Whats the best rear brake upgrade for the PP GT's?

[Andy13186]

Yes, for all the drivers that don’t track their car, those 99%, cross drilled rotors are a non issue
By the same token, those 99% don’t need to “improve” their brakes since they don’t track their car
...form over function....

These cross drilled 2 piece rotors took 24 lbs of rotating mass off my car so , yes they did "Improve" my car in multiple ways, not just in terms of braking but acceleration, and every single aspect of performance in addition to looks.

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[luc]

These cross drilled 2 piece rotors took 24 lbs of rotating mass off my car so , yes they did "Improve" my car in multiple ways, not just in terms of braking but acceleration, and every single aspect of performance in addition to looks.

...I’m impressed, it’s the weight of 5 gallons of gas....
And we all know how much faster
And better handling having 5 gallons of gas less make the car be....
Seriously, there is nothing wrong in wanting to have better looking brakes but don’t try to argue that it is a needed or tangible performance upgrade for the street... especially to people like me that race/track those cars....
Btw, I don’t even drive my Mustang (or my Viper Gts) on the street. It’s way to boring ( and too dangerous to push it fast enough to have fun) compared to a road racing track

 

[Andy13186]

...I’m impressed, it’s the weight of 5 gallons of gas....
And we all know how much faster
And better handling having 5 gallons of gas less make the car be....
Seriously, there is nothing wrong in wanting to have better looking brakes but don’t try to argue that it is a needed or tangible performance upgrade for the street... especially to people like me that race/track those cars....
Btw, I don’t even drive my Mustang (or my Viper Gts) on the street. It’s way too boring ( and too dangerous to push it fast enough to have fun) compared to a road racing track

every pound counts, especially rotating mass, you should know this.

 

[Dave TBG]

I gotta admit that I got a chuckle over all the discussion of "reduced weight" and "improved cooling" with drilled and/or slotted rotors. Sure, a few pounds per corner can make a night and day difference in the feel and performance of a vehicle, but I don't recall the OP specifying 2 piece rotors. The difference in weight between a solid rotor and a similar rotor with slots/homes is a few grams, likely less than a 0.1% difference in weight.
In simple terms, a rotor's job is to accumulate, store and dissipate heat. Weight reduction has it's advantages but there are disadvantages as well. A rotor that is 0.1% lighter can only store 99.9% as much heat as the solid version of the same design. If you can't store as much heat, you need to dissipate heat more quickly to make up for it. My understanding is that holes and slots in a rotor aren't really able to increase airflow but they do increase surface area so they do help dissipate more heat. As long as the holes and slots increase the surface area enough to dissipate 0.1% more heat you may even be ahead of the game.

 

[luc]

every pound counts, especially rotating mass, you should know this.

You meant “unsprung” mass...not “rotating “ mass.... Right?

 

[Andy13186]

You meant “unsprung” mass...not “rotating “ mass.... Right?

https://www.cjponyparts.com/resources/what-is-unsprung-weight

Its both rotating and unsprung. There is a difference between rotating mass and unsprung mass although most rotating mass is unsprung, not all unsprung mass is rotating (calipers). And not all Sprung mass is not rotating (portion of driveshaft, flywheel transmission etc)

UNSPRUNG MASS VS ROTATIONAL MASS
There is a common misunderstanding between unsprung weight or mass and rotational mass or inertia. Without diving too deep into the physics behind both terms, rotational mass applies to the parts that must be accelerated or decelerated when the speed of the vehicle changes. This includes items like the driveshaft, brake rotors, wheels, and tires.

It is true that most rotating mass is indeed unsprung weight, as these parts aren’t supported by the vehicle’s suspension. In most cases, a reduction in unsprung weight generally implies a reduction in rotating mass, which in turn helps acceleration. To put it in perspective, rotating mass (such as a wheel or brake rotor) is roughly three times harder to accelerate than sprung weight (such as the additional weight of a passenger or rear seat).

This means that dropping just 10 pounds per wheel with the addition of a lighter set of racing-oriented wheels would equate to almost 120 pounds of sprung weight lost on the car, generally speaking. In most drag racing instances, a 100 pounds lost equates to a tenth or car length in the quarter-mile -- that truly adds up if you’re racing competitively!

