It shouldn't so much be how big your rubber is. You can crame things under a truck, doesn't mean it won't rub, but as long as its not extruding from the side of the body then its fine, if it is you have to put some sort of flare/mudflap on like the rigs...

As for the DOT part... That just means it been safty tested and is worthy of travel on reg. roads.

Atleast thats what i've been told....