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Old 12-01-2005, 11:11 AM
Doc Doc is offline
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Default The Final Word on front disc brakes

As you can see from the other threads I've been doing a lot of thinking and research regarding front brake options. I decided to compile a list of some of the common options to aid in planning.

First off, DISCS. A larger disc is effectively a larger lever arm for the brakes to act against. I made a little table to compare the expected effectiveness of larger rotors. The brake pad rides towards the outside of the disc, but the force is spread over a wide band of contact, not just the outermost edge. In my calculations I assumed that the pad was 1.5" wide. Therefore the center of the pad (or 0.75" in from the edge of the disc) was where the force would be concentrated. This may not be 100% accurate but it should yield a good comparison as long as it is consistently applied.

Keep in mind that this chart is Disc properties ONLY:

Disc OD: Effective Radius: Theoretical improvement:

10" 4.25" 0% (OEM size)
11" 4.75" 12% (Standard B-body brakes; also used in some aftermarket kits)
12" 5.25" 24% (B-Body heavy duty rotor such as IROC or "police brakes"; also aftermarket kits offered by Baer, Wilwood, etc.)
13" 5.75" 35% (Largest aftermarket kit offered by BAER)
14" 6.25" 47% (Listed for custom purposes only)

....as you can see the trend is roughly 12% per inch.


Now for the calipers. The effectiveness of a caliper is based on the area of the piston(s). In the case of 4-piston calipers where there are two pistons on each side of the disc, only the area of one side of the caliper counts.

Caliper: Piston Dia & Count: Effective Area: Improvement:

Stock GN 1x 2.48" 4.8 sq. in. 0%
OEM- Oversize* 1x 2.75" 5.9 sq. in. 20%
Wilwood Dynalite 4x 1.75" 4.8 sq. in. 0%
S-10 Blazer 2x 40mm 3.9 sq. in. -19% (performance LOSS!)
PBR Caliper (Baer)** 2x 38mm 3.5 sq. in. -27% (again, LOSS!)

*"OEM-Oversize" is the OEM style aftermarket calipers such as those made by Wilwood and US Brakes. They are the same style as the stock GM calipers but they have a larger piston. These calipers would be a direct swap for factory GN calipers. This is also the same piston size as the "big brake" option for the B body GM cars. If you use the "Police Package" brakes from a Caprice those also have a single 2.75" piston. However, the B Body calipers are a different style than the GN caliper; to use the B body calipers you have to use B body spindles.


**The often lauded Camaro/Corvette calipers are also 2x 38mm like the PBR, etc.


The Caliper info is interesting because it seems that the only real upgrade to be had here is the OEM style oversize calipers. That's interesting becasue they are among the most inexpensive as well.

These numbers are multiplied together when considering a full conversion. So, some examples might be:

B body swap with IROC rotors and Police Package Calipers 1.24 x 1.20 = 49% improvement

Wilwood aftermarket kit (12" rotors and Dynalite caliper)= 1.24 x 1.00 = 24% improvement

10" Discs + Overize OEM style caliper such as the US Brake = 1.00 x 1.20 = 20% improvement

12" Discs + Blazer calipers = 1.24 x 0.81 = Almost no improvement

13" Discs + PBR calipers (Baer kit) = 1.35 x 0.73 = 2% LOSS! (Perhaps this is why Baer recommends swapping in a smaller bore master cylinder???)

Of course, this information is only part of the puzzle. Larger discs are also good for better cooling. So, even though the above example of the Baer kit would respond in a small LOSS in braking power, the 13" discs in that kit WOULD have much better fading resistance compared to stock. For autocross or road course driving they would be far superior to stock due to this.

Likewise, some calipers are stiffer than others. My comparison was of clamping pressure only. Perhaps some of the calipers are stiffer than others, which might offer a benefit that I did not take into account.

