The point of diminishing return on brakes?

[Nicks67GTO]

Just wondering where everyone thinks the point of diminishing return is for a typical GM A body street car brake system is is. Call it 3900 lbs that will never really see much over 100mph in most instances and 135mph tops. 90% street 10% autox /drag. Maybe a road course here and there.

At some point you have to be paying for more bling and less and less advantage. For instance a nice set of Kore3 C6 Z51's are very nice and will obviously get it done quickly for around $1,100....Then there are the ZR1 carbon ceramics that run $10K+. While they are totally out of my price range and never going to happen regardless, i'm sure they are better but they would probably be little advantage over a nice C6 setup in almost every situation I would encounter. Where are the big gains made on brakes? Is it rotor diameter/ mechanical lever arm? Caliper piston numbers? Caliper piston diameter total area?

When are we just buying brakes for the sake of buying expensive brakes?

[wayward]

I am in the same boat but I probably won't ever be allowed to run a road course because I have a vert. Although I want to have a fun car with the best bang for the buck. There are several major areas for thought, that I was made aware of.

braking force specs- experts please discuss
Rotational weight - experts please discuss
Heat dissipation
Do you have wheels, will they fit/ brake reveal
Cost

For my purpose heat shouldn't ever be a concern, rotational weight- I went with a one piece due to cost, I bought my brakes first and told the wheel guys what they were to ensure the calipers would fit.

I did Wildwood - 13" 6 piston frt/ 12" 4 piston rear & polished master... It was about $2k, I looked into the z-51 & Z06 brakes but after I did the dollar math of all the parts for the corvette brakes. I decided to go new combo setup. I could have gone larger rotors but I chose 17" wheels for the sidewall looks.

[vette427-sbc]

Take a look at the new stickie thread by Ron and Tobin... Lots of good info about this subject

[Ron.in.SoCal]

Take a look at the new stickie thread by Ron and Tobin... Lots of good info about this subject

Yep:

https://www.pro-touring.com/threads/104584-Brake-sizing-and-selection-tutorial-featuring-Ron-Sutton-and-Tobin-of-KORE3

[1989GTA]

Not sure how much of this was addressed in that thread especially using a power brake booster. There are a lot of cars out there running the 69-72 GM disc brake set up. I can think of two calipers that can be used but how much better are they than the single piston 2 15/16" factory one. I don't know about rotors such as a lighter weight two piece maybe of larger diameter? The brackets available to install a larger diameter rotor? I have a lot of questions myself.

[andrewb70]

I think that once you step up to a well sorted out C6 Z51 brake package, you will have reached a point where any more and the gains are not worth the effort. I say this with a typical car that is driven 90% on the street.

Andrew

[1989GTA]

I think that once you step up to a well sorted out C6 Z51 brake package, you will have reached a point where any more and the gains are not worth the effort. I say this with a typical car that is driven 90% on the street.

Andrew

I wonder how that set up would compare to the 69-72 disc brakes if they had say the EBC red stuff or yellow stuff pads or something like the Hawk HP+ pads? Would it be something as simple as upgrading the pads to acheive the desired results?

[bovey]

I wonder how that set up would compare to the 69-72 disc brakes if they had say the EBC red stuff or yellow stuff pads or something like the Hawk HP+ pads? Would it be something as simple as upgrading the pads to acheive the desired results?

Depends on the rest of your car.

For example: I put a 12.19 Wilwood kit on the rear of my truck and was going to put 13s on the front. However, I have what they call the big GM fronts (cop car stuff) and with a set of Hawk HP+ pads, it worked amazing.

Read Ron and Tobin's link posted above, it is gold. Also read Ron's thread on safety:
https://www.pro-touring.com/threads/103597-Safety-for-Pro-Touring-Track-Cars

And if you have a c-clip rear-end understand pad knock back. Here is my thread on the subject.
https://www.pro-touring.com/threads/101080-Soft-Pedal-vs-Axle-Runout-solutions-Willwoods-(fixed-callipers)-on-a-12-bolt-GM?highlight=axel+runout

[andrewb70]

I wonder how that set up would compare to the 69-72 disc brakes if they had say the EBC red stuff or yellow stuff pads or something like the Hawk HP+ pads? Would it be something as simple as upgrading the pads to acheive the desired results?

