[Argess]

Well, using all 4 for piston area is OK, but you can only use the piston area of two of them to calculate the force on the pads.

Let's say you weigh 200 lbs. Put a piece of plywood on the floor and stand on it. You are putting a force of 200 lbs on the plywood.

Now put the plywood against a wall and push on it with 200 lbs of force. The plywood is being compressed the same... with 200 lbs of force.

Next stand the plywood up on edge in the middle of the floor. You press on one side with a force of 200 lbs. I press on the other side with 200 lbs. The plywood is compressed the same as if it were against the wall, or the floor.... with only 200 lbs of force.

Hope this makes sense.

Now 4 pistons are better than two as they take up small misalignments between the caliper and rotor, so it's a worthwhile change.