[aerohead]

1) The thickness/ chord ratio for a symmetrical section of minimum drag is 3.92:1.
2) The data is from the drag table for the above-named, appearing on page-244, of AERO-HYDRODYNAMICS OF SAILING, by Marchaj.
3) I published a dedicated graphic for this table in 2012 here at the Forum.
4) Just as with streamline bodies of revolution, there is one ratio at which both surface friction drag and pressure drag are at minimums, at the 'bottom of the drag bucket.'
5) Extending the length increases overall drag due to increased friction drag.
6) Reducing length increases overall drag due to increased pressure drag.
7) Peering upwards, through a 'transparent' road, a wheel fairing package for either front, or rear wheels, one might expect a minimum drag, as a first principle, when the fairing constituted the 3.92:1 ratio.
8) The 'aft-body' portion behind the axle centerline would be 2.378 X the fairings width.