 

[BmacIL]

This means that dropping just 10 pounds per wheel with the addition of a lighter set of racing-oriented wheels would equate to almost 120 pounds of sprung weight lost on the car, generally speaking

As the engineering homework used to say: show your work.

Rule of thumb estimates are rotating mass reduction is closer to 4x static, but it depends on many factors (rotational inertia of part in question, percent of mass change, location on car/polar moment effect)

12x? Uh huh lol

 

[Andy13186]

As the engineering homework used to say: show your work.

Rule of thumb estimates are rotating mass reduction is closer to 4x static, but it depends on many factors (rotational inertia of part in question, percent of mass change, location on car/polar moment effect)

12x? Uh huh lol

That says 10 lbs per wheel and you probably know we have 4 wheels, so thats 40 lbs total and 40x3=120, so that quote is saying 3x not 12x. Although I agree for rotors the difference will be less % than with wheels and tires since most of the weight reduction is done near the center of rotation (rotor hat)

 

[luc]

These cross drilled 2 piece rotors took 24 lbs of rotating mass off my car so , yes they did "Improve" my car in multiple ways, not just in terms of braking but acceleration, and every single aspect of performance in addition to looks.

I had to look which Mustang you drive : an automatic, non PP car....
I enjoy shifting gears and a great handling car that can be pushed hard on a road course and where function trumps look
I couldn’t care less about a tenth in the 1/4
Obviously your choice of car is pretty much the opposite
Which is fine

 

[shogun32]

Not to stir the pot, but if the front springs prevent a large amount of chassis motion forward (and thus weight transfer) and the rear wheels are not locking up, and you're not incinerating the rear pads and rotors, why wouldn't you want to maximize the braking of the entire system by maximizing the rear brakes? Granted if you have no driver aids (or the ABS/chassis stability control too slow) and you're prone to locking up the rear which can trivially lead to loss of control, then sure under-utilizing the rears is the far preferable outcome.

The GT350/500 brakes are supersized for heat capacity I'm certain, not to induce the largest possible torque moment into the wheel hub.

I'm good with the entire car 'squatting' flat'ish under maximal braking *provided* the rears don't lock up.

 

[Andy13186]

I had to look which Mustang you drive : an automatic, non PP car....
I enjoy shifting gears and a great handling car that can be pushed hard on a road course and where function trumps look
I couldn’t care less about a tenth in the 1/4
Obviously your choice of car is pretty much the opposite
Which is fine

This post has nothing to do with brakes at all, but lighter weight brakes will help in every aspect of performance and on every track, every dragstrip, every day and all the time, these points are valid and have nothing to do with looks. My car is a performance pack car... and I absolutely guarantee the 10r80 is faster on every type of track and including the dragstrip for many reasons. Ive had 2 manual mustangs and a manual 09 cts-v and I greatly prefer the 10r80 over even the tr6060, the mt82 isnt even close to a decent transmission and in the 18+s the gearing is atrocious. 10r80 will shift faster than anyone on the track, stay closer to the peak power at all times, and have perfect downshifting without even having to think about it while braking. I drive it in paddle mode though because I like the control.

And yes I do have multiple sets of wheels so I can drive hard in corners if I want , my profile pic has my drag setup on. My total rotational mass reduction with these wheels tires and rotors is nearly 100 lbs of rotational mass.

 

[BmacIL]

Not to stir the pot, but if the front springs prevent a large amount of chassis motion forward (and thus weight transfer) and the rear wheels are not locking up, and you're not incinerating the rear pads and rotors, why wouldn't you want to maximize the braking of the entire system by maximizing the rear brakes? Granted if you have no driver aids (or the ABS/chassis stability control too slow) and you're prone to locking up the rear which can trivially lead to loss of control, then sure under-utilizing the rears is the far preferable outcome.

The GT350/500 brakes are supersized for heat capacity I'm certain, not to induce the largest possible torque moment into the wheel hub.

I'm good with the entire car 'squatting' flat'ish under maximal braking *provided* the rears don't lock up.

