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The Big Bad Brake Thread



Thats not how science works.

You're supposed to defend your own theory.

Not force others to prove you wrong.

Regardless...

Heres a small example...

Car guy upgrades his GP to 12" front brakes, stock calipers, and sport pads.

3500 lbs total

65%/35% F/R

F: 2275 lbs
R: 1225 lbs

theoretical weight transfer based on stoptech example using our mass.

0.7 G deaccel

36% weight increase in front.

F 3094 lbs
R 406 lbs

Tire coefficient is 0.8 mu for street tire thus

Traction available:

F 2475.2 lbs max braking force avail
R 324.8 lbs max braking force avail

324.8/2800 = 11.6%

Thus rear brakes do 11.6% of the work.

Car guy finally decides its time for some better rubber.

lets say 0.8 G deaccel and 0.9 mew.

40% increase in front

F 3185 lbs
R 315 lbs

0.9 mew

traction available

F 2866.5 lbs
R 283.5 lbs

283.5/3150= 9%

Thus rear brakes do 9% of the work with better tires.

Note none of these numbers are worth anything due to the following:

I assumed no passenger mass.

Just vehicle mass (~3500 lbs for a 3.8L equipped 97-08 grand prix)

Weight transfer based on this graph: http://stoptech.com/tech_info/img/brakebias_3.jpg

from here: StopTech : Balanced Brake Upgrades

Which clearly does not represent the weight transfer we experience since no one has sat down and calculated our centre of gravity, suspension spring rate and strut dampening rates.

Also max decell rates were assumed as were tire coefficient of friction.

The summary is that you cannot speculate that because one thread of logic dictates you are correct, that this applies to all vehicles.

This is why something as simple as tire choice and even inflation levels can change how a vehicle responds to a modification.

Now go do some math that proves your point.
 
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So just because my logic applies to most vehicles, you're saying it may or may not apply to ours? I guess you have a point. I agree that exact math on these cars would be way too much work just to calculate stopping distance. It would be much easier to do an actual experiment by finding the 60-0 stopping distance on stock brakes and then switching to 12" brakes with the monte brackets using the same old caliper and pads. This will still be slightly off since there will be a new rotor. I still believe that if the fronts lock up first, moving some of the bias to the rear will decrease braking distance.
 
HERES MORE!

Onto brake calipers...


Stock front calipers:

63.5 mm bore.

for 1 mm stroke,

3168.20 cubic mm

04+ GP calipers are the same.


06+ imp

45 mm bore x2

1 mm stroke x2

1591.07 cubic mm x 2

total 3 182.14 cubic mm

Thus nearly the same.

Simply a larger pad, more pots for more even force distribution.


Now lets look at F body calipers:

Also a 45 mm bore... Same numbers as the 06 imp calipers.


Now lets look at C5 calipers, non Z51 or Z06.

Edit: turns out Z51 brake package used the same calipers, different brackets, and a 13.19" rotor versus a 12.8" rotor. At least in the front.

40.5 mm bore x2

for 1 mm stroke x 2

1288.77 cubic mm x2

Total 2 577.53 cubic mm

3168.20 - 2577.53 = 590.67

590.67/3168.20 = 18.6% smaller.


More fun:

Master cylinder bore is 1" so 25.4 mm.

You apply 1" of pedal, 25.4 mm.

thats 12 875.55 cubic mm of displacement.

stock calipers are 63.5 mm bore.

V=pi*R^2*h

thus both front calipers must move a combined 3.84 mm.

Thus one caliper moves 1.92 mm for 1" of applied pressure.


Now onto rotors....

http://stoptech.com/tech_info/formulas _vehicle_braking_dynamics.pdf

Tw = Ps x Ap x μ x 2 x Re

lets assume 1200 Psi (8273708.75 pascals) is being applied to the caliper.

