A rotor supported on rollers will also see some axial forces from misalignments of the rollers. Changes in this axial force, say from changes in unbalance force, are likely to be almost synchronous, but out of phase enough to obscure balance resolution. Air bearings impart zero axial force on the rotor, avoiding this error source. The radial friction is also near zero and so the heavy spot finds the low point of rotation when the air pressure is supplied to the air bearings. This improves the resolution in static balancing by an order of magnitude, because the static breakaway coefficient of friction of air bearings is 10 times lower than that of rolling elements for a typical roller stand, or horizontal-way static balancing set-up.
An additional and very practical benefit of replacing the hard rollers with air bearings is that the rotor can be supported on its bearing journals without fear of damage to the bearing surface from point contact with a hard roller or from contamination between the rolling surfaces at speed. Balance Bearing faces are made from graphite, presenting a relatively soft, large contact area and non-scoring bearing surface should contact occur.