What sets brake bias
Each brake's torque depends on three things: how much piston area pushes the pads, how far from the hub the pads grip the rotor (effective radius), and how grippy the pad compound is. With the same line pressure at both ends, the ratio of front to rear torque is your hydraulic bias.
Why a big brake kit can make braking worse
Bigger front rotors and calipers add front torque, which moves bias forward. Too far forward and the fronts lock (or ABS kicks in) before the rears do their share, so stopping distance can actually get longer. Good kits are matched to keep bias close to stock; use this to check before you buy.
Pads change bias too
Running a grippier track pad on the front only raises front torque the same way a bigger caliper does. If you change compounds, change both ends or check the numbers.
What this doesn't include
Most road cars have a proportioning valve or electronic brake-force distribution that reduces rear pressure, and weight shifts forward under braking. This tool compares setups on the same car; it doesn't predict the exact bias you'll feel on track.