Originally Posted by
CraigMBA
To keep people from grinding all the tread off, and coming up with "magic" one run tires.
The slicks are horrible (and the other tread pattern is worse) on asphalt, BTW. Even if they were legal, you wouldn't want to run them because they're slow.
+1 on all of these opinions. Having a tread pattern rule prevents people from ruining brand new sets of tires (which, IMO, work best when treaded), and the other two vintage tire varieties are absolutely terrible.