Keeping the correct tire pressure will save fuel. But the fantastical claims regarding the amount of saved fuel is just that- fantasy.
I thought so too when I heard it, but in
theory it's not fantasy.
It's estimated that 1.2 to 2.8 billion gallons of gasoline are wasted annually due to tire underinflation. It's estimated that by 2030, offshore oil could produce 1.4 billion gallons of gasoline annually.
But Americans are no more going to keep their tires properly inflated than drive the speed limit, so the issue is moot.