Perhaps a word about how Discount Tire works is in order.
Because Discount Tire carries sooooo many brands, they can't possibly store every size, in every brand, in every line of tires. So they leave it up to the individual store to select what each store stocks. In theory, each store has immediately available what is selling.
They also has warehouses - and the same logic is applied. So each warehouse has immediately available what is selling at the stores it services.
So what is stocked at an individual store - or at the regional warehouse - may or may not be a reflection of anything other than what is selling. I would think tires for trailers would be very far down the list of quantity sold.