A= 2Pi*r

Ap = 2*Pi*31.75

Ap = 199.49 mm^2 (0.00019949 m^2)

Lets assume a decent mu of 0.5

Our '12 inch' rotors are 303 mm (0.303 m)

Our '11 inch' rotors are 278 mm (0.278 m)

04+ are 297 mm (0.297 m)


Stock:

Tw = 8273708.75 Pa*0.00019949 m^2*0.5*2*0.278 m

Tw = 458.85 joules


Stock calipers w/12" rotors:

Tw = 8273708.75 Pa*0.00019949 m^2*0.5*2*0.303 m

Tw = 500.11 joules 9% increase

Tw = 500.11 N*m = 368.86 ft lbs


04+

Tw = 8273708.75 Pa*0.00019949 m^2*0.5*2*0.297 m

Tw = 492.01 joules

Tw = 492.01 N*m


F body calipers w/12" rotors:

Ap = 282.74 mm^2 (0.00028274 m^2)

Tw = 8273708.75 Pa*0.00028274 m^2*0.5*2*0.303 m

Tw = 708.81 joules 55% increase

Tw = 708.81 N*m = 522.79 ft lbs


C5/C6 calipers w/12" rotors:

Ap = 254.47 mm^2 (0.00025447 m^2)

Tw = 8273708.75 Pa*0.00025447 m^2*0.5*0.303 m

Tw = 637.94 joules 39% increase

Tw = 637.94 N*m = 470.52 ft lbs.


GXP Fronts

Tw = 8273708.75 Pa*0.00028274 m^2*0.5*2*0.323 m

Tw = 755.60 joules


Earlier guess of an increase in front brake "capacity" of ~29% with sportier tires suggests we should have 29% more front brake power.

Seems in this comparison the F bodies are a terrible choice and the C5's are better, but not ideal.

Again, all going on some assumptions which we do not know the answers to.

All bore information based on sheets like the following from centric via rock auto: http://www.rockauto.com/catalog/moreinfo.php?pk=2052622

Also the incorrect Re's were used because its kinda difficult to calculate the radius of clamping when its not just one point.
 
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Now take this one with a grain of salt...

Simply because he claims the following:

Brake Pads: Think of stopping a spinng wheel with two (2) fingers vs five (5) fingers. More area equals greater friction. It is also important to know that the greater the mass (volume) the more material there is to absorb heat, as heat will glaze the pads and cause brake failure. All of this should be taken into consideration when purchasing calipers.
Click to expand...

Friction isn't based on surface area.

Its not the pad's job to absorb heat. In fact, if it absorbs too much, this energy will be transfered to the caliper and then the brake fluid.

Thus causing your brake fluid to boil over.

Then you're in real trouble.

If the pads are overheating then you have one of the following issues:

Insufficient air flow to rotors to cool them down.

Insufficient rotor size (insufficient heat capacity)

Incorrect pad material for the heat range experienced.

Now here is the link: Brake Article© by Dean Oshiro

Note: I chopped out things I found irrelevant to our application. Click the link for the full article.

Power Boosters: Power boosters were needed when disc brake systems were being used more and more on factory cars. The amount of boost created from the booster is directly related to the square inches of the booster and the inches of vacuum imputed from the engine. Since the disc brake calipers required a greater volume of fluid due to the size of the pistons and the clamping force (some times up to 6 tons), the master cylinder requires a bigger diameter bores to push the required volume of brake fluid. When you increase the bore size you reduce the output pressure of the master cylinder. In order to boost the pressure output of this larger bore master cylinder the factories installed a power booster. Power booster range in size from 7" to 11".

This is the formula to figure your output booster pressure.

Force in pounds = (Diaphragm area in square inches) x (manifold vacuum in inches Hg) x ½

Example: 7” single diaphragm booster with 17 inches of vacuum. 3.5” x 3.5” x 3.14 = 38.465 square inches x 17 inches of vacuum x 50% = 326.95 psi

Here is quick table for your reference;Maximum Diaphragm Force in Pounds

Inches Hg 7 inch 9 inch 10 inch
15 289 477 589
16 308 509 628
17 327 541 668
18 346 573 707
19 366 604 746
20 385 636 785



Of course this it based on the booster being 100% efficient, a good rule of thumb would be 80 to 85 percent efficient.

