Today's physics lesson... Basic Hydraulics...
PSI = Pounds per Square Inch, or Pounds/Sq. In.
I'll use a 1 inch bore and a 3/4 inch bore as examples. So first we have to find the square inch surface area of the piston using the pie are square (π × r2 ) formula.
1" bore = 0.5" radius. 0.5 X 0.5 = 0.25 X 3.14 = 0.785 square inches of surface area.
3/4" bore = 0.375" radius. 0.375 X 0.375 = 0.14 X 3.14 = 0.44 square inches of surface area.
If I were to exert 50 pounds of force on the master cylinder piston with my foot how much pressure will be generated?
50 lbs. / 0.785 sq. in. = 63.7 PSI with the 1 inch bore. (metric conversion; 22.7 kilos = 4.4 Bar)
50 lbs. / 0.44 sq. in. = 113.6 PSI with the 3/4 inch bore. (metric conversion; 22.7 kilos = 7.8 Bar)
So, as you can see, the smaller bore will create more braking pressure with the same pedal force. Or, you could say it will take less leg force to generate the same braking force. However, as alluded to, the smaller bore will move less fluid so it will take a longer pedal stroke to apply the brakes. So it comes down to will a smaller bore master cylinder displace enough brake fluid before bottoming out to apply your brakes safely, yet apply more pressure at the same leg effort? Or do you need a larger bore to get the fluid displacement required, and need a little more leg effort to achieve the braking force needed.