Question about items in the performance package

[DivineStrike]

tbonez got the basics, I'll go into it further:

Large Brake Rotors: How these improve braking is counter-intuitive. The sole premise of brakes is to take kinetic energy and transmit it into heat energy and then dissipate it (ironically this is how your shocks/struts work too). Larger brake rotors increase brake torque which makes for a grabbier brake pedal (IE: more brake torque sooner) and it allows for more heat to enter the system before it overheats. More brake torque does NOT translate into shorter stopping distances because there is enough brake torque with smaller systems to cause ABS engagement. If you aren't familiar with what ABS does, the sensors detect when a wheel locks up and then it pulses the brakes to cause them to engage and disengage rapidly to bring the car to a controlled stop. In order for your wheels to lock up the amount of brake torque has to be high enough that the friction caused by the rolling tire on the roadway is overcome by the friction between the brake pads and the rotor. A 05-09 Mustang with 315 wide Hoosier A6 autocross slicks (arguably one of the stickiest tires in the world) will still hit ABS with stock pads, stock rotors and stock fluid without issues. What this tells us is that tiny 12.4" rotors on the 05-10 cars is MORE than plenty to handle locking up super wide and super sticky tires. IE: Adding brake torque will not stop the car quicker.

So that leaves us with slightly better initial bite with the brake pedal and a larger heat sink. A larger heat sink allows for more braking events before you either boil the brake fluid or fry the brake pads or warp the rotors. That's all that you gain from larger rotors.

The calipers, the 4 piston Brembo's for the EBPP and the 6 piston Brembo's for the GTPP offer better rigidity and a larger heat sink too. That rigidity translates to better pad wear and more consistent braking performance. Very important for track day guys looking to get the most out of the braking system in the car.

Good info mostly, except that a larger braking surface does allow for shorter stopping distances. Just because a 12.4 in braking surface can engage ABS doesn't mean it equals the same braking ability or stopping distance in a 15 in rotor. A 12.4 in rotor needs more hydraulic force to engage ABS. A 15 inch rotor requires less, which inherently also requires less time to build the pressure you need to engage ABS. Granted this amount of time isn't a lot but it can save you a couple feet, maybe more. I would have to do a comparison test to be sure.

With that said I believe the Mustang has a booster which senses how fast your pressing the brake pedal so it automatically increases pressure faster, minimizing this benefit even more. Can't remember the systems name. Ah hah, found it really simple name lol. It's called emergency brake assist

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[908ssp]

Actually actuating the ABS does mean the same torque is being supplied to the tire and it is slipping that slipping tell the ABS controller to release pressure on the caliper on the tire that is out of sync ie:slipping.

 

[JimmyTwoTimes]

The counterpoint to that, Jimmy, is that the non-preloaded helical gear differential is much easier to maneuver and steer on snowy and icy surfaces, since the clutch pack's preload tends to resist differentiation (and thus changing direction), and this is amplified on snow. I've had many clutch-type differential cars become unsteerable in winter. Combine that with the fact that helical gear diffs transfer torque much more progressively, whereas clutch-types become an all-or-none affair on low-mu surfaces, and you realize that the Torsen option is pretty good in the winter. The actual number of times that you have zero traction in the winter are pretty few, and frankly, with just a little help from the traction control the issue becomes entirely moot. I've spent a lot of time and have a lot of data on this topic. I also have Torsen diffs in both axles of my Mountaineer and flog it pretty harshly during winter rally season, so I've got some experience here...

I guess to clarify: my main concern is with being stuck in a snow bank and getting out of it, the type of situation where you need to rock back and forth to get out of it -- always happens to me three or four times a winter. Traction control and stability control needs to be shut off for that, and a locked diff is the best thing for it. Clutch LSD is second best.

 

[DivineStrike]

Actually actuating the ABS does mean the same torque is being supplied to the tire and it is slipping that slipping tell the ABS controller to release pressure on the caliper on the tire that is out of sync ie:slipping.

You missed my point entirely, and your point is included in my post. My point is the amount of hydraulic pressure required for that amount of force

 

[Whiskey11]

IIRC all models get the t-lock limited slip diff just like the '11+ S197 models. I haven't seen anything that says e-diff in the 2015 Mustang.


Basically says limited slip diff for all models without going into further detail.

Well this is good news. I will be honest this was one area I had not followed nearly as much as I should have.

Good info mostly, except that a larger braking surface does allow for shorter stopping distances. Just because a 12.4 in braking surface can engage ABS doesn't mean it equals the same braking ability or stopping distance in a 15 in rotor. A 12.4 in rotor needs more hydraulic force to engage ABS. A 15 inch rotor requires less, which inherently also requires less time to build the pressure you need to engage ABS. Granted this amount of time isn't a lot but it can save you a couple feet, maybe more. I would have to do a comparison test to be sure.

With that said I believe the Mustang has a booster which senses how fast your pressing the brake pedal so it automatically increases pressure faster, minimizing this benefit even more. Can't remember the systems name.

