I remember asking Helo about adding white walls and he said it's not possible to create them since they would be too high-poly. I think lettering on the tyres is the same too.
I didnt say that, i said there is a limit of wheels in GTA SA and the tires replace wheels. One tire design takes 3 wheel slots (3 sizes). We already replace 3 for normal tires, 3 for offroad tires, 1 for A-Type tires and 1 for Locust tires. There simply arent enough to implement more tire design.