Surface Properties are as in the name, properties to be assigned to grounds and floors for making them more realistic by generating particles using Re-Volt's particle generator or adding special behavior on the car (such as bumping,shaking)
Technically, the surface properties are directly assigned to NCP (World mesh's collision file or mesh's collision file).  According to Re-Volt code there are 23 properties.
3D track creators are able to use these properties by assigning specified smooth from Smoothing Group then exporting the meshes to ASE then importing to Re-Volt comprehensible 3D model using ASETools.
Propeties from the code