I had stock GM disk brakes on my 70 GTO and they sucked. For a long time, the hot set-up was using the b-body 12" rotors and calipers. I think going with the more modern brakes gives you better modulation, heat dissipation, and is probably lighter.

Andrew

[1989GTA]

I have been looking at 3 Wilwood kits and they all come with a .81" wide rotor. Any thoughts on a .81" wide rotor for primarily a high performance street application. I am also interested losing weigth in both rotating and sprung.

[Bad94]

C5 brakes are a very good with the right rotor and pad combo.

[Randy67]

I have been looking at 3 Wilwood kits and they all come with a .81" wide rotor. Any thoughts on a .81" wide rotor for primarily a high performance street application. I am also interested losing weigth in both rotating and sprung.

I wouldn't use the .81 rotor on the front of a street car unless it is really light (2500 lbs or less). Just not a lot of mass to absorb heat. They may be okay for the rear though.

[TheJDMan]

I think that once you step up to a well sorted out C6 Z51 brake package, you will have reached a point where any more and the gains are not worth the effort. I say this with a typical car that is driven 90% on the street.

Andrew

I would agree! In addition, the C6 calipers are so well supported that one can tune the brake system by simply using different pad compounds as necessary.

[wayward]

I have been looking at 3 Wilwood kits and they all come with a .81" wide rotor. Any thoughts on a .81" wide rotor for primarily a high performance street application. I am also interested losing weight in both rotating and sprung.

you can step up to a two piece rotor to reduce weight... but in my opinion this is hard to be and can be had for about a $1K for the front setup w/ alum hubs
1967 Pontiac GTO - Front Brake Kit No.: 140-12271 (wilwood part number) - this is what i used on my car..

[1989GTA]

you can step up to a two piece rotor to reduce weight... but in my opinion this is hard to be and can be had for about a $1K for the front setup w/ alum hubs
1967 Pontiac GTO - Front Brake Kit No.: 140-12271 (wilwood part number) - this is what i used on my car..

I was looking at that kit but the .38" offset scarred me off. I am running 245/45ZR17 tires on the front and they barely clear the outer fender lip as it is. In fact they will rub under certain situations.

I am running the 69-72 disc kit swap for the fronts now. I can't afford to go any wider. If I knew for sure they would not be any wider I would give them a real hard look.

[Aficionado]

In figuring the advantage of different brakes, don't forget the advantage of reduced unsprung weight when you go to a lighter caliper. I went from the stock cast iron 4-piston calipers on my '72 Corvette to the Wilwood 6-piston front/4-piston rear setup and dropped about 5 pounds per wheel.

Might be another thing worth comparing between the brakes you're considering.

[a67]

I wouldn't use the .81 rotor on the front of a street car unless it is really light (2500 lbs or less). Just not a lot of mass to absorb heat. They may be okay for the rear though.

Both myself and GM disagrees. Need to also take into account the diameter of the rotor. Which is better: a 10.5" diameter by 1" thick, or a 12" diameter by .81" thick rotor? Single piston iron caliper, or a 2 piston aluminum caliper?

Bob.

[1989GTA]

Both myself and GM disagrees. Need to also take into account the diameter of the rotor. Which is better: a 10.5" diameter by 1" thick, or a 12" diameter by .81" thick rotor? Single piston iron caliper, or a 2 piston aluminum caliper?

Bob.

Thats just it. I like the Wilwood 140-10510 kit with the 12.19 x .81" rotor that has 6 pistons with an area of 5.06 in/sq. Then the question is how much better is that than the 11 x 1" rotor and a single piston with 6.78 sq/in with EBC "redstuff" pads. This is what I am mulling over in my mind.

The above kit 140-12771 has a iron 12.90" x 1.10" rotor and a 4 piston caliper with an area of 4.04 sq/in. That kit appears to be Wilwoods version of the Corvette C5 brake. Also there does not appear to be much of a weight reduction with that kit.

[a67]

The brakes pads used will make or break a good braking system. Brake systems are just that, a system. Need to take into account every part involved. Up the Tobin/Ron sticky I posted a spread sheet that will calculate the resulting braking force (see page 7 of thread). Run some numbers through it for the various front brakes you are considering.

Can also change the pad friction to see that affect.

As far as rotor size, this is dependent upon the use of the brakes. If a lot of braking is expected, then more rotor mass helps. Better pads also help. The downside to more rotor mass is more unsprung weight, more rotational weight, and the need for larger wheels.

