Brake Bias

ResIpsa

Here is a thread I started on G35Driver trying to defend my Wilwood’s on my old G. I think it can be of some use in understanding how brake bias works.

Stop-Tech’s front BBK reduces stopping distance by utilizing a smaller piston area than stock. Yes, the Stop-Tech front caliper has less stopping torque than the stock caliper.

The proper question to ask is the size of the pistons and the rotor. I’ll explain.

First, all brake kits operate on the same principals. Hydraulic fluid is pushed through a line that compresses a piston which pushes the pads on the rotor.

Second, total piston area determines the torque of any given caliper. For example, the stock caliper on a 2005 6MT has two 1.75 inch pistons. Do some math and the total area is 4.8 inches. This calculation uses the pistons on only one side of the caliper. So, a six piston caliper’s piston area would be based on 3 pistons. Strangely, the stock sliding calipers brake as if they had identical opposed pistons (why? Ask a physicist).

Third, the number of pistons does not affect torque. I doesn’t matter if you get 4 inches of piston area with one big piston or 9 tiny pistons.

Fourth, rotor diameter effects brake torque. For example, if the only modification you did to your stock brakes was increase the front rotors to 14 inches then front brake bias would increase 2%. A 13 inch rear rotor would reduce front bias 2%. That rear rotor upgrade is starting to look pretty good now...

Fifth, our cars come from the factory overly front brake biased (74% front/26% rear). Although this increases stopping distance, a front biased vehicle is easier to control.

Therefore, reducing front brake bias will balance the car and decrease stopping times. However, shift the bias too far and the rears may lock up before the front. VERY DANGEROUS!

Stop-Tech has determined that magic amount of brake bias to magically balance a 350z/G35. I would love to know the piston area of the Stop-Tech front BBK.

So you want to know the effectiveness of your specific BBK. Get a ruler and measure the piston areas and rotor diameter.

Then use a brake bias calculator like the one at Tech; Brake Bias. If the ratio is the same as stock, then your brake distance will be unchanged. If the ratio is more front biased you will take longer to stop and unnecessarily burden your front brakes.

If you are going front only, make sure the total piston area (and front brake bias) is slightly less than stock. A general rule of thumb is no more than 5%. Also, search the forums and call the distributor to determine if there are any problems with that specific BBK locking the rears.

For example, I have Wilwood 6 piston calipers on 13 inch rotors. The total piston area is 4.06 or .74 inches less than stock resulting in 72%/28% bias or 2% more rear bias.

A Wilwood 6 piston superlight BBK with a 13 inch rotor will stop in a shorter distance than stock.

Of course different BBK's will have better heat dissipating characteristics, pedal modulation, etc... but that is for another post.

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