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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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