Bob.

P.S. link to brake calculator spread sheet:

https://www.pro-touring.com/threads/104584-Brake-sizing-and-selection-tutorial-featuring-Ron-Sutton-and-Tobin-of-KORE3?p=1050721#post1050721

[1989GTA]

Hi Bob

I did the run my current setup through the calculator and came up with a tire force of 3024 lbs. This is using the EBC red stuff pads with a cf of .45 that I will be adding. However I am running a dual 8" power brake booster. So how much do you add for that? I will go ahead and run the other brake kits through it and see what happens. Thank You for posting the calculator.

[1989GTA]

Ok, I ran a number of Wilwood front disc brake kits through the calculator. Leaving the rears on my car alone with the EBC red stuff pads. The rears have the metric caliper with a 2.12" diameter.

The closest kit to mine was Wilwood 140-7675 with a total tire force of 2580. From there they went down to a low of 2328 total tire force. It appears that the big single piston caliper of 2.9375" that is one on my car now and it really drives the total tire force up with 3024. That is with the EBC red stuff pads with a CF of .45. It appears that from that stand point I should just refine what I have.

[1989GTA]

Playing with the calculator and changing the pad coefficient from .45 to .35 made a big difference with my brakes. With a .45cf the tire braking force is 3026. When I change the cf to .35 it drops to 2356. That is huge. By the way my brake bias is 66% front and 34% rear. Heck, for all I know the original pad CF could have been .30. I don't know what pads come in these cheaper conversion kits.

[a67]

Hi Bob

I did the run my current setup through the calculator and came up with a tire force of 3024 lbs. This is using the EBC red stuff pads with a cf of .45 that I will be adding. However I am running a dual 8" power brake booster. So how much do you add for that? I will go ahead and run the other brake kits through it and see what happens. Thank You for posting the calculator.

Can estimate the added boost from the booster. Take your 8" dual for example. The diameter of the actual diaphragm is likely less then 8", say it is 1" less is diameter due to the mounting of the diaphragm. For a radius of 3.5", the area is: a = pi * r^2

For 38.4 sq In, then times 2 for dual: 77 sq inch total area. Now it gets tricky, at sea level the air pressure is about 14.7 psi. Say there is 16" of vacuum from the engine, that is about 8 psi. Subtract that from the air pressure for: 6.7 psi

Against the area of the booster: 77 * 6.7 = 516 pounds of force added by the booster. Which is close to the 'general' 600 pounds of added force by a 'normal' size booster. A dual 9" booster would add 673 pounds of force (using same calc as above with the larger diaphragm).

Then a single 11" booster would add 526 pounds of force. All of this also shows why 7" boosters are not a good idea (379 # of force for a dual).

One big note here, I'm still on my first cup of coffee. Feel free to correct or add to this.

Bob.

[a67]

Playing with the calculator and changing the pad coefficient from .45 to .35 made a big difference with my brakes. With a .45cf the tire braking force is 3026. When I change the cf to .35 it drops to 2356. That is huge. By the way my brake bias is 66% front and 34% rear. Heck, for all I know the original pad CF could have been .30. I don't know what pads come in these cheaper conversion kits.

Yes, the pads used is very important. Most pads have the rating printed on the edge of the pad material. Such as EE, EF, FE and so on. The higher the letter the higher the friction. The first letter is cold rating, the second letter is the hot rating. The range for each letter is also quite a bit:

Code: Coefficient of Friction:

C Not over 0.15
D Over 0.15 but not over 0.25
E Over 0.25 but not over 0.35
F Over 0.35 but not over 0.45
G Over 0.45 but not over 0.55
H Over 0.55
Z Unclassified

An real-life example for me was going from a PBR FE rated pad to Stoptech Performance street pads rated at FF. Even cold the Stoptech pads are much higher in friction.

Bob.

[1989GTA]

Thanks Bob. The car is in the shop getting a number of punch list items done including the brakes. I will try and get the original pads and see what the rating was/is on them. I am also having the proportioning valve changed out as it might very well have been a disc/drum unit. This way I will know for sure it is a disc/disc unit. So with that and the new pads the brakes should be greatly improved. I will know later this week. Love that calculator.

Edit: With everything done my brake tire force should be around 3500-3600. I estimate my car empty will be around 3500-3600 lbs. So with a couple of passengers that would put it close to 4000 lbs. That should be enough force to get it done.