Booster Master Cylinder Combinations: When ever possible you should always replace the existing booster with another one of similar size and design. Engineers designed the booster/master cylinder based on the weight, tire size, calipers, rotors, etc. However when you change anything on your vehicle it effects other parts that was engineered to be compatible with the part you changed.

When choosing a booster/master cylinder take all the factors into consideration.

4. You will need to calculate the combined pressure of the booster and master cylinder so the combined pressure is about 1,000 psi. Of course we would want to put the smallest bore master cylinder with the booster we have chosen. If if you choose too small of a bore, you will run out of brake fluid or you might have too much out put pressure causing your pedal to feel spongy or to sensitive.
Click to expand...

With this in mind....

Now consider why the 2000-2005 Impala came with a smaller brake booster and larger rotors relative to the 1997-2003 Grand Prix.

This explains how they use the same master cylinder.

On second thought, this would just reduce overall pressure. Unless they changed the proportioning valves as well....
 
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See I was going to go into all of that but then I realized what he's trying to do...

He's trying to get the rears to lock up so he can drift his FWD car :D

In all seriousness though, I have locked up the CTS-V calipers and I did a J Clark impression with my face, I could feel the rear become very light, but nothing that was uncontrollable. Again I understand where you were going with the rear brakes need the balance, but on a street car like these with such attributes of a Sumo Wrestler, we aren't track racing these cars in autox or road course. Its not really worth it for street application, just upgrading the front is more than enough. We will understeer regardless of how good our rear brakes are just because of the fact that we have a big Iron Block hanging out over the front axles/suspension
 
550 lbs of win?

Also turns out i forgot a 2 in the Tw formula..... hooray latenightmath.

In other news.

06+ impala rear rotors should be 3.9 lbs lighter than 97-08 rotors.


97-03 GP: http://www.rockauto.com/catalog/moreinfo.php?pk=1279970

Here it is again converted to metric. Rounding errors most likely account for the inaccuracies: http://i88.photobucket.com/albums/k180/matt5112/converted97Rrotors.jpg

Edit.... found a more accurate one direct from centric: http://extranet.soleniuminc.com/CentricParts/Inquiry/viewDetails.aspx?p=120.62058&a=263443&ic=1&i=1&

11.2 lbs

not 15 lbs


06+ Imp: http://www.rockauto.com/catalog/moreinfo.php?pk=1279135

11.1 lbs


04+ GP: http://www.rockauto.com/catalog/moreinfo.php?pk=1279678

Don't appear to be compatible with 97-03's though.... height is wrong.

10.5 lbs
 
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I dont see why you are bringing all these numbers into play when they have nothing to do with what im talking about (other than the weight distribution...kind of), with all respect. I also wasnt arguing any facts about uprading tires. Imagine a bike capable of doing a stoppie (ignore the fact that the front and rear are controlled separately) the front tire is capable of holding all the friction in a 100% front weight distribution. The brakes are obviously enough to handle all of the stopping force, there is probably a little extra, but the rider doesnt want to go face first into the cement. So do you really think you need more braking power in the front? Even in your example, if the rear tires only contribute 9% of the stopping force, that doesnt mean that the rear tires are exerting the maximum stopping friction. What would happen though is that if you increased the stopping friction on the rears, there would be more weight transfer to the front, thus less available tracton to the rears. A little ironic, yes.

I totally agree that larger front brakes with greater stopping force will help in most areas of braking, except stopping distance. The effect of moving the brake bias toward the rear is probably miniscule at best, but moving the bias towards the front is not going increase the amount of stopping friction that the front tires can exert.
 
JoRoW99 said:
I dont see why you are bringing all these numbers into play when they have nothing to do with what im talking about (other than the weight distribution...kind of), with all respect.
Click to expand...

