Here's a definitive answer
Ahem. Being an automotive engineer with some credence elsewhere, you can trust me on this one:
There is some confusion in the industry between track width and tread width terminology. SAE refers to it one way, the government the other.
SAE Track width is the distance between the geometric wheel centerlines as measured at the axle height. Some manufacturers (Ford Included) report this in their advertising as the track width.
SAE Tread width is the distance between the tire centerlines at the tire contact patches as measured at the ground. The government refers to this as the track width.
The difference between these measurements is caused by camber angle. If the vehicle has a negative camber angle, the SAE Tread Width is going to be larger than the SAE Track width.
Hopes this helps.