Good question Dan. Despite their name ("Specialty Equipment..."), and the fact they mainly focus on the aftermarket segment, they do include the entire automotive industry (stock, custom, you name it) in general. That also means things like big rigs, industrial vehicles, etc. So depending on the topic or specific situation it can vary, but for the annual report it includes everything (even dealerships, manufacturers, etc), both from domestic and foreign sources - but only for sales in the USA. So your tires would definitely be included regardless of the brand, size, country of origin, application, where purchased, etc, etc. In other words it pretty much included the whole market.
On a somewhat related note, I also saw another report (not automotive specific) about 'earning and spending' in the USA. Seems that 80% of all purchases (in general, across the board) are made by women. Although most large ticket items (houses, cars, etc) are made by men, but so much more of smaller purchases are made by women that it greatly offsets things. That surprised me at first, until I thought back at most of my relationships. The same report also said that much less than half of the household income is generated by women, although they make up nearly half of the workforce. However more than half of all assets are owned by women. Sounds contradictory, I guess it's saying males make the money and give it to women? Going back to the first study, although the automotive industry is finally gaining a much larger proportion of women involved (thankfully), it is still a male dominant industry. So given that women control most of the assets and make almost all of the purchases, it would seem that marketing car stuff to women would be profitable.