The weight transfer to the front doesn't change with stiffer springs, only the amount of dive from the weight transfer. Weight transfer is a function of weight distribution, CG, wheelbase and track widths, as well as roll and pitch centers for the F / R suspensions. You're still putting way, way more load on the front than the rear under hard braking. The GT PP brake setup has a lower friction rear compound due to the limitations of how much rear brake torque you can apply before ABS engagement limits overall brake performance. Also safety margin for a street car. There have been several examples of people running the same high-friction track compound F / R that experience instability or less overall performance. This is why G-LOC/Carbotech and others recommend a one step compound stagger. Going to too large a compound stagger will also reduce ABS performance, for the reason you're alluding to: under-utilizing the rear. This can happen if you use something like an R10 or R12 front with a regular street-only rear pad.

As tire grip F / R and in particular aero loads go up, the rear can tolerate more torque before lockup, thus increasing the need for higher friction pads or larger rotors. Track cars with big wings will need more. Street cars with little to no added downforce really don't.

 

[luc]

This post has nothing to do with brakes at all, but lighter weight brakes will help in every aspect of performance and on every track, every dragstrip, every day and all the time, these points are valid and have NOTHING to do with looks. My car is a performance pack car... and I absolutely guarantee the 10r80 is faster on every type of track and including the dragstrip for many reasons. Ive had 2 manual mustangs and a manual 09 cts-v and I greatly prefer the 10r80 over even the tr6060, the mt82 isnt even close to a decent transmission and in the 18+s the gearing is atrocious. 10r80 will shift faster than anyone on the track, stay closer to the peak power at all times, and have perfect downshifting without even having to think about it while braking. I drive it in paddle mode though because I like the control.

And yes I do have multiple sets of wheels so I can drive hard in corners if I want , my profile pic has my drag setup on. My total rotational mass reduction with these wheels tires and rotors is nearly 100 lbs of rotational mass.

You missed the point completely
What, for me, make a manual so much more enjoyable are both the total control and the fact that it require skills to use it
There is pleasure in a job well done and on a road racing track, changing gears is usually where mistake can happen. And multi tasking correctly such as braking, shifting and turning at the same time is very rewarding

 

[fatbillybob]

This post below from Zeckhausen racing in tight with Stoptech brakes helps to explain the issue of brake balance that seems to be missing in this thread. This is a critical key whenever you depart from OEM brake systems and even when you start playing with pad compounds and pad stagger and as racers and with highly modified chassis because we change the chassis dynamics outside OEM intent. This is part of our testing and development of our racer cars even if using cockpit adjustable bias because you want to know what each click of bias change is going to do well before you get to the braking zone.



<<The brake torque at any one wheel is the product of three terms:

• Rotor Effective Radius (approximately the distance from the center of the hub to the center of the brake pad)
• Clamping Force (Hydraulic pressure times effective caliper piston area)
• Coefficient of friction between the brake pad and the rotor

If you increase the diameter of the rotor, the brake torque goes up. But you can compensate by using a lower Cf pad or by decreasing the size of the caliper pistons (or both). Thus, it is possible to have larger front brakes which produce the same brake torque as the original factory brakes. All you've done is increase the thermal capacity of the system without changing the balance.

It's the same in the OEM world, except that the OEM brake designer can also play around with master cylinder bore sizing. So they have even more design flexibility than the BBK manufacturers. Bigger front brakes do not always imply more front brake torque (or what many call "stopping power").
Is the brake bias going to rear? Is this legal?
The brake bias is shifted rearword (in the specific case of the 350Z example) but is still front biased. It's just less front biased than it was originally. But you can't just do this blindly, because you may end up with an unstable system. That's why StopTech uses the Modified J-Turn test to ensure that stability control is not adversely affected and that's why they do the ABS-off test to make sure the car is stable even if ABS fails. Somtimes there are conflicting requirements. Additional rear bias may improves 60-0 mph stopping distances, but the ABS and J-Turn tests reveal a problem. So the bias is shifted slightly forward by going up to the next larger piston size and the test is run again.>>

 

[sigintel]

Whats the best rear brake upgrade for the PP GT's?

1 x 80# sand bag in trunk

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