A few feet? Not really. Maybe 6", MAYBE a foot. Well within margin of error from test to test and surface to surface. I also think you'd be surprised at how much force the brake system takes to actuate. Even with a booster, the difference in master cylinders was pretty minimal from 05-14. There for a while it was thought you'd need the GT500 MC to run the Brembo's but that is definitely false as the stock MC can push enough fluid to actuate the Brembo's at the same levels at the same pedal effort. The biggest downfall was the proportioning valve in the stock MC with Brembo's made for an extremely front biased braking system... more so than normal.

ABS is ABS. If the only thing changed between cars was the rotor diameter you'd see the same braking distances between the two. The larger rotor would be able to maintain that stopping distance for more stops in rapid succession but it would be essentially the same. Certainly within margin of error. The issue comes from trying to test cars with different ABS systems designed around their brakes and factory tires. The different length of time between pulses and the different amount of force as well as the wheel speed indicator before ABS engages are different which can have much larger impacts on stopping distance. It's physics backed by observation.

 

[DivineStrike]

Well this is good news. I will be honest this was one area I had not followed nearly as much as I should have.



A few feet? Not really. Maybe 6", MAYBE a foot. Well within margin of error from test to test and surface to surface. I also think you'd be surprised at how much force the brake system takes to actuate. Even with a booster, the difference in master cylinders was pretty minimal from 05-14. There for a while it was thought you'd need the GT500 MC to run the Brembo's but that is definitely false as the stock MC can push enough fluid to actuate the Brembo's at the same levels at the same pedal effort. The biggest downfall was the proportioning valve in the stock MC with Brembo's made for an extremely front biased braking system... more so than normal.

ABS is ABS. If the only thing changed between cars was the rotor diameter you'd see the same braking distances between the two. The larger rotor would be able to maintain that stopping distance for more stops in rapid succession but it would be essentially the same. Certainly within margin of error. The issue comes from trying to test cars with different ABS systems designed around their brakes and factory tires. The different length of time between pulses and the different amount of force as well as the wheel speed indicator before ABS engages are different which can have much larger impacts on stopping distance. It's physics backed by observation.

Actually I understand just fine that the brake system creates a lot of pressure. But due to the advantages of friction of the larger rotor it requires less pressure to be built up to engage the brakes (i.e. the clamping force) and equal the braking torque of the smaller rotor and will engage ABS faster. Like I said the time is minimal for sure but it is still an advantage, and larger than you realize. Also that advantage would amplify at higher speeds due to greater distances covered over time.



Also, found an explanation of the system i was talking about earlier. A system which minimizes the benefit of larger rotors in a single stop.

 

[908ssp]

You missed my point entirely, and your point is included in my post. My point is the amount of hydraulic pressure required for that amount of force

And you missed my point. Bigger rotors won't contribute to shorter braking distances if the tires are sliding which they are when ABS is engaged.

 

[DivineStrike]

Yes they will, since they will engage ABS faster. so no I did not miss your point. The faster ABS engages the shorter your stopping distances will be.

 

[Trevon]

Yes they will, since they will engage ABS faster. so no I did not miss your point. The faster ABS engages the shorter your stopping distances will be.

Do you get driving advice from the back of a cereal box!?

You stop much faster just before the point your ABS engages (called threshold braking). ABS is much slower for stopping compared to this; You even stop quicker without ABS (depending on vehicle, this is usually the case), just locking the wheels up, but you lose the ability to steer.

 

[JoeDogInKC]

I have a great idea, let's insult our fellow board members. Oh wait, that wouldn't be a good idea at all...

 

[Trevon]

I think it's more insulting to post blatantly wrong information.

 

[Old 5 Oh]

t

K-Brace: My understanding is this is the brace that goes between the strut towers and the firewall which is how a strut tower brace NEEDS to be designed to actually work.

In the Mustang world, the brace you describe is called the Strut Tower Brace. A K-member brace triangulates the K-member, the cradle which holds the engine and mounts the Lower Control Arms. This brace keeps the LCAs from moving inward during high-load situations, stabilizing the front suspension and the front alignment.

I can only speak to the effect on a Fox. A Strut Tower Brace is a night-and-day difference on that floppy old structure. It's so dramatic it's always one of the first things I do when I get a new Fox. I've done the K-member brace a couple of times, and have skipped it more often. It's subtle, but you can (on the Fox) feel a little difference in front grip and stability. The more solid the structure, the less the body moves in reaction to impacts, and the more the suspension complies. Sure is easier to dial in a suspension if the body is not whipping around like al dente linguine.

I can't imagine the S550 will be even faintly related to the Fox, flexibility-wise, but the K-member brace can't hurt on track days.

All that said, if Ford has come up with a new name for a strut tower brace, I'll stand corrected. But those are the terms the industry has been using for 25 or more years.

 

[SVTFreak]

Old 5 oh, I second your post. I kept my mouth shut in case terminology has changed. But you're right. K brace went across the rear lower control arm support struts of the k member.

 

[Tim Hilliard]

It has both, ST and K-Brace. I think Ford should have gone all retro and called the ST a Monte Carlo bar instead, then the purists could have filled 30 pages of thread on why that's improper.

 

[Tim Hilliard]

Old 5 oh, I second your post. I kept my mouth shut in case terminology has changed. But you're right. K brace went across the rear lower control arm support struts of the k member.

My 1980 Fairmont had one, a flattened tube bolted between the rear control arm mounts. Removed it to fit headers and t-sump oil pan. It closed the "K"

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