An easy measure for rolling circumference is to mark each tire at the bottom with a chalk line and a mark on the driveway at the same spot.
This line would be where the the tire's plum center-line meets the pavement...
Now roll the car foward one full tire revolution and mark the pavement again... the distance between the pavement marks should be the same for all 4 tires .. this is the Rolling cicumference of each tire and you can now see were tire pressure can make a difference [ along with different brand tires]