Last edited by Doc; 12-02-2005 at 09:56 PM.
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Old 12-01-2005, 01:29 PM
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Default Re: The Final Word on front disc brakes

Great stuff! Sticky!
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Old 12-01-2005, 04:05 PM
Turbobuick Turbobuick is offline
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Default Re: The Final Word on front disc brakes

Doc,
I think you are looking at the caliper sizes a little wrong. The size of the piston does not necessarily determine the performance of a caliper. The absolute biggest determining factor is going to brake surface area, IE the size of the pad. How the caliper distrubtes clamping force on the back of the caliper, single v.s. dual v.s. four piston calipers. A dual piston PBR caliper has a MUCH larger brake pad surface area and the caliper distributes the clamping force MUCH more evenly over the rear of the pad than a stock caliper. Same thing is true for the 11" S10 balzer upgrade. That brake upgrade is going to be significantly better than the stock brakes because it has a significantly larger brake surface with calipers that distribute pressure more evenly. It's not how hard the caliper clamps but how much surface area and how it is distributed that make the difference.

There are other factors that play into this also including how the caliper is mounted. The PBR is a full floating design and not a fixed mount design like the Dynalite in the Wilwood kit. I don't know enough about this stuff but I do know that is important in a road race/ street car brake setup.

Just my point of view, thanks for compiling the info though and it is good for comparing the differences.
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Old 12-01-2005, 05:24 PM
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Default Re: The Final Word on front disc brakes

That is only partially true...

Brakes work based on friction. The frictional force between two sliding objects is based ONLY on TWO factors:

1. The Normal Force, or in Layman's terms, the force holding the two objects together. (In our case this is the clamping force exerted by the caliper onto the pads and rotor)

2. The coefficient of friction, which is a property of the materials that the sliding objects are made of. (In our case, this has to do with the materials used for the rotor and the brake pads). When you swap to "high grip" brake pads you are changing this property.

You can look up this equation in any basic Physics textbook. Note that the AREA of the contact (for example, the size of the pads) does not enter into this equation at all. I know it is counter-intuitive, but it is true.

Now then, larger brake pads are going to be more DURABLE than smaller ones, becasue the energy lost to friction is spread out over a larger area. So yes, in a way larger brake pads and larger numbers of pistons are better in some regards: durability and resistance to heat-based fade and damage.

But for RAW BRAKING POWER ONLY, area is king.

Of course, all of the above assumes that the caliper is stiff enough to actually apply the force to the pads. If you have a caliper with giant pistons but it is too flexible to properly clamp the pads then you will never realize the benefits of all that area. As I noted at the end of my original post, the stiffness of the calipers might affect the results. I have no way to measure the stiffness of the various calipers discussed, so I can't really comment on that. However, it is something to think about.
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Old 12-01-2005, 05:49 PM
Turbobuick Turbobuick is offline
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Default Re: The Final Word on front disc brakes

I'm not sure were you are going with this but in all the disc brake arrangements you have listed above the 13" rotors with PBR calipers are going to be FAR superior to anything else you have listed, and I know this from experience. "Raw braking power" is going to be determined by many factors other than piston size. Pad size, fluid dynamics, rotor size, heat, caliper size, all contribute greatly to the overall design and function. MC bore diameter has nothing to do with this and has to do with pedal travel and feel.

I'm no expert in braking, by far, but I have run the 1LE brakes, wilwoods and the 13" PBR brakes on a race track (road racing and drag racing) and will take a 13" brake with PBR caliper over the others listed, any day of the week and especially on Sunday!
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Old 12-01-2005, 07:51 PM
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Default Re: The Final Word on front disc brakes

Master Cylinder bore has a large effect on braking power.

If you get a smaller bore master cylinder, then you are increasing the pressure generated in the brake lines with the same amount of pedal effort. That is going to improve the caliper grip force by the same amount.

A 10% smaller (area) master cylinder would be an EXACT EQUIVALENT to 10% larger (area) pistons in all your brakes. Of course, there is a practical limit: too small a MC and you won't have enough fluid displaced to properly brake.

