Piston sizing...

[jeffandre]

We have all heard that the front brakes do the most work, and of course weight distribution and how the vehicle weight responds to acceleration has an effect, but in the 'classroom' so to speak I have heard 2 basic formulas and need to know which is right.

In the past I read from somewhere in the old posts that the rear caliper piston area should be no more than 60% of the front caliper piston area. Then I read recently that the number is 40%. Which one is preferred for a 3200#+ 2nd Gen with fat tires and stiff suspension? My calcs are shown below for the various piston configurations I may be looking into when the time comes to buy front calipers to go with 14" rotors (I have 13" Eradispeed II rotors in the rear using C5 front calipers).

The C5 front calipers on the rear of the Camaro are 2-piston, 1.75 diameter each. C5 piston d = 0.875"; (0.875)(0.875)(pi) = 2.41"2; 2.41(2 pistons)(2) = 4.82"2. Since a forum post from a knowledgeable person stated that the total rear piston area should be no more than 40% (4.82/12 = 40%), (4.82/8.04 = 60%, per 12/23 posting?!?!) of the total front piston area I have determined the following:



2-piston - 2.76" d each; (1.38)(1.38)(pi) = 5.98; (5.98)(2) = 11.97"2 total piston area. 4.82/11.97 = 40.3%.
- 2.3" d each; (1.15)(1.15)(pi) = 4.15; (4.15)(2) = 8.30"2 total piston area. 4.82/8.3 = 58.1%.

3-piston - 2.25" d each; (1.125)(1.125)(pi) = 3.98; (3.98)(3) = 11.93"2 total piston area. 4.82/11.93 = 40.4%.
- 1.85" d each; (0.925)(0.925)(pi) = 2.69; (2.69)(3) = 8.06"2 total piston area. 4.82/8.06 = 59.8%.

4-piston - 1.95" d each; (0.975)(0.975)(pi) = 2.99; (2.99)(4) = 11.95"2 total piston area. 4.82/11.95 = 40.3%.
- 1.6" d each; (0.8)(0.8)(pi) = 2.01; (2.01)(4) = 8.04"2 total piston area. 4.82/8.3 = 60%.

5-piston - 1.75" d each; (0.875)(0.875)(pi) = 2.41; (2.41)(5) = 12.03"2 total piston area. 4.82/12.03 = 40.1%.
- 1.44" d each; (0.72)(0.72)(pi) = 1.63; (1.63)(5) = 8.14"2 total piston area. 4.82/8.3 = 59.2%.

6-piston - 1.6" d each; (0.8)(0.8)(pi) = 2.01; (2.01)(6) = 12.06"2 total piston area. 4.82/12.06 = 40%.
- 1.32" d each; (0.66)(0.66)(pi) = 1.37; (1.37)(6) = 8.21"2 total piston area. 4.82/8.3 = 59.2%.

8-piston - 1.38" d each; (0.69)(0.69)(pi) = 1.50; (1.50)(8) = 11.97"2 total piston area. 4.82/11.97 = 40.3%.
- 1.14" d each; (0.57)(0.57)(pi) = 1.02; (1.02)(8) = 8.17"2 total piston area. 4.82/8.3 = 59%.

In the end I may have to find a happy medium between 40-60% based on my front to rear weight bias and driving style. Once I guesstimate this, I will then have to get the right master cylinder (possibly a tandem with a balancing bar for fine-tuning), and then finish the package off with the best front pads that get the job done!