many car tires are strictly unidirectional

i've had road bike tires that are unidirectional as well. however, its my personal opinion that that doesnt mean much.

larger, knobby mtb tires have angled knobs designed to shed mud or to grip in loosely-packed surfaces.... with those i'll adhere to the mounting directions.

with skinny road tires? nah. hell, an ideal tire would be bald and have no specific direction of optimum grip/performance