They may be a separate selection in the upgrades menu, but for the most part they seem to have the same stats as race tires, which is the important part in this context.
I think it depends on the car. I also think that they correspond to one of the standard tire tiers, and the tiers below are unavailable (i.e., you can’t downgrade the tires). The Jaguar Project 7 HE is telling here. You can get race tires for it, up the PI, and lose the tire lettering. So my guess is that this car’s HE tires are in the Sport tier.
Its kinda annoying not being able to downgrade tires on he cars. it makes all a class horizon edition cars useless online as the tires are upgraded too much to get enough power to be competitive. Most of my fast a cars are running street tires, helps to get far enough infront of the rammers that they cant bomb you lol