Did you read what I typed and understand it?

JoRoW99 said:
I also wasnt arguing any facts about uprading tires. Imagine a bike capable of doing a stoppie (ignore the fact that the front and rear are controlled separately) the front tire is capable of holding all the friction in a 100% front weight distribution. The brakes are obviously enough to handle all of the stopping force, there is probably a little extra, but the rider doesnt want to go face first into the cement. So do you really think you need more braking power in the front? Even in your example, if the rear tires only contribute 9% of the stopping force, that doesnt mean that the rear tires are exerting the maximum stopping friction. What would happen though is that if you increased the stopping friction on the rears, there would be more weight transfer to the front, thus less available tracton to the rears. A little ironic, yes.
Click to expand...

Its all about balance.

As you increase your deceleration, you increase weight transfer.

Which reduces the amount of braking the rear wheels can do.

JoRoW99 said:
I totally agree that larger front brakes with greater stopping force will help in most areas of braking, except stopping distance.
Click to expand...

If you had read, you would know that larger brakes are for heat capacity.

Not stopping force. You can easily increase stopping force with a different brake pedal, brake booster, master cylinder, caliper bore, or pad composition.

JoRoW99 said:
The effect of moving the brake bias toward the rear is probably miniscule at best, but moving the bias towards the front is not going increase the amount of stopping friction that the front tires can exert.
Click to expand...

Increasing grip increases the stopping force the front tires can handle before locking up.

This is because you experience more weight transfer due to the higher deceleration rates.

Is it enough to justify F bodies or 06+ imp setup? No. You'll just lock up your fronts all day long.

But the 12" upgrade might just be a good idea for those with stickier tires who drive aggressively and notice excessive cracking in their rotors.
 


Rear brakes:

GXP rear:

Ap = 131.95 mm^2 (0.00013195 m^2)

Tw = 8273708.75 Pa*0.00013195 m^2*0.5*2*0.305 m

Tw = 332.97 joules


Stock rear:

150.80 mm^2

Tw = 8273708.75 Pa*0.00015080 m^2*0.5*2*0.278 m

Tw = 346.85 joules

And no, rears would never see this kind of pressure (1200 PSI) but still.

Just kinda shows compared to each other, the GXP rear setup actually has less clamping force.

I've also added GXP's to the list up above, and it seems they're the best front brake solution ever equipped to our vehicles from factory.

And the rear GXP setup is for looks as well as keeping the rotors cooler considering they're vented versus the solid non GXP rotors.
 
matt5112 said:
Its all about balance.

As you increase your deceleration, you increase weight transfer.

Which reduces the amount of braking the rear wheels can do.
Click to expand...

Yes, that is basically what I said.

matt5112 said:
If you had read, you would know that larger brakes are for heat capacity.

Not stopping force. You can easily increase stopping force with a different brake pedal, brake booster, master cylinder, caliper bore, or pad composition.
Click to expand...

That is why I specified that bigger brakes with a larger clamping force would help in most areas. (I apologize as I should have said clamping force in my original post now that I reread it) except braking distance (which is the only factor I am trying to discuss) I know that brakes with more mass or cooling efficiency will reduce brake fade. after all, braking is essentially turning mechanical energy into heat.


matt5112 said:
Is it enough to justify F bodies or 06+ imp setup? No. You'll just lock up your fronts all day long.
Click to expand...

Thank you, that is the exact point I have been trying to explain all along.
 
In a round about way... I'm trying to say, do some math that supports your argument. :)

What I've left you with is....

The GXP setup....

Most force available in the front.

Least in the rear.

Yet the cars are considered as having the best factory brakes from 97 and up.

After all of that.... I think I want rear GXP's and front stock calipers and 12's or possibly C5's.....
 
If I ever do a 12" front brake upgrade (just because its like $40 extra), or hell maybe just when I change my rear pads and rotors, Ill see if I can nail down some 60-0 distances.
 


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