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Unread 04-03-2019, 12:04 PM
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Default Mustang S550 Brakes - Uses, Limitaitons and Upgrade Options

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

Last edited by Fair!; 04-04-2019 at 04:03 PM.
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Unread 04-03-2019, 02:01 PM
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Default Re: Mustang S550 Brakes - Uses, Limitaitons and Upgrade Options

continued from above

When people challenge our data and first hand experiences with the 14" S550 brakes, we usually have to get into a big online argument - over who is driving fast enough to "use up" these brakes, and who is driving at parade lap speeds. As with anything that heats up over use, there are ways to "never overheat" these brakes, but it involves driving slowly and/or braking very gently. That proves nothing...



The folks that are capable of making the S550 14" brakes last are compensating for this obvious, verifiable disadvantage in this brake design. Every time someone chimes up that their S550 14" brakes are working, it turns out that their lap times explain their ability to "make these brakes work". Even racers who claim this brake system works - ask to see their results. Likely they will be 18th out of 23 in class - the bottom 5th of a class of similar cars. Results matter.

WHEN ARE THE 14" S550 BRAKES APPROPRIATE?

We feel that the S550's 4 piston 14" brakes are only appropriate for a handful of end users and situations in an S550 Mustang. Here are some examples of where they might make sense and their potential downsides.

1. For an absolute beginner HPDE drivers starting out that already have these brakes on their cars. We always caution against wanton spending by HPDE beginners before their first events. This assumes they will have some in-car supervision (instructor) to watch for signs of brake fade and warn them of what to do if they start to lose the brakes.



2. For the casual HPDE track drivers on an extreme budget, who aren’t worried about pushing their lap times and are willing to sit out a session or two to cool off. Something like the SCCA TNiA / low pressure "fun" events. But, running laps at 80% of the car's potential and missing sessions can get boring.

3. Some W2W race classes used to limit brake upgrades on some cars beyond the base model/stock bits, or have a hard 14" max diameter limit. The pre-2016 NASA PT rules used to add "classing points" for anything beyond base model brake calipers/rotors, and NASA American Iron series up through 2018 only allowed a maximum of 14” diameter rotors. But the newer NASA ST rules where the Mustang fits allow any brakes, and starting in 2019 the AI rules changed to allow up to 15” rotors. So now there are no longer any rule restrictions in the typical racing classes (see below). This was due to S550 Mustang racers in AI who were restricted from even using the optional Performance Pack 15" 6 piston brakes.



4. Autocrossers can use the 14" brakes, or even the slider calipers that come on the base model Ecoboost. The weight savings over the 15" brake are real, and they are unlikely to overheat. With a good pad, they are appropriate. And it is hard to overheat any brake system in a 30-60 second autocross run at parking lot speeds.


The base S550 14" rotor (left) is 5.7 pounds lighter per side than the optional Performance Pack 15" S550 rotor (right)

That is a limited list of uses where it's appropriate to keep the 14" S550 brakes. Its still very questionable, and will never be worthwhile on track, but we wanted to make that list to be fair.

WHEN IS IT TIME TO UPGRADE TO THE 15" S550 PERFORMANCE PACK BRAKES?

At what point should an S550 Mustang, that started with these restrictive 14" brakes, upgrade to the the 15” brakes?



Any time you want trouble-free, easy to use, inexpensive brakes. The Moderate to Advanced HPDE drivers, who are pushing the car and trying to develop skills, usually without an instructor in the car. Or if you don’t want to have to juggle the issues with the car and the brakes need to just “work” all the time so you have an environment to work on driving. The 6 piston Brembo calipers have larger pad but are actually lighter than the 4 piston base S550 calipers, as seen above.

The larger diameter, properly cooled 15" Brembo brakes that came on the Performance Pack models from 2015-up work considerably better. These brakes cut down on consumable costs, and can be used with a milder pad compound.



Wheel to Wheel Racers and Time Trial competitors on a budget should run the 15" brakes. This way they will not have to use the highest heat compound brake fluid with more frequent flushing intervals, and more expensive/highest heat range brake pad compounds. The cooler brakes will allow the pads, rotors, and hubs to have a longer service life.



Competitive track drivers who can benefit from shorter brake distances, and lower lap times. Better brake modulation can be had with less aggressive pad compounds, and cooler brakes that can be used for longer races and track sessions.

WHAT IS THE BRAKE UPGRADE PATH FOR THE S550?

In final testing some smart engineers at Ford realized how badly the 14" brakes performed on track so they made this 15" 6-piston Brembo brake design, which has traditional rotor construction and can be cooled passively or with ducted hoses. Sadly less than 7% of S550 Mustangs produced get this option so 93% of the cars built are equipped with less-than-ideal brakes.

We made this upgrade to our 2018 GT that came with the smaller 14" brakes, hoping for a big improvement in stopping power and longevity on track. And it worked great, after we also upgraded the brake hydraulics to the correct Performance Pack brake master cylinder unit (as Ford intended).



Since our aftermarket BBK option (Powerbrake) is costlier than many HPDE folks can afford, we added our version of the S550 15" 6-piston Brembo brakes, with all new Ford parts. PLUS we added the much needed master cylinder, all priced below most listings for the same kit without the master cylinder. Its a relatively cost effective upgrade that can ensure you still have working brakes after 20 minutes of track use.



The Vorshlag kit gives you everything needed to upgrade from the 14" base brakes to the larger and better cooled S550 15" brakes with new rotors, calipers, mounting hardware, caliper pins and shims, and a new Performance Pack master cylinder.



We also developed a ducted brake cooling kit for the 15" brakes in 2018, which we made production versions of in 2019. We have lots of upgraded brake pad options for the 14" and 15" brakes - and we can help you figure out what combination of pads will work for your end use.


G-traces from May 2018 NASA @ COTA event with 15" PP brakes

With our car upgraded to the 15" Brembo brakes, our brake cooling kit, and G-LOC brake pads we managed g-traces of 1.2g stops, lap after lap at COTA in May 2018. This was up from the 1.02g "one stop" performance on the 14" brakes with the same G-LOC pads before. This is over a 20% increase in stopping forces, plus the invaluable longevity. The lap time delta and measured data is there - its not hard to understand, but we are here to help if you want to know more.

WHAT BRAKE UPGRADE OPTIONS EXIST BEYOND THE 15" BREMBOS?



Of course there are aftermarket solutions with bigger calipers and 2-piece rotors to remove some of the weight gain from the PP brakes - like the Powerbrake 6 piston 15" kit, which is 21 pounds lighter than the S550 PP1 brakes, but costs do go up....



Late in 2018 we tested the first 380x34mm 6 piston Powerbrake X6EL big brake kit on our S550 test car. The braking improvements at COTA were real, as were the lap time drops.



We have been using these for many months on our car and did notice an improvement in stopping power. On the same COTA circuit the g-traces went from 1.2g on the 15" Brembo brakes to 1.4g stopping on the Powerbrake setup. Another 20% gain, which was kind of amazing. But the cost for this jump from the PP brakes is considerably more than the cost from base brakes to PP. Just another data point for people to think about.

Cheers,

Last edited by Fair!; 04-04-2019 at 04:24 PM.
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