluid we had in there never boiled, I never had a "soft pedal", the damn car just wouldn't stop anymore.
We looked at the brand new stock front brake pads soon after this first track test and noticed that all of the pad material was gone... just a sliver of pad left, with 300 street miles, one autocross, and 8 laps at MSR-Cresson. Those handful of laps on course KILLED otherwise brand new pads. After this test we installed new G-LOC R8 track worthy front brake pads + R8 rear pads.
At this event we had also installed coilovers, 19x11" wheels, 305mm wide RE-71R tires and camber plates. We found 9 seconds of lap time from our first test, but now the brakes were even less up to the task of rack use. The brakes didn't get worse, rather the car just got a lot faster. The same thermal limitations of the inverted hat rotors showed up sooner - due to the faster lap times the car was capable of.
Above is a g-trace from our AiM data logger from this second event, with the R8 compound track pads on the 14" 4 piston base brakes. The max g-forces logged over a 3 lap session was 1.02g stopping. Lateral grip on the RE-71R tires was 1.2g sustained with 1.34g spikes. Braking was limited to about .90g stops, otherwise it would overheat the rotors/pads in one stop. As the g-trace shows, the brakes could spike to 1.0g, but only about once every lap, for one good stop.
In the video linked above, we interview Marco Garcia, the former Ford engineer who worked on both the NVH and Vehicle Dynamics teams prior to the launch of the S550 Mustang. In this 25 minute interview with an "inside man" during the S550 Mustang's development, we discuss the track capabilities, challenges and potential fixes for the brakes on the S550 chassis. Lots of technical info, and some behind the scenes info, about the 2015-up Mustang with comparisons to the previous generation S197. We talk about brakes - a lot - so hopefully you will hear something useful.
continued below
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