Read any basic book on Hydraulics if that explanation isn't clear.

I think that the success of the PBR setup is that the PBR calipers are probably stiffer than OEM (and others too?). Therefore, they are capable of applying a greater force DESPITE the fact that they have a smaller active area than some of the other choices.

Again, I hate to beat a dead horse but I've clearly stated that none of this takes stiffness into account.
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Old 12-02-2005, 10:10 PM
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Default Re: The Final Word on front disc brakes

Hey everyone, I made some edits to my original post.

I visited the local O'Reily today and examined a few different calipers. It turns out that the "B Body" heavy duty caliper (e.g. 12" Caprice brakes) has a 2.75" piston. I THINK that this is the same caliper used on 3/4 ton trucks during the 70's as well....I haven't compared them side by side, but it looks very similar.

This means that a properly done 12" B-body swap is going to have very, very, good performance: nearly a 50% upgrade!

The B body brake parts are very cheap. O'Reily quoted me $15 for a caliper ($5 core) and $26 for an IROC brake disc. The downside, of course, is that you have to drop a few hundred $$$ on control arms in order to use the B-Body parts....and even then you still need spindles.

Wilwood (and perhaps others) make an aftermarket caliper that is a drop-in replacement for the B body style. The piston diameter is the same, but Wilwood claims their caliper is significantly lighter than OEM, and that it is much stiffer as well. Unfortunatley, these are fairly expensive; $125 each from Summit.
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Old 12-06-2005, 06:49 AM
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Default Re: The Final Word on front disc brakes

i see.. thats good stuff but.. my stock brakes work just fine

if your brakes dont work that good, try improving the rears, with bigger cylinders. and ive also heard, from i think it was ken mosher, but dont quote me on that..that you can take the two larger shoes, and put them onto one side, then buy another set, and use those two large shoes on the other side. then throw some aluminum drums on there. im guessing the aluminum drums keep things a tad cooler, as i know aluminum gives up its heat really quickly, and that has to be good news for break shoes. if you run this option, and everything else is tuned to where its supposed to be, you should be just fine. if youre trying to boost at the line, and your brakes cant hold ya, do a line lock or trans brake. but, for as hard as i drive my gn, (which is kinda hard) my brakes work just fine.
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Old 12-06-2005, 11:32 AM
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Default Re: The Final Word on front disc brakes

Actually, I don't endorse the two long shoe rear brakes mod ... my thought has always been that the longer shoe distorts more (much to Doc's point with the front caliper stiffness discussion).

I run the larger rear cylinders and soft compound organic rear shoes (again, to Doc's point about friction coefficient ... the cheapy shoes won't wear as long, but usually have better friction).

So ... anyway, I think the discussion above was launched by the thought of running discs on all four corners, so the rears are probably off point.
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Old 01-20-2006, 07:48 PM
Dave Burchfiel Dave Burchfiel is offline
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Default Re: The Final Word on front disc brakes

Ok! I've been reading about brakes and I'm still not sure what to do. Since 1987 my brakes have been terrible. as far as I'm concerned its the worst thing about the GN. Fairly early (when my accumulator failed on the powermaster) converted to vacuum brakes. I've bled them, replaced the master cylinder and vacuum acumulator twice, replaced the shoes with soft compounds, replaced the pads with semi metalic (that may have even made them worse) and I'm surprised in the 140,000 miles I've driven the car I haven't wrecked it (at least not because of the brakes). The pedal travel is way too long before the brakes engage; yet not spongy. (there is no air in the system) I can't lock the brakes if I stand on the pedal with both feet. Once in a while they might give a hint of a lock up. Sometimes but not often the pedal is just hard as a rock with almost no braking. Combination valve problems?

I'm thinking of going to 13" baer brakes in the front and 12" in the rear but after reading the forum I'm hesitant. Doc states that pad area has no affect on braking and it's strictly force and cf. I remember that from physics yet I think more is going on or why would we run nice fat tires since area (contact patch) wouldn't change the traction.
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