You're both right guys
Snapper is right about the ET, positive ET makes the weels go "inside" the car.
But Alga is right to add 2x the ET to the track to calculate the distance between the two wheel mounting faces ad Thaioz asked.
The track is the distance between the 2 centrelines of the wheels as Alga says, and with a positive ET, the centrelines are more "inside" the car than the wheel mounting faces.
So the distance between the two wheel mounting faces, it is definitely the distance between the 2 centrelines of the wheels (track)+ the 2x the ET of the wheels the track has been measured with.
Hope I'm not adding more confusing to this thread
