The problem with taxing tires is that most tires are good for 40,000 to 50,000 miles, which may not all be driven in one city, county, or state. How do you pay for using the roads in Los Angeles if you bought the tires in Las Vegas?
-PJ
Why, it's simple... you wind up paying for the roads closest to where you live. Places with the highest population density will have the highest revenue, which is appropriate because they also have the most expensive upkeep for roads.
The free road upkeep you get by driving on roads in other areas is compensated by the free upkeep they get by driving on your roads. Best part is, if you don't want to support your local road maintenance efforts, just minimize your driving. Kind of like it is already with the gas tax.